Table of Contents - WordPress.com · 2018. 3. 2. · Build Web Application with Golang Purpose Because I'm interested in web application development, I used my free time to write

TableofContentsIntroduction

GoEnvironmentConfiguration

Installation

$GOPATHandworkspace

Gocommands

Godevelopmenttools

Summary

Gobasicknowledge

HelloGo

Gofoundation

Controlstatementsandfunctions

struct

Object-oriented

interface

Concurrency

Summary

Webfoundation

Webworkingprinciples

Buildasimplewebserver

HowGoworkswithweb

Getintohttppackage

Summary

HTTPForm

Processforminputs

Validationofinputs

Crosssitescripting

Duplicatesubmissions

Fileupload

Summary

Database

databasesqlinterface

HowtouseMySQL

HowtouseSQLite

HowtousePostgreSQL

HowtousebeedbORM

Summary

Datastorageandsession

Sessionandcookies

HowtousesessioninGo

Sessionstorage

Preventhijackofsession

Summary

Textfiles

Regexp

Templates

Strings

Summary

Webservices

Sockets

WebSocket

Summary

Securityandencryption

CSRFattacks

Filterinputs

XSSattacks

SQLinjection

Passwordstorage

Encryptanddecryptdata

Summary

Internationalizationandlocalization

Timezone

Localizedresources

Internationalsites

Summary

Errorhandlingdebuggingandtesting

Errorhandling

DebuggingbyusingGDB

Writetestcases

Summary

Deploymentandmaintenance

Errorsandcrashes

Deployment

Backupandrecovery

Summary

Buildawebframework

Projectprogram

Customizedrouters

Designcontrollers

Logsandconfigurations

Adddeleteandupdateblogs

Summary

Developwebframework

Staticfiles

Session

Uservalidation

Multi-languagesupport

Summary

References

preface

BuildWebApplicationwithGolangPurpose

BecauseIminterestedinwebapplicationdevelopmentIusedmyfreetimetowritethisbookasanopensourceversionItdoesntmeanthatIhaveaverygoodabilitytobuildwebapplicationsIwouldliketosharewhatIvedonewithGoinbuildingwebapplications

ForthoseofyouwhoareworkingwithPHPPythonRubyyouwilllearnhowtobuildawebapplicationwithGoForthoseofyouwhoareworkingwithCC++youwillknowhowthewebworks

IbelievethepurposeofstudyingissharingwithothersThehappiestthinginmylifeissharingeverythingIveknownwithmorepeople

Donate

AliPay

alipay

EnglishDonatedonate

CommunityQQ群386056972

BBShttpgocnio

Acknowledgments四月份平民AprilCitizen(reviewcode)洪瑞琦HongRuiqi(reviewcode)边疆BianJiang(writetheconfigurationsaboutVimandEmacsforGodevelopment)欧林猫OlingCat(reviewcode)吴文磊WenleiWu(providesomepictures)北极星Polaris(reviewwholebook)雨痕RainTrail(reviewchapter2and3)

LicenseThisbookislicensedundertheCCBY-SA30LicensethecodeislicensedunderaBSD3-ClauseLicenseunlessotherwisespecified

GetStarted

Introduction

1GoEnvironmentConfigurationWelcometotheworldofGoletsstartexploring

Goisafast-compiledgarbage-collectedconcurrentsystemsprogramminglanguageIthasthefollowingadvantages

CompilesalargeprojectwithinafewsecondsProvidesasoftwaredevelopmentmodelthatiseasytoreasonaboutavoidingmostoftheproblemsassociatedwithC-styleheaderfilesIsastaticlanguagethatdoesnothavelevelsinitstypesystemsousersdonotneedtospendmuchtimedealingwithrelationsbetweentypesItismorelikealightweightobject-orientedlanguagePerformsgarbagecollectionItprovidesbasicsupportforconcurrencyandcommunicationDesignedformulti-corecomputers

GoisacompiledlanguageItcombinesthedevelopmentefficiencyofinterpretedordynamiclanguageswiththesecurityofstaticlanguagesItisgoingtobethelanguageofchoiceformodernmulti-corecomputerswithnetworkingForthesepurposestherearesomeproblemsthatneedtoinherentlyberesolvedatthelevelofthelanguageofchoicesuchasarichlyexpressivelightweighttypesystemanativeconcurrencymodelandstrictlyregulatedgarbagecollectionForquitesometimenopackagesortoolshaveemergedthathaveaimedtosolvealloftheseproblemsinapragmaticfashionthuswasbornthemotivationfortheGolanguage

InthischapterIwillshowyouhowtoinstallandconfigureyourownGodevelopmentenvironment

LinksDirectoryNextsectionInstallation

11Installation

ThreewaystoinstallGoTherearemanywaystoconfiguretheGodevelopmentenvironmentonyourcomputerandyoucanchoosewhicheveroneyoulikeThethreemostcommonwaysareasfollows

OfficialinstallationpackagesTheGoteamprovidesconvenientinstallationpackagesinWindowsLinuxMacandotheroperatingsystemsThisisprobablytheeasiestwaytogetstartedYoucangettheinstallersfromtheGolangDownloadPage

InstallityourselffromsourcecodePopularwithdeveloperswhoarefamiliarwithUnix-likesystems

Usingthird-partytoolsTherearemanythird-partytoolsandpackagemanagersforinstallingGolikeapt-getinUbuntuandhomebrewforMac

IncaseyouwanttoinstallmorethanoneversionofGoonacomputeryoushouldtakealookatatoolcalledGVMItisthebesttoolIveseensofarforaccomplishingthistaskotherwiseyoudhavetodealwithityourself

InstallfromsourcecodeTocompileGo15andupwardsyouonlyneedthepreviousversionofGoasGohasachievedbootstrappingYouonlyneedGotocompileGo

TocompileGo14downwardsyouwillneedaCcompilerassomepartsofGoarestillwritteninPlan9CandATampTassembler

OnaMacifyouhaveinstalledXcodeyoualreadyhavethecompiler

OnUnix-likesystemsyouneedtoinstallgccorasimilarcompilerForexampleusingthepackagemanagerapt-get(includedwithUbuntu)onecaninstalltherequiredcompilersasfollows

sudoapt-getinstallgcclibc6-dev

OnWindowsyouneedtoinstallMinGWinordertoinstallgccDontforgettoconfigureyourenvironmentvariablesaftertheinstallationhascompleted(EverythingthatlookslikethismeansitscommentedbyatranslatorIfyouareusing64-bitWindowsyoushouldinstallthe64-bitversionofMinGW)

AtthispointexecutethefollowingcommandstoclonetheGosourcecodeandcompileit(ItwillclonethesourcecodetoyourcurrentdirectorySwitchyourworkpathbeforeyoucontinueThismaytakesometime)

gitclonehttpsgogooglesourcecomgo

cdgosrc

allbash

AsuccessfulinstallationwillendwiththemessageALLTESTSPASSED

OnWindowsyoucanachievethesamebyrunningallbat

IfyouareusingWindowstheinstallationpackagewillsetyourenvironmentvariablesautomaticallyInUnix-likesystemsyouneedtosetthesevariablesmanuallyasfollows(IfyourGoversionisgreaterthan10youdonthavetoset$GOBINanditwillautomaticallyberelatedtoyour$GOROOTbinwhichwewilltalkaboutinthenextsection)

Installation

exportGOROOT=$HOMEgo

exportGOBIN=$GOROOTbin

exportPATH=$PATH$GOROOTbin

Ifyouseethefollowinginformationonyourscreenyoureallset

Figure11Informationafterinstallingfromsourcecode

OnceyouseetheusageinformationofGoitmeansyouhavesuccessfullyinstalledGoonyourcomputerIfitsaysnosuchcommandcheckthatyour$PATHenvironmentvariablecontainstheinstallationpathofGo

UsingthestandardinstallationpackagesGohasone-clickinstallationpackagesforeverysupportedoperatingsystemThesepackageswillinstallGoinusrlocalgo(cGoinWindows)bydefaultOfcoursethiscanbemodifiedbutyoualsoneedtochangealltheenvironmentvariablesmanuallyasIveshownabove

Howtocheckifyouroperatingsystemis32-bitor64-bit

Ournextstepdependsonyouroperatingsystemtypesowehavetocheckitbeforewedownloadthestandardinstallationpackages

IfyouareusingWindowspressWin+RandthenrunthecommandtoolTypethesysteminfocommandanditwillshowyousomeusefulsysteminformationFindthelinethatsayssystemtype-ifyouseex64-basedPCthatmeansyouroperatingsystemis64-bit32-bitotherwise

Istronglyrecommenddownloadingthe64-bitpackageifyouareaMacuserasGonolongersupportspure32-bitprocessorsonMacOSX

Linuxuserscantypeuname-aintheterminaltoseesysteminformationA64-bitoperatingsystemwillshowthefollowing

ltsomedescriptiongtx86_64x86_64x86_64GNULinux

somemachinessuchasUbuntu1004willshowasfollowing

x86_64GNULinux

32-bitoperatingsystemsinsteadshow

ltsomedescriptiongti686i686i386GNULinux

Gotothedownloadpagechoosego142darwin-386pkg(Thelaterversionhasno32-bitdownload)for32-bitsystemsandgo183darwin-amd64pkgfor64-bitsystemsGoingallthewaytotheendbyclickingnext~gobinwillbeaddedtoyoursystems$PATHafteryoufinishtheinstallationNowopentheterminalandtypegoYoushouldseethesameoutputshowninfigure11

Gotothedownloadpagechoosego183linux-386targzfor32-bitsystemsandgo183linux-amd64targzfor64-bitsystemsSupposeyouwanttoinstallGointhe$GO_INSTALL_DIRpathUncompressthetargztoyourchosenpathusingthecommandtarzxvfgo183linux-amd64targz-C$GO_INSTALL_DIRThensetyour$PATHwiththefollowingexportPATH=$PATH$GO_INSTALL_DIRgobinNowjustopentheterminalandtypegoYoushouldnowseethesameoutputdisplayedinfigure11

Installation

Windows

Gotothedownloadpagechoosego183windows-386msifor32-bitsystemsandgo183windows-amd64msifor64-bitsystemsGoingallthewaytotheendbyclickingnextcgobinwillbeaddedtopathNowjustopenacommandlinewindowandtypegoYoushouldnowseethesameoutputdisplayedinfigure11

Usethird-partytools

GVMisaGomulti-versioncontroltooldevelopedbyathird-partylikervmforrubyItsquiteeasytouseInstallgvmbytypingthefollowingcommandsinyourterminal

bashltlt(curl-s-S-Lhttpsrawgithubcommoovwebgvmmasterbinscriptsgvm-installer)

ThenweinstallGousingthefollowingcommands

gvminstallgo183

gvmusego183

Aftertheprocesshasfinishedyoureallset

apt-get

UbuntuisthemostpopulardesktopreleaseversionofLinuxItusesapt-gettomanagepackagesWecaninstallGousingthefollowingcommands

sudoadd-apt-repositoryppagophersgo

sudoapt-getupdate

sudoapt-getinstallgolang-go

wgethttpsstoragegoogleapiscomgolanggo183linux-amd64targz

sudotar-xzfgo183linux-amd64targz-Cusrlocal

Goenvironment

exportGOROOT=usrlocalgo

exportPATH=$PATH$GOBIN

exportGOPATH=$HOMEgopath

Startingfromgo18TheGOPATHenvironmentvariablenowhasadefaultvalueifitisunsetItdefaultsto$HOMEgoonUnixandUSERPROFILEgoonWindows

HomebrewHomebrewisasoftwaremanagementtoolcommonlyusedinMactomanagepackagesJusttypethefollowingcommandstoinstallGo

1 InstallHomebrew

usrbinruby-e$(curl-fsSLhttpsrawgithubusercontentcomHomebrewinstallmasterinstall)

Installation

1 InstallGo

brewupdateampampbrewupgrade

brewinstallgo

LinksDirectoryPrevioussectionGoenvironmentconfigurationNextsection$GOPATHandworkspace

Installation

12$GOPATHandworkspace

$GOPATHGotakesauniqueapproachtomanagethecodefileswiththeintroductionofa$GOPATHdirectorywhichcontainsallthegocodeinthemachineNotethatthisisdifferentfromthe$GOROOTenvironmentvariablewhichstateswheregoisinstalledonthemachineWehavetodefinethe$GOPATHvariablebeforeusingthelanguageinnixsystemsthereisafilecalledprofileweneedtoappendthebelowexportstatementtothefileTheconceptbehindgopathisanovelonewherewecanlinktoanygocodeatanyinstantoftimewithoutambiguity

Startingfromgo18theGOPATHenvironmentvariablenowhasadefaultvalueifitisunsetItdefaultsto$HOMEgoonUnixandUSERPROFILEgoonWindows

InUnix-likesystemsthevariableshouldbeusedlikethis

exportGOPATH=$HOMEmygo

InWindowsyouneedtocreateanewenvironmentvariablecalledGOPATHthensetitsvaluetocmygo(Thisvaluedependsonwhereyourworkspaceislocated)

ItsOKtohavemorethanonepath(workspace)in$GOPATHbutrememberthatyouhavetouse(inWindows)tobreakthemupAtthispointgogetwillsavethecontenttoyourfirstpathin$GOPATHItishighlyrecommendedtonothavemultiplesversionstheworstcaseistocreateafolderbythenameofyourprojectrightinside$GOPATHitbreakseverythingthatthecreatorswerewishingtochangeinprogrammingwiththecreationofgolanguagebecausewhenyoucreateafolderinside$GOPATHyouwillreferenceyourpackagesasdirectlyasandthisbreaksalltheapplicationswhichwillimportyourpackagebecausethegogetwontfindyourpackagePleasefollowconventionsthereisareasonconventionsarecreated

In$GOPATHyoumusthavethreefoldersasfollows

srcforsourcefileswhosesuffixisgocgspkgforcompiledfileswhosesuffixisabinforexecutablefiles

InthisbookIusemygoasmyonlypathin$GOPATH

PackagedirectoryCreatepackagesourcefilesandfolderslike$GOPATHsrcmymathsqrtgo(mymathisthepackagename)(Authorusesmymathashispackagenameandthesamenameforthefolderthatcontainsthepackagesourcefiles)

EverytimeyoucreateapackageyoushouldcreateanewfolderinthesrcdirectorywiththenotableexceptionofmainforwhichmainfoldercreationisoptionalFoldernamesareusuallythesameasthepackagethatyouaregoingtouseYoucanhavemulti-leveldirectoriesifyouwanttoForexampleifyoucreatethedirectory$GOPATHsrcgithubcomastaxiebeedbthenthepackagepathwouldbegithubcomastaxiebeedbThepackagenamewillbethelastdirectoryinyourpathwhichisbeedbinthiscase

Executefollowingcommands(Nowauthorgoesbacktotalkexamples)

cd$GOPATHsrc

mkdirmymath

Createanewfilecalledsqrtgotypethefollowingcontenttoyourfile

$GOPATHandworkspace

Sourcecodeof$GOPATHsrcmymathsqrtgo

packagemymath

funcSqrt(xfloat64)float64

fori=0ilt1000i++

z-=(zz-x)(2x)

returnz

NowmypackagedirectoryhasbeencreatedanditscodehasbeenwrittenIrecommendthatyouusethesamenameforyourpackagesastheircorrespondingdirectoriesandthatthedirectoriescontainallofthepackagesourcefiles

CompilepackagesWevealreadycreatedourpackageabovebuthowdowecompileitforpracticalpurposesTherearetwowaystodothis

1 Switchyourworkpathtothedirectoryofyourpackagethenexecutethegoinstallcommand2 Executetheabovecommandexceptwithafilenamelikegoinstallmymath

Aftercompilingwecanopenthefollowingfolder

cd$GOPATHpkg$GOOS_$GOARCH

youcanseethefilewasgenerated

mymatha

ThefilewhosesuffixisaisthebinaryfileofourpackageHowdoweuseit

Obviouslyweneedtocreateanewapplicationtouseit

Createanewapplicationpackagecalledmathapp

cd$GOPATHsrc

mkdirmathapp

cdmathapp

vimmaingo

Writethefollowingcontenttomaingo

$GOPATHsrcmathappmaingosourcecode

packagemain

import(

mymath

funcmain()

fmtPrintf(HelloworldSqrt(2)=vnmymathSqrt(2))

Tocompilethisapplicationyouneedtoswitchtotheapplicationdirectorywhichinthiscaseis$GOPATHsrcmathappthenexecutethegoinstallcommandNowyoushouldseeanexecutablefilecalledmathappwasgeneratedinthedirectory$GOPATHbinTorunthisprogramusethemathappcommandYoushouldseethefollowingcontentinyourterminal

HelloworldSqrt(2)=1414213562373095

$GOPATHandworkspace

InstallremotepackagesGohasatoolforinstallingremotepackageswhichisacommandcalledgogetItsupportsmostopensourcecommunitiesincludingGithubGoogleCodeBitBucketandLaunchpad

gogetgithubcomastaxiebeedb

Youcanusegoget-uhelliptoupdateyourremotepackagesanditwillautomaticallyinstallallthedependentpackagesaswell

ThistoolwillusedifferentversioncontroltoolsfordifferentopensourceplatformsForexamplegitforGithubandhgforGoogleCodeThereforeyouhavetoinstalltheseversioncontroltoolsbeforeyouusegoget

Afterexecutingtheabovecommandsthedirectorystructureshouldlooklikefollowing

$GOPATH

|-githubcom

|-astaxie

|-beedb

|--$GOOS_$GOARCH

|-githubcom

|-astaxie

|-beedba

Actuallygogetclonessourcecodetothe$GOPATHsrcofthelocalfilesystemthenexecutesgoinstall

Youcanuseremotepackagesinthesamewaythatweuselocalpackages

importgithubcomastaxiebeedb

DirectorycompletestructureIfyouvefollowedalloftheabovestepsyourdirectorystructureshouldnowlooklikethefollowing

mathapp

$GOOS_$GOARCHsuchasdarwin_amd64linux_amd64

mymatha

githubcom

astaxie

beedba

mathapp

maingo

mymath

sqrtgo

githubcom

astaxie

beedbgo

utilgo

Nowyouareabletoseethedirectorystructureclearlybincontainsexecutablefilespkgcontainscompiledfilesandsrccontainspackagesourcefiles

(TheformatofenvironmentvariablesinWindowsisGOPATHhoweverthisbookmainlyfollowstheUnix-stylesoWindowsusersneedtoreplacetheseyourself)

$GOPATHandworkspace

LinksDirectoryPrevioussectionInstallationNextsectionGocommands

$GOPATHandworkspace

13Gocommands

GocommandsTheGolanguagecomeswithacompletesetofcommandoperationtoolsYoucanexecutethegocommandontheterminaltoseethem

Figure13Gocommanddisplaysdetailedinformation

TheseareallusefulforusLetsseehowtousesomeofthem

gobuildThiscommandisforcompilingtestsItwillcompilepackagesanddependenciesifitsnecessary

Ifthepackageisnotthemainpackagesuchasmymathinsection12nothingwillbegeneratedafteryouexecutegobuildIfyouneedthepackagefileain$GOPATHpkgusegoinstallinsteadIfthepackageisthemainpackageitwillgenerateanexecutablefileinthesamefolderIfyouwantthefiletobegeneratedin$GOPATHbinusegoinstallorgobuild-o$PATH_HEREaexeIftherearemanyfilesinthefolderbutyoujustwanttocompileoneofthemyoushouldappendthefilenameaftergobuildForexamplegobuildagogobuildwillcompileallthefilesinthefolderYoucanalsoassignthenameofthefilethatwillbegeneratedForinstanceinthemathappproject(insection12)usinggobuild-oastaxieexewillgenerateastaxieexeinsteadofmathappexeThedefaultnameisyourfoldername(non-mainpackage)orthefirstsourcefilename(mainpackage)

(AccordingtoTheGoProgrammingLanguageSpecificationpackagenamesshouldbethenameafterthewordpackageinthefirstlineofyoursourcefilesItdoesnthavetobethesameasthefoldernameandtheexecutablefilenamewillbeyourfoldernamebydefault)

gobuildignoresfileswhosenamesstartwith_orIfyouwanttohavedifferentsourcefilesforeveryoperatingsystemyoucannamefileswiththesystemnameasasuffixSupposetherearesomesourcefilesforloadingarraysTheycouldbenamedasfollows

array_linuxgo|array_darwingo|array_windowsgo|array_freebsdgo

gobuildchoosestheonethatsassociatedwithyouroperatingsystemForexampleitonlycompilesarray_linuxgoinLinuxsystemsandignoresalltheothers

gocleanThiscommandisforcleaningfilesthataregeneratedbycompilersincludingthefollowingfiles

_objolddirectoryofobjectleftbyMakefiles

_testolddirectoryoftestleftbyMakefiles

_testmaingoolddirectoryofgotestleftbyMakefiles

testoutolddirectoryoftestleftbyMakefiles

buildoutolddirectoryoftestleftbyMakefiles

[568ao]objectfilesleftbyMakefiles

DIR(exe)generatedbygobuild

DIRtest(exe)generatedbygotest-c

MAINFILE(exe)generatedbygobuildMAINFILEgo

Gocommands

IusuallyusethiscommandtocleanupmyfilesbeforeIuploadmyprojecttoGithubTheseareusefulforlocaltestsbutuselessforversioncontrol

gofmtandgofmtThepeoplewhoareworkingwithCC++shouldknowthatpeoplearealwaysarguingaboutwhichcodestyleisbetterKampR-styleorANSI-styleHoweverinGothereisonlyonecodestylewhichisenforcedForexampleleftbracesmustonlybeinsertedattheendoflinesandtheycannotbeontheirownlinesotherwiseyouwillgetcompileerrorsFortunatelyyoudonthavetoremembertheserulesgofmtdoesthisjobforyouJustexecutethecommandgofmtltFilenamegtgointerminalIdontusethiscommandverymuchbecauseIDEsusuallyexecutethiscommandautomaticallywhenyousavesourcefilesIwilltalkmoreaboutIDEsinthenextsection

gofmtisjustanaliaswhichrunsthecommandgofmt-l-wonthepackagesnamedbytheimportpaths

Weusuallyusegofmt-winsteadofgofmtThelatterwillnotrewriteyoursourcefilesafterformattingcodegofmt-wsrcformatsthewholeproject

gogetThiscommandisforgettingremotepackagesSofaritsupportsBitBucketGithubGoogleCodeandLaunchpadThereareactuallytwothingsthathappenafterweexecutethiscommandThefirstthingisthatGodownloadsthesourcecodethenexecutesgoinstallBeforeyouusethiscommandmakesureyouhaveinstalledalloftherelatedtools

BitBucket(MercurialGit)

Github(git)

GoogleCode(GitMercurialSubversion)

Launchpad(Bazaar)

InordertousethiscommandyouhavetoinstallthesetoolscorrectlyDontforgettoupdatethe$PATHvariableBythewayitalsosupportscustomizeddomainnamesUsegohelpimportpathformoredetailsaboutthis

goinstallThiscommandcompilesallpackagesandgeneratesfilesthenmovesthemto$GOPATHpkgor$GOPATHbin

gotestThiscommandloadsallfileswhosenameinclude_testgoandgeneratestestfilesthenprintsinformationthatlookslikethefollowing

okarchivetar0011s

FAILarchivezip0022s

okcompressgzip0033s

IttestsallyourtestfilesbydefaultUsecommandgohelptestflagformoredetails

godocManypeoplesaythatwedontneedanythird-partydocumentationforprogramminginGo(actuallyIvemadeaCHMalready)Gohasapowerfultooltomanagedocumentationnatively

Gocommands

SohowdowelookuppackageinformationindocumentationForinstanceifyouwanttogetmoredetailsaboutthebuiltinpackageusethegodocbuiltincommandSimilarlyusethegodocnethttpcommandtolookupthehttppackagedocumentationIfyouwanttoseemoredetailsaboutspecificfunctionsusethegodocfmtPrintfandgodoc-srcfmtPrintfcommandstoviewthesourcecode

Executethegodoc-http=8080commandthenopen1270018080inyourbrowserYoushouldseealocalizedgolangorgItcannotonlyshowthestandardpackagesinformationbutalsopackagesinyour$GOPATHpkgItsgreatforpeoplewhoaresufferingfromtheGreatFirewallofChina

OthercommandsGoprovidesmorecommandsthanthosewevejusttalkedabout

gofixupgradecodefromanoldversionbeforego1toanewversionaftergo1

goversiongetinformationaboutyourversionofGo

goenvviewenvironmentvariablesaboutGo

golistlistallinstalledpackages

goruncompiletemporaryfilesandruntheapplication

TherearealsomoredetailsaboutthecommandsthatIvetalkedaboutYoucanusegohelpltcommandgttolookthemup

LinksDirectoryPrevioussection$GOPATHandworkspaceNextsectionGodevelopmenttools

Gocommands

GodevelopmenttoolsInthissectionImgoingtoshowyouafewIDEsthatcanhelpyoubecomeamoreefficientprogrammerwithcapabilitiessuchasintelligentcodecompletionandauto-formattingTheyareallcross-platformsothestepsIwillbeshowingyoushouldnotbeverydifferentevenifyouarenotusingthesameoperatingsystem

LiteIDELiteIDEisanopensourcelightweightIDEfordevelopingGoprojectsonlydevelopedbyvisualfc

Figure14MainpanelofLiteIDE

LiteIDEfeatures

Cross-platformWindowsLinuxMacOS

Cross-compileManagemultiplecompileenvironmentsSupportscross-compilationofGo

ProjectmanagementstandardDocumentationviewbasedon$GOPATHCompilationsystembasedon$GOPATHAPIdocumentationindexbasedon$GOPATH

GosourcecodeeditorCodeoutliningFullsupportofgocodeGodocumentationviewandAPIindexViewcodeexpressionusingF1FunctiondeclarationjumpusingF2GdbsupportAuto-formatwithgofmt

OthersMulti-languagePluginsystemTexteditorthemesSyntaxsupportbasedonKateintelligentcompletionbasedonfull-textCustomizedshortcutsMarkdownsupport

Real-timepreviewCustomizedCSSExportHTMLandPDFConvertandmergetoHTMLandPDF

LiteIDEinstallationInstallLiteIDE

Downloadpage

Godevelopmenttools

Sourcecode

YouneedtoinstallGofirstthendownloadtheversionappropriateforyouroperatingsystemDecompressthepackagetodirectlyuseit

Installgocode

Youhavetoinstallgocodeinordertouseintelligentcompletion

goget-ugithubcomnsfgocode

Compilationenvironment

SwitchconfigurationinLiteIDEtosuityouroperatingsystemInWindowsandusingthe64-bitversionofGoyoushouldchoosewin64astheconfigurationenvironmentinthetoolbarThenchooseOptionsfindLiteEnvintheleftlistandopenfilewin64envintherightlist

GOROOT=cgo

GOBIN=

GOARCH=amd64

GOOS=windows

CGO_ENABLED=1

PATH=GOBINGOROOTbinPATH

ReplaceGOROOT=cgotoyourGoinstallationpathsaveitIfyouhaveMinGW64addcMinGW64bintoyourpathenvironmentvariableforcgosupport

InLinuxandusingthe64-bitversionofGoyoushouldchooselinux64astheconfigurationenvironmentinthetoolbarThenchooseOptionsfindLiteEnvintheleftlistandopenthelinux64envfileintherightlist

GOROOT=$HOMEgo

GOBIN=

GOARCH=amd64

GOOS=linux

CGO_ENABLED=1

PATH=$GOBIN$GOROOTbin$PATH

ReplaceGOROOT=$HOMEgotoyourGoinstallationpathsaveit

$GOPATH$GOPATHisthepaththatcontainsalistofprojectsOpenthecommandtool(orpressCtrl+`inLiteIDE)thentypegohelpgopathformoredetailsItsveryeasytoviewandchange$GOPATHinLiteIDEFollowView-SetupGOPATHtoviewandchangethesevalues

SublimeTextHereImgoingtointroduceyoutheSublimeText3(Sublimeforshort)+GoSublime+gocodeLetmeexplainwhy

Intelligentcompletion

Figure15Sublimeintelligentcompletion

Auto-formatsourcefilesProjectmanagement

Godevelopmenttools

Figure16Sublimeprojectmanagement

Syntaxhighlight

FreetrialforeverwithnofunctionallimitationsYoumaybepromptedonceinawhiletoremindyoutopurchasealicensebutyoucansimplyignoreitifyouwishOfcourseifyoudofindthatitenhancesyourproductivityandyoureallyenjoyusingitpleasepurchaseacopyofitandsupportitscontinueddevelopment

FirstdownloadtheversionofSublimesuitableforyouroperatingsystem

1 PressCtrl+`openthecommandtoolandinputthefollowingcommands

ApplicabletoSublimeText3

importurllibrequestospf=PackageControlsublime-packageipp=sublimeinstalled_packages_path()urllibrequesti

nstall_opener(urllibrequestbuild_opener(urllibrequestProxyHandler()))open(ospathjoin(ipppf)wb)write(urlli

brequesturlopen(httpsublimewbondnet+pfreplace(20))read())

importurllib2ospf=PackageControlsublime-packageipp=sublimeinstalled_packages_path()osmakedirs(ipp)ifnotos

pathexists(ipp)elseNoneurllib2install_opener(urllib2build_opener(urllib2ProxyHandler()))open(ospathjoin(ipp

pf)wb)write(urllib2urlopen(httpsublimewbondnet+pfreplace(20))read())print(PleaserestartSubl

imeTexttofinishinstallation)

RestartSublimeTextwhentheinstallationhasfinishedYoushouldthenfinda`PackageControl`optioninthePref

erencesmenu

[](images14sublime3pngraw=true)

Figure17SublimePackageControl

1 ToinstallGoSublimeSidebarEnhancementsandGoBuildpressCtrl+Shift+ptoopenPackageControlthentypepcip(shortforPackageControlInstallPackage)

Figure18SublimeInstallPackages

NowtypeinGoSublimepressOKtoinstallthepackageandrepeatthesamestepsforinstallingSidebarEnhancementsandGoBuildOnceagainrestarttheeditorwhenitcompletestheinstallation

2 ToverifythattheinstallationissuccessfulopenSublimethenopenthemaingofiletoseeifithasthepropersyntaxhighlightingTypeimporttoseeifcodecompletionpromptsappearAftertypingimportfmttypefmtanywhereaftertheimportdeclarationtoseewhetherornotintelligentcodecompletionforfunctionswassuccessfullyenabled

Ifeverythingisfineyoureallset

Ifnotcheckyour$PATHagainOpenaterminaltypegocodeIfitdoesnotrunyour$PATHwasnotconfiguredcorrectly

VimVimisapopulartexteditorforprogrammerswhichevolvedfromitsslimmerpredecessorViIthasfunctionsforintelligentcompletioncompilationandjumpingtoerrors

vim-goisvimaboveanopen-sourcegolanguageusingthemostextensivedevelopmentenvironmentplug-ins

Thepluginaddressgithubcomfatihvim-go

Godevelopmenttools

VimpluginmanagementarethemainstreamPathogenandVundleButtheaspectsthereofaredifferentPathogenistosolveeachplug-inaftertheinstallationoffilesscatteredtomultipledirectoriesandpoormanagementoftheexistenceVundleistosolvetheautomaticsearchanddownloadplug-insexistThesetwoplug-inscanbeusedsimultaneously

1InstallVundle

mkdir~vimbundle

gitclonehttpsgithubcomgmarikVundlevimgit~vimbundleVundlevim

EditvimrcVundletherelevantconfigurationwillbeplacedinthebeginning(RefertotheVundledocumentationfordetails)

setnocompatiblebeiMprovedrequired

filetypeoffrequired

settheruntimepathtoincludeVundleandinitialize

setrtp+=~vimbundleVundlevim

callvundlebegin()

letVundlemanageVundlerequired

PlugingmarikVundlevim

AllofyourPluginsmustbeaddedbeforethefollowingline

callvundleend()required

filetypepluginindentonrequired

2InstallVim-go

Edit~vimrcAddalinebetweenvundlebeginandvundleend

Pluginfatihvim-go

ExecutedwithinVimPluginInstall

3InstallYCM(YourCompleteMe)toAutoCompleteAddalineto~vimrc

PluginValloricYouCompleteMe

Figure18VimintelligentcompletionforGo

1 SyntaxhighlightingforGo

cp-r$GOROOTmiscvim~vim

2 Enablingsyntaxhighlighting

filetypepluginindenton

syntaxon

3 Installgocode

gocodewillbeinstalledin$GOBINasdefault

Godevelopmenttools

4 Configuregocode

~cd$GOPATHsrcgithubcomnsfgocodevim

~updatesh

~gocodesetpropose-builtinstrue

propose-builtinstrue

~gocodesetlib-pathhomebordergocodepkglinux_amd64

lib-pathhomebordergocodepkglinux_amd64

~gocodeset

Explanationofgocodeconfiguration

propose-builtinsspecifieswhetherornottoopenintelligentcompletionfalsebydefaultlib-pathgocodeonlysearchesforpackagesin$GOPATHpkg$GOOS_$GOARCHand$GOROOTpkg$GOOS_$GOARCHThissettingcanbeusedtoaddadditionalpaths

5 CongratulationsTryemaingotoexperiencetheworldofGo

EmacsEmacsistheso-calledWeaponofGodSheisnotonlyaneditorbutalsoapowerfulIDE

Figure110EmacsmainpanelofGoeditor

1 Syntaxhighlighting

cp$GOROOTmiscemacs~emacsd

2 Installgocode

3 Configuregocode

~updatebash

~gocodeset

4 InstallAutoCompletionDownloadanduncompress

~makeinstallDIR=$HOMEemacsdauto-complete

Configure~emacsfile

Godevelopmenttools

auto-complete

(requireauto-complete-config)

(add-to-listac-dictionary-directories~emacsdauto-completeac-dict)

(ac-config-default)

(local-set-key(kbdM-)semantic-complete-analyze-inline)

(local-set-keysemantic-complete-self-insert)

(local-set-keygtsemantic-complete-self-insert)

Followthislinkformoredetails

5 Configureemacs

golangmode

(requirego-mode-load)

(requirego-autocomplete)

speedbar

(speedbar1)

(speedbar-add-supported-extensiongo)

(add-hook

go-mode-hook

(lambda()

gocode

(auto-complete-mode1)

(setqac-sources(ac-source-go))

ImenuampSpeedbar

(setqimenu-generic-expression

((type^type([^tnrf])1)

(func^func()1)))

(imenu-add-to-menubarIndex)

Outlinemode

(make-local-variableoutline-regexp)

(outline-minor-mode1)

(local-set-keyM-aoutline-previous-visible-heading)

(local-set-keyM-eoutline-next-visible-heading)

Menubar

(requireeasymenu)

(defconstgo-hooked-menu

(Gotools

[Gorunbuffergot]

[Goreformatbuffergo-fmt-buffert]

[Gocheckbuffergo-fix-buffert]))

(easy-menu-define

go-added-menu

(current-local-map)

Gotools

go-hooked-menu)

(setqshow-trailing-whitespacet)

helperfunction

(defungo()

runcurrentbuffer

(interactive)

(compile(concatgorun(buffer-file-name))))

helperfunction

(defungo-fmt-buffer()

rungofmtoncurrentbuffer

(interactive)

(ifbuffer-read-only

(progn

(ding)

(messageBufferisreadonly))

(let((p(line-number-at-pos))

(filename(buffer-file-name))

(old-max-mini-window-heightmax-mini-window-height))

(show-all)

(if(get-bufferGoReformatErrors)

Godevelopmenttools

(progn

(delete-windows-onGoReformatErrors)

(kill-bufferGoReformatErrors)))

(setqmax-mini-window-height1)

(if(=0(shell-command-on-region(point-min)(point-max)gofmtGoReformatOutputnilGoRefor

matErrorst))

(progn

(erase-buffer)

(insert-buffer-substringGoReformatOutput)

(goto-char(point-min))

(forward-line(1-p)))

(with-current-bufferGoReformatErrors

(progn

(while(re-search-forwardltstandardinputgtnilt)

(replace-matchfilename))

(compilation-mode))))

(setqmax-mini-window-heightold-max-mini-window-height)

(delete-windows-onGoReformatOutput)

(kill-bufferGoReformatOutput))))

helperfunction

(defungo-fix-buffer()

rungofixoncurrentbuffer

(interactive)

(show-all)

(shell-command-on-region(point-min)(point-max)gotoolfix-diff))

6 CongratulationsyouredoneSpeedbarisclosedbydefault-removethecommentsymbolsintheline(speedbar1)toenablethisfeatureoryoucanuseitthroughM-xspeedbar

EclipseEclipseisalsoagreatdevelopmenttoolIllshowyouhowtouseittowriteGoprograms

Figure11EclipsemainpanelforeditingGo

1 DownloadandinstallEclipse2 DownloadgoclipsehttpcodegooglecompgoclipsewikiInstallationInstructions3 Downloadgocode

gocodeinGithub

httpsgithubcomnsfgocode

YouneedtoinstallgitinWindowsusuallyweusemsysgit

Installgocodeinthecommandtool

Youcaninstallfromsourcecodeifyoulike

4 DownloadandinstallMinGW5 Configureplugins

Windows-gtPreferences-gtGo

(1)ConfigureGocompiler

Godevelopmenttools

Figure112GoSettinginEclipse

(2)Configuregocode(optional)setgocodepathtowherethegocodeexeis

Figure113gocodeSetting

(3)Configuregdb(optional)setgdbpathtowherethegdbexeis

Figure114gdbSetting

6 Checktheinstallation

CreateanewGoprojectandhellogofileasfollowing

Figure115Createanewprojectandfile

Testinstallationasfollows(youneedtotypecommandinconsoleinEclipse)

Figure116TestGoprograminEclipse

IntelliJIDEAPeoplewhohaveworkedwithJavashouldbefamiliarwiththisIDEItsupportsGosyntaxhighlightingandintelligentcodecompletionimplementedbyaplugin

1 DownloadIDEAthereisnodifferencebetweentheUltimateandCommunityeditions

2 InstalltheGopluginChooseFile-Setting-PluginsthenclickBrowserrepo

3 Searchgolangdoubleclickdownloadandinstallandwaitforthedownloadtocomplete

ClickApplythenrestart

4 NowyoucancreateaGoproject

InputthepositionofyourGosdkinthenextstep-basicallyitsyour$GOROOT

(SeeablogpostforsetupanduseIntelliJIDEAwithGostepbystep)

VisualStudioVSCodeThisisanawesometexteditorreleasedasopensourcecrossplatformmyMicrosoftwhichtakesthedevelopmentexperiencetoawholenewlevelhttpscodevisualstudiocomIthaseverythingamoderntexteditorisexpectedtohaveanddespitebeingbasedonthesamebackendthatatomioisbaseditisveryfast

ItworkswithWindowsMacLinuxIthasgopackagebuiltitprovidescodelinting

Godevelopmenttools

AtomAtomisanawesometexteditorreleasedasopensourcecrossplatformbuiltonElectronandbasedoneverythingweloveaboutourfavoriteeditorsWedesignedittobedeeplycustomizablebutstillapproachableusingthedefaultconfiguration

Downloadhttpsatomio

GoglandGoglandisthecodenameforanewcommercialIDEbyJetBrainsaimedatprovidinganergonomicenvironmentforGodevelopment

Theofficialversionisnotyetreleased

Downloadhttpswwwjetbrainscomgo

LinksDirectoryPrevioussectionGocommandsNextsectionSummary

Godevelopmenttools

15SummaryInthischapterwetalkedabouthowtoinstallGousingthreedifferentmethodsincludingfromsourcecodethestandardpackageandviathird-partytoolsThenweshowedyouhowtoconfiguretheGodevelopmentenvironmentmainlycoveringhowtosetupyour$GOPATHAfterthatweintroducedsomestepsforcompilinganddeployingGoprogramsWethencoveredGocommandsincludingthecompileinstallformatandtestcommandsFinallytherearemanypowerfultoolstodevelopGoprogramssuchasLiteIDESublimeTextVSCodeAtomGoglangVimEmacsEclipseIntelliJIDEAetcYoucanchooseanyoneyoulikeexploringtheworldofGo

LinksDirectoryPrevioussectionGodevelopmenttoolsNextchapterGobasicknowledge

Summary

2GobasicknowledgeGoisacompiledsystemprogramminglanguageanditbelongstotheC-familyHoweveritscompilationspeedismuchfasterthanotherC-familylanguagesIthasonly25keywordsevenlessthanthe26lettersoftheEnglishalphabetLetstakealookatthesekeywordsbeforewegetstarted

breakdefaultfuncinterfaceselect

casedefergomapstruct

chanelsegotopackageswitch

constfallthroughifrangetype

continueforimportreturnvar

InthischapterImgoingtoteachyousomebasicGoknowledgeYouwillfindouthowconcisetheGoprogramminglanguageisandthebeautifuldesignofthelanguageProgrammingcanbeveryfuninGoAfterwecompletethischapteryoullbefamiliarwiththeabovekeywords

LinksDirectoryPreviouschapterChapter1SummaryNextsectionHelloGo

Gobasicknowledge

WhatmakesGodifferentfromotherlanguagesTheGoprogramminglanguagewascreatedwithonegoalinmindtobeabletobuildscalableweb-applicationsforlargescaleaudiencesinalargeteamSothatisthereasontheymadethelanguageasstandardizedaspossiblehencethegofmttoolandthestrictusageguidelinestothelanguagewasforthesakeofnothavingtwofactionsinthedeveloperbaseinotherlanguagestherearereligiouswarsonwheretokeeptheopeningbrace

publicstaticvoidmain()

orforpythonshouldweuse4spacesor6spacesoratabortwotabsandotheruserpreferencesIfyouknowpythonthenyoumightbeawareofPEP8whichisasetofguidelinesabouthowtowriteelegantcode

WhilethismightseemtobeashallowproblemwhenthecodebasegrowsandmoreandmorepeopleworkonthesamecodebaseitisbecomesincreasinglydifficulttomaintainthecodesbeautyWeliveinaworldwhererobotscandriveacarsoweshouldntjustwritecodeweshouldwriteelegantcode

ForotherlanguagestherearemanyvariableswhenitcomestowritingcodeEverylanguageisgoodforitsusecasebutGoisalittlespecialbecauseitwasdesignedatacompanywhichistheverysynonymoftheInternet(anddistributedcomputing)TypicallyinordertooptimizeprogramsdeveloperschoosetowriteJavaoverPythonandC++overJavabutalmostallavailablelanguageswidelyinusewerewrittendecadesagowhen1GBstoragewasmuchpricierNowstorageandcomputingisrelativelycheapandcomputersaregettingmultiplescoresbuttheoldlanguagesarenotharnessingconcurrencyinawaythatgodoesItsnotbecausethoselanguagesarebadutilizingconcurrencywasntarelevantusecasewhiletheolderlanguagesevolved

TomitigatealltheproblemsthatGooglefacedwithcurrenttoolstheywroteasystemslanguagecalledGowhichyouareabouttolearnTherearemanyadvantagestousinggolangandtherearedisadvantagestooforeverycoinhasbothsidesOneofthesignificantimprovementsinincodeformattingGooglehasdesignedthelanguagetoavoiddebatesoncodeformattingGocodewrittenbyanyoneintheworld(assumingtheyknowandusegofmt)willlookexactlythesameThiswontseemtomatteruntilyouworkinateamAlsowhenthecompanyusesautomatedcoderevieworsomeotherfancytechniquetheformattedcodemaybreakinotherlanguageswhichdonthavestrictandstandardformattingrulesbutnotingo

Gowasdesignedwithconcurrencyinmindpleasenotethatparallelism=concurrencythereisanamazingpostbyRobPikeonthegolangblogyouwillfinditthereitiswortharead

AnotherveryimportantchangethatistheconceptofGOPATHGonearethedayswhenyouhadtocreateafoldercalledcodeandthencreateworkspacesforeclipseandwhatnotNowyouhavetokeeponefoldertreeforgocodewhichwillbeupdatedbythepackagemanagerautomaticallyItisalsorecommendedtocreatefolderswitheitheracustomdomainorthegithubdomainforexampleIcreatedataskmanagerusinggolangsoIcreatedasetoffolders~gosrcgithubcomthewhitetulipTasks

NoteInnixsystems~standsforhomedirectorywhichisthewindowsequivalentofCUsersusernameNowthe~goistheuniverseforthegocodeinyourmachineThisisasignificantimprovementoverotherlanguageswecanstorethecodeefficientlywithouthasslesWhileitmightseemstrangeatfirstthisapproachmakealotofsensethantheridiculouspackagenamesiepackagenamesgeneratedforotherlanguagesusingreversedomains

NoteAlongwithsrctherearetwofolderspkgwhichisforpackagesandbinwhichisforbinary

HelloGo

ThisGOPATHadvantageisntjustrestrictedtostoringcodeinparticularfolderWhenyouhavecreatedfivepackagesforyourprojectyoudonthavetoimportthemlikeimportdbInsteadyoucanuseimportgithubcomthewhitetulipTasksdbsothatwhenexecutinggogetonmyrepothegotoolwillfindthepackagefromgithubcompathifitwasntdownloadedinitiallyThisstandardizesalotofscrewedupthingsintheprogrammingdiscipline(lt--Toremoveandreplacewithactualexplanationofwhythisisbetter)

Whiletheremaybesomefoundedcomplaintsthatgocreatorshaveignoredalllanguageresearchdonesincethepast30yrsyoucannotcreateaproductoralanguagewhicheveryonewillfallinlovewithTherearealwayssomeortheotherusecasesorconstraintswhichthecreatorsshouldconsiderConsideringalltheadvantagesatleastforwebdevelopmentIdonotthinkanylanguagegetsclosetotheadvantageswhichgohasevenifyouignoreallthatIsaidaboveGoisacompiledlanguagewhichmeansinproductionyouwonthavetosetupaJVMoravirtualenvandwillinsteadhaveasinglestaticbinaryLikeanicingonacakeallthemodernlibrariesareinthestandardlibrarysuchasthehttpliballowingyoutocreatewebappsingolangwithoutusingathirdpartywebframework

21HelloGoBeforewestartbuildinganapplicationinGoweneedtolearnhowtowriteasimpleprogramYoucantexpecttobuildabuildingwithoutfirstknowinghowtobuilditsfoundationThereforewearegoingtolearnthebasicsyntaxtorunsomesimpleprogramsinthissection

ProgramAccordingtointernationalpracticebeforeyoulearnhowtoprograminsomelanguagesyouwillwanttoknowhowtowriteaprogramtoprintHelloworld

AreyoureadyLetsGo

packagemain

importfmt

funcmain()

fmtPrintf(Helloworldor你好世界orΚαλημέρακόσμεorこんにちは世界n)

Itprintsfollowinginformation

Helloworldor你好世界orΚαλημέρακόσμεorこんにちは世界

ExplanationOnethingthatyoushouldknowinthefirstisthatGoprogramsarecomposedbypackage

packageltpkgNamegt(Inthiscaseispackagemain)tellsusthissourcefilebelongstomainpackageandthekeywordmaintellsusthispackagewillbecompiledtoaprograminsteadofpackagefileswhoseextensionsarea

Everyexecutableprogramhasoneandonlyonemainpackageandyouneedanentryfunctioncalledmainwithoutanyargumentsorreturnvaluesinthemainpackage

InordertoprintHelloworldhellipwecalledafunctioncalledPrintfThisfunctioniscomingfromfmtpackagesoweimportthispackageinthethirdlineofsourcecodewhichisimportfmt

ThewaytothinkaboutpackagesinGoissimilartoPythonandtherearesomeadvantagesModularity(breakupyourprogramintomanymodules)andreusability(everymodulecanbereusedinmanyprograms)Wejusttalkedaboutconceptsregardingpackagesandwewillmakeourownpackageslater

HelloGo

OnthefifthlineweusethekeywordfunctodefinethemainfunctionThebodyofthefunctionisinsideofjustlikeCC++andJava

AsyoucanseetherearenoargumentsWewilllearnhowtowritefunctionswithargumentsinjustasecondandyoucanalsohavefunctionsthathavenoreturnvalueorhaveseveralreturnvalues

OnthesixthlinewecalledthefunctionPrintfwhichisfromthepackagefmtThiswascalledbythesyntaxltpkgNamegtltfuncNamegtwhichisverylikePython-style

Aswementionedinchapter1thepackagesnameandthenameofthefolderthatcontainsthatpackagecanbedifferentHeretheltpkgNamegtcomesfromthenameinpackageltpkgNamegtnotthefoldersname

Youmaynoticethattheexampleabovecontainsmanynon-ASCIIcharactersThepurposeofshowingthisistotellyouthatGosupportsUTF-8bydefaultYoucanuseanyUTF-8characterinyourprograms

EachgofileisinsomepackageandthatpackageshouldbeadistinctfolderintheGOPATHbutmainisaspecialpackagewhichdoesntrequireamainfolderThisisoneaspectwhichtheyleftoutforstandardizationButshouldyouchoosetomakeamainfolderthenyouhavetoensurethatyourunthebinaryproperlyAlsoonegocodecanthavemorethanonemaingofile

~gosrcgithubcomthewhitetulipTasksmain$gobuild~gosrcgithubcomthewhitetulipTasks$mainmain

thethinghereisthatwhenyourcodeisusingsomestaticfilesorsomethingelsethenyououghttorunthebinaryfromtherootoftheapplicationasweseeinthesecondlineaboveIamrunningthemainbinaryoutsidethemainpackagesometimesyoumightwonderwhyyourapplicationisntworkingthenthismightbeoneofthepossibleproblemspleasekeepthisinmind

Onethingyouwillnoticehereisthatgodoesntseetousesemicolonstoendastatementwellitdoesjustthereisaminorcatchtheprogrammerisntexpectedtoputsemicolonsthecompileraddssemicolonstothegocodewhenitcompileswhichisthereasonthatthis(thankfully)isasyntaxerror

funcmain()

becausethecompileraddsasemicolonattheendofmain()whichisasyntaxerrorandasstatedaboveithelpsavoidreligiouswarsiwishtheycombinevimandemacsandcreateauniversaleditorwhichllhelpsavesomemorewarsButfornowwelllearnGo

ConclusionGousespackage(likemodulesinPython)toorganizeprogramsThefunctionmainmain()(thisfunctionmustbeinthemainpackage)istheentrypointofanyprogramGostandardizeslanguageandmostoftheprogrammingmethodologysavingtimeofdeveloperswhichtheydhavewastedinreligiouswarsTherecanbeonlyonemainpackageandonlyonemainfunctioninsideagomainpackageGosupportsUTF-8charactersbecauseoneofthecreatorsofGoisacreatorofUTF-8soGohassupportedmultiplelanguagesfromthetimeitwasborn

LinksDirectoryPrevioussectionGobasicknowledgeNextsectionGofoundation

HelloGo

22GofoundationInthissectionwearegoingtoteachyouhowtodefineconstantsvariableswithelementarytypesandsomeskillsinGoprogramming

DefinevariablesTherearemanyformsofsyntaxthatcanbeusedtodefinevariablesinGo

ThekeywordvaristhebasicformtodefinevariablesnoticethatGoputsthevariabletypeafterthevariablename

defineavariablewithnameldquovariableNamerdquoandtypetype

varvariableNametype

Definemultiplevariables

definethreevariableswhichtypesaretype

varvname1vname2vname3type

Defineavariablewithinitialvalue

defineavariablewithnameldquovariableNamerdquotypetypeandvaluevalue

varvariableNametype=value

Definemultiplevariableswithinitialvalues

Definethreevariableswithtypetypeandinitializetheirvalues

vname1isv1vname2isv2vname3isv3

varvname1vname2vname3type=v1v2v3

DoyouthinkthatitstootedioustodefinevariablesusethewayaboveDontworrybecausetheGoteamhasalsofoundthistobeaproblemThereforeifyouwanttodefinevariableswithinitialvalueswecanjustomitthevariabletypesothecodewilllooklikethisinstead

Definethreevariableswithouttypetypeandinitializetheirvalues

varvname1vname2vname3=v1v2v3

WellIknowthisisstillnotsimpleenoughforyouLetsseehowwefixit

Definethreevariableswithouttypetypeandwithoutkeywordvarandinitializetheirvalues

vname1vname2vname3=v1v2v3

NowitlooksmuchbetterUse=toreplacevarandtypethisiscalledashortassignmentIthasonelimitationthisformcanonlybeusedinsideofafunctionsYouwillgetcompileerrorsifyoutrytouseitoutsideoffunctionbodiesThereforeweusuallyusevartodefineglobalvariables

Gofoundation

_(blank)isaspecialvariablenameAnyvaluethatisgiventoitwillbeignoredForexamplewegive35tobanddiscard34(ThisexamplejustshowyouhowitworksItlooksuselessherebecauseweoftenusethissymbolwhenwegetfunctionreturnvalues)

_b=3435

IfyoudontusevariablesthatyouvedefinedinyourprogramthecompilerwillgiveyoucompilationerrorsTrytocompilethefollowingcodeandseewhathappens

packagemain

funcmain()

variint

ConstantsSo-calledconstantsarethevaluesthataredeterminedduringcompiletimeandyoucannotchangethemduringruntimeInGoyoucanusenumberbooleanorstringastypesofconstants

Defineconstantsasfollows

constconstantName=value

youcanassigntypeofconstantsifitsnecessary

constPifloat32=31415926

Moreexamples

constPi=31415926

consti=10000

constMaxThread=10

constprefix=astaxie_

Elementarytypes

Boolean

InGoweusebooltodefineavariableasbooleantypethevaluecanonlybetrueorfalseandfalsewillbethedefaultvalue(Youcannotconvertvariablestypebetweennumberandboolean)

samplecode

varisActiveboolglobalvariable

varenableddisabled=truefalseomittypeofvariables

functest()

varavailableboollocalvariable

valid=falsebriefstatementofvariable

available=trueassignvaluetovariable

Numericaltypes

IntegertypesincludebothsignedandunsignedintegertypesGohasintanduintatthesametimetheyhavesamelengthbutspecificlengthdependsonyouroperatingsystemTheyuse32-bitin32-bitoperatingsystemsand64-bitin64-bitoperatingsystemsGoalsohastypesthathavespecificlengthincludingruneint8int16int32int64byteuint8uint16uint32uint64Notethatruneisaliasofint32andbyteisaliasofuint8

Gofoundation

Oneimportantthingyoushouldknowthatyoucannotassignvaluesbetweenthesetypesthisoperationwillcausecompileerrors

varaint8

varbint32

Althoughint32hasalongerlengththanint8andhasthesametypeasintyoucannotassignvaluesbetweenthem(cwillbeassertedastypeinthere)

Floattypeshavethefloat32andfloat64typesandnotypecalledfloatThelatteroneisthedefaulttypeifusingbriefstatement

ThatsallNoGosupportscomplexnumbersaswellcomplex128(witha64-bitrealand64-bitimaginarypart)isthedefaulttypeifyouneedasmallertypethereisonecalledcomplex64(witha32-bitrealand32-bitimaginarypart)ItsformisRE+IMiwhereREisrealpartandIMisimaginarypartthelastiistheimaginarynumberThereisaexampleofcomplexnumber

varccomplex64=5+5i

output(5+5i)

fmtPrintf(Valueisvc)

String

WejusttalkedabouthowGousestheUTF-8charactersetStringsarerepresentedbydoublequotesorbackticks `

samplecode

varfrenchHellostringbasicformtodefinestring

varemptyStringstring=defineastringwithemptystring

functest()

noyesmaybe=noyesmaybebriefstatement

japaneseHello=Ohaiou

frenchHello=Bonjourbasicformofassignvalues

ItsimpossibletochangestringvaluesbyindexYouwillgeterrorswhenyoucompilethefollowingcode

varsstring=hello

s[0]=c

WhatifIreallywanttochangejustonecharacterinastringTrythefollowingcode

s=hello

c=[]byte(s)convertstringto[]bytetype

c[0]=c

s2=string(c)convertbacktostringtype

fmtPrintf(sns2)

Youusethe+operatortocombinetwostrings

s=hello

m=world

fmtPrintf(sna)

andalso

Gofoundation

s=hello

s=c+s[1]youcannotchangestringvaluesbyindexbutyoucangetvaluesinstead

fmtPrintf(sns)

WhatifIwanttohaveamultiple-linestring

m=`hello

world`

willnotescapeanycharactersinastring

ErrortypesGohasoneerrortypeforpurposeofdealingwitherrormessagesThereisalsoapackagecallederrorstohandleerrors

err=errorsNew(emitmachodwarfelfheadercorrupted)

iferr=nil

fmtPrint(err)

Underlyingdatastructure

ThefollowingpicturecomesfromanarticleaboutGodatastructureinRussCoxsBlogAsyoucanseeGoutilizesblocksofmemorytostoredata

Figure21Gounderlyingdatastructure

Someskills

Definebygroup

Ifyouwanttodefinemultipleconstantsvariablesorimportpackagesyoucanusethegroupform

Basicform

importfmt

importos

consti=100

constpi=31415

constprefix=Go_

variint

varpifloat32

varprefixstring

Groupform

Gofoundation

import(

const(

pi=31415

prefix=Go_

pifloat32

prefixstring

Unlessyouassignthevalueofconstantisiotathefirstvalueofconstantinthegroupconst()willbe0IffollowingconstantsdontassignvaluesexplicitlytheirvalueswillbethesameasthelastoneIfthevalueoflastconstantisiotathevaluesoffollowingconstantswhicharenotassignedareiotaalso

iotaenumerate

Gohasonekeywordcallediotathiskeywordistomakeenumitbeginswith0increasedby1

const(

x=iotax==0

y=iotay==1

z=iotaz==2

wIfthereisnoexpressionaftertheconstantsnameitusesthelastexpression

soitssayingw=iotaimplicitlyThereforew==3andyandzbothcanomit=iotaaswell

constv=iotaonceiotameetskeyword`const`itresetsto`0`sov=0

const(

efg=iotaiotaiotae=0f=0g=0valuesofiotaaresameinoneline

Somerules

ThereasonthatGoisconcisebecauseithassomedefaultbehaviors

AnyvariablethatbeginswithacapitallettermeansitwillbeexportedprivateotherwiseThesameruleappliesforfunctionsandconstantsnopublicorprivatekeywordexistsinGo

arrayslicemap

arrayisanarrayobviouslywedefineoneasfollows

vararr[n]type

in[n]typenisthelengthofthearraytypeisthetypeofitselementsLikeotherlanguagesweuse[]togetorsetelementvalueswithinarrays

Gofoundation

vararr[10]intanarrayoftype[10]int

arr[0]=42arrayis0-based

arr[1]=13assignvaluetoelement

fmtPrintf(Thefirstelementisdnarr[0])

getelementvalueitreturns42

fmtPrintf(Thelastelementisdnarr[9])

itreturnsdefaultvalueof10thelementinthisarraywhichis0inthiscase

Becauselengthisapartofthearraytype[3]intand[4]intaredifferenttypessowecannotchangethelengthofarraysWhenyouusearraysasargumentsfunctionsgettheircopiesinsteadofreferencesIfyouwanttousereferencesyoumaywanttousesliceWelltalkaboutlater

Itspossibletouse=whenyoudefinearrays

a=[3]int123defineanintarraywith3elements

b=[10]int123

defineaintarraywith10elementsofwhichthefirstthreeareassigned

Therestofthemusethedefaultvalue0

c=[]int456use`hellip`toreplacethelengthparameterandGowillcalculateitforyou

YoumaywanttousearraysasarrayselementsLetsseehowtodothis

defineatwo-dimensionalarraywith2elementsandeachelementhas4elements

doubleArray=[2][4]int[4]int1234[4]int5678

Thedeclarationcanbewrittenmoreconciselyasfollows

easyArray=[2][4]int12345678

Arrayunderlyingdatastructure

Figure22Multidimensionalarraymappingrelationship

sliceInmanysituationsthearraytypeisnotagoodchoice-forinstancewhenwedontknowhowlongthearraywillbewhenwedefineitThusweneedadynamicarrayThisiscalledsliceinGo

sliceisnotreallyadynamicarrayItsareferencetypeslicepointstoanunderlyingarraywhosedeclarationissimilartoarraybutdoesntneedlength

justlikedefininganarraybutthistimeweexcludethelength

varfslice[]int

Thenwedefineasliceandinitializeitsdata

slice=[]byteabcd

slicecanredefineexistingslicesorarrayssliceusesarray[ij]toslicewhereiisthestartindexandjisendindexbutnoticethatarray[j]willnotbeslicedsincethelengthofthesliceisj-i

Gofoundation

defineanarraywith10elementswhosetypesarebytes

varar=[10]byteabcdefghij

definetwosliceswithtype[]byte

varab[]byte

apointstoelementsfrom3rdto5thinarrayar

a=ar[25]

nowahaselementsar[2]ar[3]andar[4]

bisanothersliceofarrayar

b=ar[35]

nowbhaselementsar[3]andar[4]

NoticethedifferencesbetweensliceandarraywhenyoudefinethemWeuse[hellip]toletGocalculatelengthbutuse[]todefinesliceonly

Theirunderlyingdatastructure

Figure23Correspondencebetweensliceandarray

slicehassomeconvenientoperations

sliceis0-basedar[n]equalstoar[0n]Thesecondindexwillbethelengthofsliceifomittedar[n]equalstoar[nlen(ar)]Youcanusear[]toslicewholearrayreasonsareexplainedinfirsttwostatements

Moreexamplespertainingtoslice

defineanarray

vararray=[10]byteabcdefghij

definetwoslices

varaSlicebSlice[]byte

someconvenientoperations

aSlice=array[3]equalstoaSlice=array[03]aSlicehaselementsabc

aSlice=array[5]equalstoaSlice=array[510]aSlicehaselementsfghij

aSlice=array[]equalstoaSlice=array[010]aSlicehasallelements

slicefromslice

aSlice=array[37]aSlicehaselementsdefglen=4cap=7

bSlice=aSlice[13]bSlicecontainsaSlice[1]aSlice[2]soithaselementsef

bSlice=aSlice[3]bSlicecontainsaSlice[0]aSlice[1]aSlice[2]soithasdef

bSlice=aSlice[05]slicecouldbeexpandedinrangeofcapnowbSlicecontainsdefgh

bSlice=aSlice[]bSlicehassameelementsasaSlicedoeswhicharedefg

sliceisareferencetypesoanychangeswillaffectothervariablespointingtothesamesliceorarrayForinstanceinthecaseofaSliceandbSliceaboveifyouchangethevalueofanelementinaSlicebSlicewillbechangedaswell

sliceislikeastructbydefinitionanditcontains3parts

ApointerthatpointstowhereslicestartsThelengthofsliceCapacitythelengthfromstartindextoendindexofslice

Array_a=[10]byteabcdefghij

Slice_a=Array_a[25]

Theunderlyingdatastructureofthecodeaboveasfollows

Gofoundation

Figure24Arrayinformationofslice

Therearesomebuilt-infunctionsforslice

lengetsthelengthofslicecapgetsthemaximumlengthofsliceappendappendsoneormoreelementstosliceandreturnsslicecopycopieselementsfromoneslicetotheotherandreturnsthenumberofelementsthatwerecopied

AttentionappendwillchangethearraythatslicepointstoandaffectotherslicesthatpointtothesamearrayAlsoifthereisnotenoughlengthfortheslice((cap-len)==0)appendreturnsanewarrayforthissliceWhenthishappensotherslicespointingtotheoldarraywillnotbeaffected

mapbehaveslikeadictionaryinPythonUsetheformmap[keyType]valueTypetodefineit

LetsseesomecodeThesetandgetvaluesinmaparesimilartoslicehowevertheindexinslicecanonlybeoftypeintwhilemapcanusemuchmorethanthatforexampleintstringorwhateveryouwantAlsotheyareallabletouse==and=tocomparevalues

usestringasthekeytypeintasthevaluetypeand`make`initializeit

varnumbersmap[string]int

anotherwaytodefinemap

numbers=make(map[string]int)

numbers[one]=1assignvaluebykey

numbers[ten]=10

numbers[three]=3

fmtPrintln(Thethirdnumberisnumbers[three])getvalues

ItprintsThethirdnumberis3

Somenoteswhenyouusemap

mapisdisorderlyEverytimeyouprintmapyouwillgetdifferentresultsItsimpossibletogetvaluesbyindex-youhavetousekeymapdoesnthaveafixedlengthItsareferencetypejustlikeslicelenworksformapalsoItreturnshowmanykeysthatmaphasItsquiteeasytochangethevaluethroughmapSimplyusenumbers[one]=11tochangethevalueofkeyoneto11

Youcanuseformkeyvaltoinitializemapsvaluesandmaphasbuilt-inmethodstocheckifthekeyexists

Usedeletetodeleteanelementinmap

Initializeamap

rating=map[string]float32C5Go45Python45C++2

maphastworeturnvaluesForthesecondreturnvalueifthekeydoesnt

existokreturnsfalseItreturnstrueotherwise

csharpRatingok=rating[C]

fmtPrintln(CisinthemapanditsratingiscsharpRating)

fmtPrintln(WehavenoratingassociatedwithCinthemap)

delete(ratingC)deleteelementwithkeyc

AsIsaidabovemapisareferencetypeIftwomapspointtosameunderlyingdataanychangewillaffectbothofthem

Gofoundation

m=make(map[string]string)

m[Hello]=Bonjour

m1[Hello]=Salutnowthevalueofm[hello]isSalut

makenewmakedoesmemoryallocationforbuilt-inmodelssuchasmapsliceandchannelwhilenewisfortypesmemoryallocation

new(T)allocateszero-valuetotypeTsmemoryreturnsitsmemoryaddresswhichisthevalueoftypeTByGosdefinitionitreturnsapointerwhichpointstotypeTszero-value

newreturnspointers

Thebuilt-infunctionmake(Targs)hasdifferentpurposesthannew(T)makecanbeusedforslicemapandchannelandreturnsatypeTwithaninitialvalueThereasonfordoingthisisbecausetheunderlyingdataofthesethreetypesmustbeinitializedbeforetheypointtothemForexampleaslicecontainsapointerthatpointstotheunderlyingarraylengthandcapacityBeforethesedataareinitializedsliceisnilsoforslicemapandchannelmakeinitializestheirunderlyingdataandassignssomesuitablevalues

makereturnsnon-zerovalues

Thefollowingpictureshowshownewandmakearedifferent

Figure25Underlyingmemoryallocationofmakeandnew

Zero-valuedoesnotmeanemptyvalueItsthevaluethatvariablesdefaulttoinmostcasesHereisalistofsomezero-values

int320

int640

uint0x0

rune0theactualtypeofruneisint32

byte0x0theactualtypeofbyteisuint8

float320lengthis4byte

boolfalse

string

LinksDirectoryPrevioussectionHelloGoNextsectionControlstatementsandfunctions

Gofoundation

23ControlstatementsandfunctionsInthissectionwearegoingtotalkaboutcontrolstatementsandfunctionoperationsinGo

ControlstatementThegreatestinventioninprogrammingisflowcontrolBecauseofthemyouareabletousesimplecontrolstatementsthatcanbeusedtorepresentcomplexlogicTherearethreecategoriesofflowcontrolconditionalcyclecontrolandunconditionaljump

ifwillmostlikelybethemostcommonkeywordinyourprogramsIfitmeetstheconditionsthenitdoessomethinganditdoessomethingelseifnot

ifdoesntneedparenthesesinGo

ifxgt10

fmtPrintln(xisgreaterthan10)

fmtPrintln(xislessthanorequalto10)

ThemostusefulthingconcerningifinGoisthatitcanhaveoneinitializationstatementbeforetheconditionalstatementThescopeofthevariablesdefinedinthisinitializationstatementareonlyavailableinsidetheblockofthedefiningif

initializexthencheckifxgreaterthan

ifx=computedValue()xgt10

fmtPrintln(xislessthan10)

thefollowingcodewillnotcompile

fmtPrintln(x)

Useif-elseformultipleconditions

ifinteger==3

fmtPrintln(Theintegerisequalto3)

elseifintegerlt3

fmtPrintln(Theintegerislessthan3)

fmtPrintln(Theintegerisgreaterthan3)

gotoGohasagotokeywordbutbecarefulwhenyouuseitgotoreroutesthecontrolflowtoapreviouslydefinedlabelwithinthebodyofsamecodeblock

funcmyFunc()

Herelabelendswith

fmtPrintln(i)

gotoHerejumptolabelHere

Thelabelnameiscasesensitive

foristhemostpowerfulcontrollogicinGoItcanreaddatainloopsanditerativeoperationsjustlikewhile

forexpression1expression2expression3

expression1expression2andexpression3areallexpressionswhereexpression1andexpression3arevariabledefinitionsorreturnvaluesfromfunctionsandexpression2isaconditionalstatementexpression1willbeexecutedoncebeforeloopingandexpression3willbeexecutedaftereachloop

Examplesaremoreusefulthanwords

packagemain

importfmt

funcmain()

forindex=0indexlt10index++

sum+=index

fmtPrintln(sumisequaltosum)

Printsumisequalto45

SometimesweneedmultipleassignmentsbutGodoesnthavetheoperatorsoweuseparallelassignmentlikeij=i+1j-1

Wecanomitexpression1andexpression3iftheyarenotnecessary

forsumlt1000

sum+=sum

OmitaswellFeelfamiliarYesitsidenticaltowhile

forsumlt1000

sum+=sum

TherearetwoimportantoperationsinloopswhicharebreakandcontinuebreakjumpsoutoftheloopandcontinueskipsthecurrentloopandstartsthenextoneIfyouhavenestedloopsusebreakalongwithlabels

forindex=10indexgt0index--

ifindex==5

breakorcontinue

fmtPrintln(index)

breakprints109876

continueprints1098764321

forcanreaddatafromarrayslicemapandstringwhenitisusedtogetherwithrange

forkv=rangemap

fmtPrintln(mapskeyk)

fmtPrintln(mapsvalv)

BecauseGosupportsmulti-valuereturnsandgivescompileerrorswhenyoudontusevaluesthatweredefinedyoumaywanttouse_todiscardcertainreturnvalues

for_v=rangemap

Withgoyoucanaswellcreateaninfiniteloopwhichisequivalenttowhiletrueinotherlanguges

yourlogic

switchSometimesyoumayfindthatyouareusingtoomanyif-elsestatementstoimplementsomelogicwhichmaymakeitdifficulttoreadandmaintaininthefutureThisistheperfecttimetousetheswitchstatementtosolvethisproblem

switchsExpr

caseexpr1

someinstructions

caseexpr2

someotherinstructions

caseexpr3

default

othercode

ThetypeofsExprexpr1expr2andexpr3mustbethesameswitchisveryflexibleConditionsdonthavetobeconstantsanditexecutesfromtoptobottomuntilitmatchesconditionsIfthereisnostatementafterthekeywordswitchthenitmatchestrue

switchi

fmtPrintln(iisequalto1)

case234

fmtPrintln(iisequalto23or4)

case10

default

fmtPrintln(AllIknowisthatiisaninteger)

InthefifthlineweputmanyvaluesinonecaseandwedontneedtoaddthebreakkeywordattheendofcasesbodyItwilljumpoutoftheswitchbodyonceitmatchedanycaseIfyouwanttocontinuetomatchingmorecasesyouneedtousethefallthroughstatement

integer=6

switchinteger

fmtPrintln(integerlt=4)

fallthrough

default

fmtPrintln(defaultcase)

Thisprogramprintsthefollowinginformation

integerlt=6

integerlt=7

integerlt=8

defaultcase

FunctionsUsethefunckeywordtodefineafunction

funcfuncName(input1type1input2type2)(output1type1output2type2)

functionbody

multi-valuereturn

returnvalue1value2

Wecanextrapolatethefollowinginformationfromtheexampleabove

UsekeywordfunctodefineafunctionfuncNameFunctionshavezerooneormorethanoneargumentsTheargumenttypecomesaftertheargumentnameandargumentsareseparatedbyFunctionscanreturnmultiplevaluesTherearetworeturnvaluesnamedoutput1andoutput2youcanomittheirnamesandusetheirtypeonlyIfthereisonlyonereturnvalueandyouomittedthenameyoudontneedbracketsforthereturnvaluesIfthefunctiondoesnthavereturnvaluesyoucanomitthereturnparametersaltogetherIfthefunctionhasreturnvaluesyouhavetousethereturnstatementsomewhereinthebodyofthefunction

Letsseeonepracticalexample(calculatemaximumvalue)

packagemain

importfmt

returngreatervaluebetweenaandb

funcmax(abint)int

ifagtb

returna

returnb

funcmain()

max_xy=max(xy)callfunctionmax(xy)

max_xz=max(xz)callfunctionmax(xz)

fmtPrintf(max(dd)=dnxymax_xy)

fmtPrintf(max(dd)=dnxzmax_xz)

fmtPrintf(max(dd)=dnyzmax(yz))callfunctionhere

IntheaboveexampletherearetwoargumentsinthefunctionmaxtheirtypesarebothintsothefirsttypecanbeomittedForinstanceabintinsteadofaintbintThesamerulesapplyforadditionalargumentsNoticeherethatmaxonlyhasonereturnvaluesoweonlyneedtowritethetypeofitsreturnvalue-thisistheshortformofwritingit

Multi-valuereturn

OnethingthatGoisbetteratthanCisthatitsupportsmulti-valuereturns

Wellusethefollowingexamplehere

packagemain

importfmt

returnresultsofA+BandAB

funcSumAndProduct(ABint)(intint)

returnA+BAB

funcmain()

xPLUSyxTIMESy=SumAndProduct(xy)

fmtPrintf(d+d=dnxyxPLUSy)

fmtPrintf(dd=dnxyxTIMESy)

Theaboveexamplereturnstwovalueswithoutnames-youhavetheoptionofnamingthemalsoIfwenamedthereturnvalueswewouldjustneedtousereturntoreturnthevaluessincetheyareinitializedinthefunctionautomaticallyNoticethatifyourfunctionsaregoingtobeusedoutsideofthepackagewhichmeansyourfunctionnamesstartwithacapitalletteryoudbetterwritecompletestatementsforreturnitmakesyourcodemorereadable

funcSumAndProduct(ABint)(addintmultipliedint)

add=A+B

multiplied=AB

return

Variadicfunctions

GosupportsfunctionswithavariablenumberofargumentsThesefunctionsarecalledvariadicwhichmeansthefunctionallowsanuncertainnumbersofarguments

funcmyfunc(argint)

arghellipinttellsGothatthisisafunctionthathasvariableargumentsNoticethattheseargumentsaretypeintInthebodyoffunctiontheargbecomesasliceofint

for_n=rangearg

fmtPrintf(Andthenumberisdnn)

Passbyvalueandpointers

Whenwepassanargumenttothefunctionthatwascalledthatfunctionactuallygetsthecopyofourvariablessoanychangewillnotaffecttotheoriginalvariable

Letsseeoneexampleinordertoprovewhatimsaying

packagemain

importfmt

simplefunctiontoadd1toa

funcadd1(aint)int

a=a+1wechangevalueofa

returnareturnnewvalueofa

funcmain()

fmtPrintln(x=x)shouldprintx=3

x1=add1(x)calladd1(x)

fmtPrintln(x+1=x1)shouldprintx+1=4

CanyouseethatEventhoughwecalledadd1withxtheoriginvalueofxdoesntchange

Thereasonisverysimplewhenwecalledadd1wegaveacopyofxtoitnotthexitself

NowyoumayaskhowIcanpasstherealxtothefunction

WeneedusepointershereWeknowvariablesarestoredinmemoryandtheyhavesomememoryaddressesSoifwewanttochangethevalueofavariablewemustchangeitsmemoryaddressThereforethefunctionadd1hastoknowthememoryaddressofxinordertochangeitsvalueHerewepassampxtothefunctionandchangetheargumentstypetothepointertypeintBeawarethatwepassacopyofthepointernotcopyofvalue

packagemain

importfmt

funcadd1(aint)int

a=a+1wechangedvalueofa

funcmain()

x1=add1(ampx)calladd1(ampx)passmemoryaddressofx

NowwecanchangethevalueofxinthefunctionsWhydoweusepointersWhataretheadvantages

AllowsustousemorefunctionstooperateononevariableLowcostbypassingmemoryaddresses(8bytes)copyisnotanefficientwaybothintermsoftimeandspacetopassvariableschannelsliceandmaparereferencetypessotheyusepointerswhenpassingtofunctionsbydefault(AttentionIfyouneedtochangethelengthofsliceyouhavetopasspointersexplicitly)

deferGohasawelldesignedkeywordcalleddeferYoucanhavemanydeferstatementsinonefunctiontheywillexecuteinreverseorderwhentheprogramexecutestotheendoffunctionsInthecasewheretheprogramopenssomeresourcefilesthesefileswouldhavetobeclosedbeforethefunctioncanreturnwitherrorsLetsseesomeexamples

funcReadWrite()bool

fileOpen(file)

Dosomework

iffailureX

fileClose()

returnfalse

iffailureY

fileClose()

returnfalse

fileClose()

returntrue

WesawsomecodebeingrepeatedseveraltimesdefersolvesthisproblemverywellItdoesntonlyhelpyoutowritecleancodebutalsomakesyourcodemorereadable

funcReadWrite()bool

fileOpen(file)

deferfileClose()

iffailureX

returnfalse

iffailureY

returnfalse

returntrue

IftherearemorethanonedeferstheywillexecutebyreverseorderThefollowingexamplewillprint43210

fori=0ilt5i++

deferfmtPrintf(di)

Functionsasvaluesandtypes

FunctionsarealsovariablesinGowecanusetypetodefinethemFunctionsthathavethesamesignaturecanbeseenasthesametype

typetypeNamefunc(input1inputType1input2inputType2[])(result1resultType1[])

WhatstheadvantageofthisfeatureTheansweristhatitallowsustopassfunctionsasvalues

packagemain

importfmt

typetestIntfunc(int)booldefineafunctiontypeofvariable

funcisOdd(integerint)bool

returninteger2=0

funcisEven(integerint)bool

returninteger2==0

passthefunction`f`asanargumenttoanotherfunction

funcfilter(slice[]intftestInt)[]int

varresult[]int

for_value=rangeslice

iff(value)

result=append(resultvalue)

returnresult

varslice=[]int123457

funcmain()

odd=filter(sliceisOdd)

even=filter(sliceisEven)

fmtPrintln(slice=slice)

fmtPrintln(Oddelementsofsliceareodd)

fmtPrintln(Evenelementsofsliceareeven)

ItsveryusefulwhenweuseinterfacesAsyoucanseetestIntisavariablethathasafunctionastypeandthereturnedvaluesandargumentsoffilterarethesameasthoseoftestIntThereforewecanhavecomplexlogicinourprogramswhilemaintainingflexibilityinourcode

PanicandRecover

Godoesnthavetry-catchstructurelikeJavadoesInsteadofthrowingexceptionsGousespanicandrecovertodealwitherrorsHoweveryoushouldntusepanicverymuchalthoughitspowerful

Panicisabuilt-infunctiontobreakthenormalflowofprogramsandgetintopanicstatusWhenafunctionFcallspanicFwillnotcontinueexecutingbutitsdeferfunctionswillcontinuetoexecuteThenFgoesbacktothebreakpointwhichcausedthepanicstatusTheprogramwillnotterminateuntilallofthesefunctionsreturnwithpanictothefirstlevelofthatgoroutinepaniccanbeproducedbycallingpanicintheprogramandsomeerrorsalsocausepaniclikearrayaccessoutofboundserrors

Recoverisabuilt-infunctiontorecovergoroutinesfrompanicstatusCallingrecoverindeferfunctionsisusefulbecausenormalfunctionswillnotbeexecutedwhentheprogramisinthepanicstatusItcatchespanicvaluesiftheprogramisinthepanicstatusanditgetsniliftheprogramisnotinpanicstatus

Thefollowingexampleshowshowtousepanic

varuser=osGetenv(USER)

funcinit()

ifuser==

panic(novaluefor$USER)

Thefollowingexampleshowshowtocheckpanic

functhrowsPanic(ffunc())(bbool)

deferfunc()

ifx=recover()x=nil

b=true

f()iffcausespanicitwillrecover

return

mainfunctionandinitfunction

GohastworetentionswhicharecalledmainandinitwhereinitcanbeusedinallpackagesandmaincanonlybeusedinthemainpackageThesetwofunctionsarenotabletohaveargumentsorreturnvaluesEventhoughwecanwritemanyinitfunctionsinonepackageIstronglyrecommendwritingonlyoneinitfunctionforeachpackage

Goprogramswillcallinit()andmain()automaticallysoyoudontneedtocallthembyyourselfForeverypackagetheinitfunctionisoptionalbutpackagemainhasoneandonlyonemainfunction

ProgramsinitializeandbeginexecutionfromthemainpackageIfthemainpackageimportsotherpackagestheywillbeimportedinthecompiletimeIfonepackageisimportedmanytimesitwillbeonlycompiledonceAfterimportingpackagesprogramswillinitializetheconstantsandvariableswithintheimportedpackagesthenexecutetheinitfunctionifitexistsandsoonAfteralltheotherpackagesareinitializedprogramswillinitializeconstantsandvariablesinthemainpackagethenexecutetheinitfunctioninsidethepackageifitexistsThefollowingfigureshowstheprocess

Figure26FlowofprogramsinitializationinGo

import

WeuseimportveryofteninGoprogramsasfollows

import(

Thenweusefunctionsinthatpackageasfollows

fmtPrintln(helloworld)

fmtisfromGostandardlibraryitislocatedwithin$GOROOTpkgGosupportsthird-partypackagesintwoways

1 RelativepathimportmodelloadpackageinthesamedirectoryIdontrecommendthisway2 Absolutepathimportshorturlmodelloadpackageinpath$GOPATHpkgshorturlmodel

Therearesomespecialoperatorswhenweimportpackagesandbeginnersarealwaysconfusedbytheseoperators

1 DotoperatorSometimeweseepeopleusefollowingwaytoimportpackages

import(

ThedotoperatormeansyoucanomitthepackagenamewhenyoucallfunctionsinsideofthatpackageNowfmtPrintf(Helloworld)becomestoPrintf(Helloworld)

2 AliasoperationItchangesthenameofthepackagethatweimportedwhenwecallfunctionsthatbelongtothatpackage

import(

NowfmtPrintf(Helloworld)becomestofPrintf(Helloworld)3 _operatorThisistheoperatorthatisdifficulttounderstandwithoutsomeoneexplainingittoyou

import(

databasesql

_githubcomziutekmymysqlgodrv

The_operatoractuallymeanswejustwanttoimportthatpackageandexecuteitsinitfunctionandwearenotsureifwewanttousethefunctionsbelongingtothatpackage

LinksDirectoryPrevioussectionGofoundationNextsectionstruct

24struct

structWecandefinenewtypesofcontainersofotherpropertiesorfieldsinGojustlikeinotherprogramminglanguagesForexamplewecancreateatypecalledpersontorepresentapersonwithfieldsnameandageWecallthiskindoftypeastruct

typepersonstruct

namestring

ageint

Lookhoweasyitistodefineastruct

Therearetwofields

nameisastringusedtostoreapersonsnameageisaintusedtostoreapersonsage

Letsseehowtouseit

typepersonstruct

namestring

ageint

varPpersonpispersontype

Pname=AstaxieassignAstaxietothefieldnameofp

Page=25assign25tofieldageofp

fmtPrintf(ThepersonsnameissnPname)accessfieldnameofp

Therearethreemorewaystoinitializeastruct

Assigninitialvaluesbyorder

P=personTom25

Usetheformatfieldvaluetoinitializethestructwithoutorder

P=personage24nameBob

Defineananonymousstructtheninitializeit

P=structnamestringageintAmy18

Letsseeacompleteexample

struct

packagemain

importfmt

defineanewtype

typepersonstruct

namestring

ageint

structispassedbyvalue

comparetheageoftwopeoplethenreturntheolderpersonanddifferencesofage

funcOlder(p1p2person)(personint)

ifp1agegtp2age

returnp1p1age-p2age

returnp2p2age-p1age

funcmain()

vartomperson

tomnametomage=Tom18

bob=personage25nameBob

paul=personPaul43

tb_Oldertb_diff=Older(tombob)

tp_Oldertp_diff=Older(tompaul)

bp_Olderbp_diff=Older(bobpaul)

fmtPrintf(Ofsandssisolderbydyearsntomnamebobnametb_Oldernametb_diff)

fmtPrintf(Ofsandssisolderbydyearsntomnamepaulnametp_Oldernametp_diff)

fmtPrintf(Ofsandssisolderbydyearsnbobnamepaulnamebp_Oldernamebp_diff)

embeddedfieldsinstructIvejustintroducedtoyouhowtodefineastructwithfieldnamesandtypeInfactGosupportsfieldswithoutnamesbutwithtypesWecalltheseembeddedfields

Whentheembeddedfieldisastructallthefieldsinthatstructwillimplicitlybethefieldsinthestructinwhichithasbeenembedded

Letsseeoneexample

struct

packagemain

importfmt

typeHumanstruct

namestring

ageint

weightint

typeStudentstruct

HumanembeddedfielditmeansStudentstructincludesallfieldsthatHumanhas

specialtystring

funcmain()

instantiateandinitializeastudent

mark=StudentHumanMark25120ComputerScience

accessfields

fmtPrintln(Hisnameismarkname)

fmtPrintln(Hisageismarkage)

fmtPrintln(Hisweightismarkweight)

fmtPrintln(Hisspecialtyismarkspecialty)

modifymarksspecialty

markspecialty=AI

fmtPrintln(Markchangedhisspecialty)

fmtPrintln(MarkbecomeoldHeisnotanathleteanymore)

markage=46

markweight+=60

Figure27EmbeddinginStudentandHuman

WeseethatwecanaccesstheageandnamefieldsinStudentjustlikewecaninHumanThisishowembeddedfieldsworkItsverycoolisntitHoldontheressomethingcoolerYoucanevenuseStudenttoaccessHumaninthisembeddedfield

markHuman=HumanMarcus55220

markHumanage-=1

AllthetypesinGocanbeusedasembeddedfields

struct

packagemain

importfmt

typeSkills[]string

typeHumanstruct

namestring

ageint

weightint

typeStudentstruct

Humanstructasembeddedfield

Skillsstringsliceasembeddedfield

intbuilt-intypeasembeddedfield

specialtystring

funcmain()

initializeStudentJane

jane=StudentHumanHumanJane35100specialtyBiology

accessfields

fmtPrintln(Hernameisjanename)

fmtPrintln(Herageisjaneage)

fmtPrintln(Herweightisjaneweight)

fmtPrintln(Herspecialtyisjanespecialty)

modifyvalueofskillfield

janeSkills=[]stringanatomy

fmtPrintln(HerskillsarejaneSkills)

fmtPrintln(Sheacquiredtwonewones)

janeSkills=append(janeSkillsphysicsgolang)

fmtPrintln(HerskillsnowarejaneSkills)

modifyembeddedfield

janeint=3

fmtPrintln(Herpreferrednumberisjaneint)

Intheaboveexamplewecanseethatalltypescanbeembeddedfieldsandwecanusefunctionstooperateonthem

ThereisonemoreproblemhoweverIfHumanhasafieldcalledphoneandStudenthasafieldwithsamenamewhatshouldwedo

GouseaverysimplewaytosolveitTheouterfieldsgetupperaccesslevelswhichmeanswhenyouaccessstudentphonewewillgetthefieldcalledphoneinstudentnottheoneintheHumanstructThisfeaturecanbesimplyseenasfieldoverloading

struct

packagemain

importfmt

typeHumanstruct

namestring

ageint

phonestringHumanhasphonefield

typeEmployeestruct

specialtystring

phonestringphoneinemployee

funcmain()

Bob=EmployeeHumanBob34777-444-XXXXDesigner333-222

fmtPrintln(BobsworkphoneisBobphone)

fmtPrintln(BobspersonalphoneisBobHumanphone)

LinksDirectoryPrevioussectionControlstatementsandfunctionsNextsectionObject-oriented

struct

Object-orientedWetalkedaboutfunctionsandstructsinthelasttwosectionsbutdidyoueverconsiderusingfunctionsasfieldsofastructInthissectionIwillintroduceyoutoanotherformoffunctionthathasareceiverwhichiscalledamethod

methodSupposeyoudefinearectanglestructandyouwanttocalculateitsareaWedtypicallyusethefollowingcodetoachievethisgoal

packagemain

importfmt

typeRectanglestruct

widthheightfloat64

funcarea(rRectangle)float64

returnrwidthrheight

funcmain()

r1=Rectangle122

r2=Rectangle94

fmtPrintln(Areaofr1isarea(r1))

TheaboveexamplecancalculatearectanglesareaWeusethefunctioncalledareabutitsnotamethodoftherectanglestruct(likeclassmethodsinclassicobject-orientedlanguages)Thefunctionandstructaretwoindependentthingsasyoumaynotice

ItsnotaproblemsofarHoweverifyoualsohavetocalculatetheareaofacirclesquarepentagonoranyotherkindofshapeyouaregoingtoneedtoaddadditionalfunctionswithverysimilarnames

Figure28Relationshipbetweenfunctionandstruct

ObviouslythatsnotcoolAlsotheareashouldreallybethepropertyofacircleorrectangle

ThisiswhereamethodcomestoplayThemethodisafunctionaffiliatedwithatypeIthassimilarsyntaxasfunctionexceptafterthefunckeywordhasaparametercalledthereceiverwhichisthemainbodyofthatmethod

UsingthesameexampleRectangleArea()belongsdirectlytorectangleinsteadofasaperipheralfunctionMorespecificallylengthwidthandArea()allbelongtorectangle

AsRobPikesaid

Amethodisafunctionwithanimplicitfirstargumentcalledareceiver

Syntaxofmethod

func(rReceiverType)funcName(parameters)(results)

Letschangeourexampleusingmethodinstead

Object-oriented

packagemain

import(

typeCirclestruct

radiusfloat64

typeRectanglestruct

widthheightfloat64

method

func(cCircle)Area()float64

returncradiuscradiusmathPi

method

func(rRectangle)Area()float64

returnrwidthrheight

funcmain()

c1=Circle10

c2=Circle25

r1=Rectangle94

r2=Rectangle122

fmtPrintln(Areaofc1isc1Area())

fmtPrintln(Areaofr1isr1Area())

Notesforusingmethods

IfthenameofmethodsarethesamebuttheydontsharethesamereceiverstheyarenotthesameMethodsareabletoaccessfieldswithinreceiversUsetocallamethodinthestructthesamewayfieldsarecalled

Figure29Methodsaredifferentindifferentstructs

IntheexampleabovetheArea()methodsbelongtobothRectangleandCirclerespectivelysothereceiversareRectangleandCircle

OnethingthatsworthnotingisthatthemethodwithadottedlinemeansthereceiverispassedbyvaluenotbyreferenceThedifferencebetweenthemisthatamethodcanchangeitsreceiversvalueswhenthereceiverispassedbyreferenceanditgetsacopyofthereceiverwhenthereceiverispassedbyvalue

CanthereceiveronlybeastructOfcoursenotAnytypecanbethereceiverofamethodYoumaybeconfusedaboutcustomizedtypesStructisaspecialkindofcustomizedtype-therearemorecustomizedtypes

Usethefollowingformattodefineacustomizedtype

typetypeNametypeLiteral

Examplesofcustomizedtypes

Object-oriented

typeageint

typemoneyfloat32

typemonthsmap[string]int

m=months

January31

February28

December31

IhopethatyouknowhowtousecustomizedtypesnowSimilartotypedefinCweuseagestosubstituteintintheaboveexample

Letsgetbacktotalkingaboutmethod

Youcanuseasmanymethodsincustomtypesasyouwant

packagemain

importfmt

const(

WHITE=iota

YELLOW

typeBoxstruct

widthheightdepthfloat64

colorColor

typeColorbyte

typeBoxList[]Boxasliceofboxes

method

func(bBox)Volume()float64

returnbwidthbheightbdepth

methodwithapointerreceiver

func(bBox)SetColor(cColor)

bcolor=c

method

func(blBoxList)BiggestsColor()Color

k=Color(WHITE)

for_b=rangebl

ifbVolume()gtv

v=bVolume()

k=bcolor

returnk

method

func(blBoxList)PaintItBlack()

fori_=rangebl

bl[i]SetColor(BLACK)

method

func(cColor)String()string

Object-oriented

strings=[]stringWHITEBLACKBLUEREDYELLOW

returnstrings[c]

funcmain()

boxes=BoxList

Box444RED

Box10101YELLOW

Box1120BLACK

Box10101BLUE

Box10301WHITE

Box202020YELLOW

fmtPrintf(Wehavedboxesinoursetnlen(boxes))

fmtPrintln(Thevolumeofthefirstoneisboxes[0]Volume()cmsup3)

fmtPrintln(Thecolorofthelastoneisboxes[len(boxes)-1]colorString())

fmtPrintln(ThebiggestoneisboxesBiggestsColor()String())

Letspaintthemallblack

boxesPaintItBlack()

fmtPrintln(Thecolorofthesecondoneisboxes[1]colorString())

fmtPrintln(ObviouslynowthebiggestoneisboxesBiggestsColor()String())

Wedefinesomeconstantsandcustomizedtypes

UseColorasaliasofbyteDefineastructBoxwhichhasfieldsheightwidthlengthandcolorDefineastructBoxListwhichhasBoxasitsfield

Thenwedefinedsomemethodsforourcustomizedtypes

Volume()usesBoxasitsreceiverandreturnsthevolumeofBoxSetColor(cColor)changesBoxscolorBiggestsColor()returnsthecolorwhichhasthebiggestvolumePaintItBlack()setscolorforallBoxinBoxListtoblackString()useColorasitsreceiverreturnsthestringformatofcolorname

IsitmuchclearerwhenweusewordstodescribeourrequirementsWeoftenwriteourrequirementsbeforewestartcoding

Usepointerasreceiver

LetstakealookatSetColormethodItsreceiverisapointerofBoxYesyoucanuseBoxasareceiverWhydoweuseapointerhereBecausewewanttochangeBoxscolorinthismethodThusifwedontuseapointeritwillonlychangethevalueinsideacopyofBox

Ifweseethatareceiveristhefirstargumentofamethoditsnothardtounderstandhowitworks

Youmightbeaskingwhywearentusing(b)Color=cinsteadofbColor=cintheSetColor()methodEitheroneisOKherebecauseGoknowshowtointerprettheassignmentDoyouthinkGoismorefascinatingnow

Youmayalsobeaskingwhetherweshoulduse(ampbl[i])SetColor(BLACK)inPaintItBlackbecausewepassapointertoSetColorAgaineitheroneisOKbecauseGoknowshowtointerpretit

Inheritanceofmethod

WelearnedaboutinheritanceoffieldsinthelastsectionSimilarlywealsohavemethodinheritanceinGoIfananonymousfieldhasmethodsthenthestructthatcontainsthefieldwillhaveallthemethodsfromitaswell

Object-oriented

packagemain

importfmt

typeHumanstruct

namestring

ageint

phonestring

typeStudentstruct

Humananonymousfield

schoolstring

typeEmployeestruct

companystring

defineamethodinHuman

func(hHuman)SayHi()

fmtPrintf(HiIamsyoucancallmeonsnhnamehphone)

funcmain()

sam=EmployeeHumanSam45111-888-XXXXGolangInc

mark=StudentHumanMark25222-222-YYYYMIT

samSayHi()

markSayHi()

MethodOverridingIfwewantEmployeetohaveitsownmethodSayHiwecandefineamethodthathasthesamenameinEmployeeanditwillhideSayHiinHumanwhenwecallit

Object-oriented

packagemain

importfmt

typeHumanstruct

namestring

ageint

phonestring

typeStudentstruct

schoolstring

typeEmployeestruct

companystring

func(hHuman)SayHi()

func(eEmployee)SayHi()

fmtPrintf(HiIamsIworkatsCallmeonsnename

ecompanyephone)Yesyoucansplitinto2lineshere

funcmain()

samSayHi()

markSayHi()

YouareabletowriteanObject-orientedprogramnowandmethodsuseruleofcapitallettertodecidewhetherpublicorprivateaswell

LinksDirectoryPrevioussectionstructNextsectioninterface

Object-oriented

26Interface

InterfaceOneofthesubtlestdesignfeaturesinGoareinterfacesAfterreadingthissectionyouwilllikelybeimpressedbytheirimplementation

Whatisaninterface

Inshortaninterfaceisasetofmethodsthatweusetodefineasetofactions

LiketheexamplesinprevioussectionsbothStudentandEmployeecanSayHi()buttheydontdothesamething

LetsdosomemoreworkWelladdonemoremethodSing()tothemalongwiththeBorrowMoney()methodtoStudentandtheSpendSalary()methodtoEmployee

NowStudenthasthreemethodscalledSayHi()Sing()andBorrowMoney()andEmployeehasSayHi()Sing()andSpendSalary()

ThiscombinationofmethodsiscalledaninterfaceandisimplementedbybothStudentandEmployeeSoStudentandEmployeeimplementtheinterfaceSayHi()andSing()AtthesametimeEmployeedoesntimplementtheinterfaceBorrowMoney()andStudentdoesntimplementtheinterfaceSpendSalary()ThisisbecauseEmployeedoesnthavethemethodBorrowMoney()andStudentdoesnthavethemethodSpendSalary()

TypeofInterfaceAninterfacedefinesasetofmethodssoifatypeimplementsallthemethodswesaythatitimplementstheinterface

interface

typeHumanstruct

namestring

ageint

phonestring

typeStudentstruct

schoolstring

loanfloat32

typeEmployeestruct

companystring

moneyfloat32

defineinterfaces

typeMeninterface

SayHi()

Sing(lyricsstring)

Guzzle(beerSteinstring)

typeYoungChapinterface

SayHi()

Sing(songstring)

BorrowMoney(amountfloat32)

typeElderlyGentinterface

SayHi()

Sing(songstring)

SpendSalary(amountfloat32)

func(hHuman)SayHi()

func(hHuman)Sing(lyricsstring)

fmtPrintln(Lalalalalalalalalalalyrics)

func(hHuman)Guzzle(beerSteinstring)

fmtPrintln(GuzzleGuzzleGuzzlebeerStein)

EmployeeoverloadsSayHi

func(sStudent)BorrowMoney(amountfloat32)

sloan+=amount(againandagainand)

func(eEmployee)SpendSalary(amountfloat32)

emoney-=amountMorevodkapleaseGetmethroughtheday

Weknowthataninterfacecanbeimplementedbyanytypeandonetypecanimplementmanyinterfacessimultaneously

Notethatanytypeimplementstheemptyinterfaceinterfacebecauseitdoesnthaveanymethodsandalltypeshavezeromethodsbydefault

Valueofinterface

interface

SowhatkindofvaluescanbeputintheinterfaceIfwedefineavariableasatypeinterfaceanytypethatimplementstheinterfacecanassignedtothisvariable

LiketheaboveexampleifwedefineavariablemasinterfaceMenthenanyoneofStudentHumanorEmployeecanbeassignedtomSowecouldhaveasliceofMenandanytypethatimplementsinterfaceMencanassigntothissliceBeawarehoweverthatthesliceofinterfacedoesnthavethesamebehaviorasasliceofothertypes

packagemain

importfmt

typeHumanstruct

namestring

ageint

phonestring

typeStudentstruct

schoolstring

loanfloat32

typeEmployeestruct

companystring

moneyfloat32

InterfaceMenimplementedbyHumanStudentandEmployee

typeMeninterface

SayHi()

Sing(lyricsstring)

method

func(hHuman)SayHi()

method

fmtPrintln(Lalalalalyrics)

method

funcmain()

mike=StudentHumanMike25222-222-XXXMIT000

paul=StudentHumanPaul26111-222-XXXHarvard100

sam=EmployeeHumanSam36444-222-XXXGolangInc1000

tom=EmployeeHumanSam36444-222-XXXThingsLtd5000

defineinterfacei

variMen

icanstoreStudent

i=mike

fmtPrintln(ThisisMikeaStudent)

iSayHi()

iSing(Novemberrain)

icanstoreEmployee

fmtPrintln(ThisisTomanEmployee)

iSayHi()

interface

iSing(Borntobewild)

sliceofMen

fmtPrintln(LetsuseasliceofMenandseewhathappens)

x=make([]Men3)

thesethreeelementsaredifferenttypesbuttheyallimplementedinterfaceMen

x[0]x[1]x[2]=paulsammike

for_value=rangex

valueSayHi()

Aninterfaceisasetofabstractmethodsandcanbeimplementedbynon-interfacetypesItcannotthereforeimplementitself

Emptyinterface

AnemptyinterfaceisaninterfacethatdoesntcontainanymethodssoalltypesimplementanemptyinterfaceThisfactisveryusefulwhenwewanttostorealltypesatsomepointandissimilartovoidinC

defineaasemptyinterface

varvoidinterface

s=Helloworld

acanstorevalueofanytype

void=i

void=s

Ifafunctionusesanemptyinterfaceasitsargumenttypeitcanacceptanytypeifafunctionusesemptyinterfaceasitsreturnvaluetypeitcanreturnanytype

Methodargumentsofaninterface

AnyvariablecanbeusedinaninterfaceSohowcanweusethisfeaturetopassanytypeofvariabletoafunction

ForexampleweusefmtPrintlnalotbuthaveyouevernoticedthatitcanacceptanytypeofargumentLookingattheopensourcecodeoffmtweseethefollowingdefinition

typeStringerinterface

String()string

ThismeansanytypethatimplementsinterfaceStringercanbepassedtofmtPrintlnasanargumentLetsproveit

interface

packagemain

import(

strconv

typeHumanstruct

namestring

ageint

phonestring

HumanimplementsfmtStringer

func(hHuman)String()string

returnName+hname+Age+strconvItoa(hage)+yearsContact+hphone

funcmain()

Bob=HumanBob39000-7777-XXX

fmtPrintln(ThisHumanisBob)

LookingbacktotheexampleofBoxyouwillfindthatColorimplementsinterfaceStringeraswellsoweareabletocustomizetheprintformatIfwedontimplementthisinterfacefmtPrintlnprintsthetypewithitsdefaultformat

fmtPrintln(ThebiggestoneisboxesBiggestsColor())

AttentionIfthetypeimplementedtheinterfaceerrorfmtwillcallError()soyoudonthavetoimplementStringeratthispoint

TypeofvariableinaninterfaceIfavariableisthetypethatimplementsaninterfaceweknowthatanyothertypethatimplementsthesameinterfacecanbeassignedtothisvariableThequestionishowcanweknowthespecifictypestoredintheinterfaceTherearetwowayswhichIwillshowyou

AssertionofComma-okpattern

Gohasthesyntaxvalueok=element(T)ThischeckstoseeifthevariableisthetypethatweexpectwherevalueisthevalueofthevariableokisavariableofbooleantypeelementistheinterfacevariableandtheTisthetypeofassertion

Iftheelementisthetypethatweexpectokwillbetruefalseotherwise

Letsuseanexampletoseemoreclearly

interface

packagemain

import(

strconv

typeElementinterface

typeList[]Element

typePersonstruct

namestring

ageint

func(pPerson)String()string

return(name+pname+-age+strconvItoa(page)+years)

funcmain()

list=make(List3)

list[0]=1anint

list[1]=Helloastring

list[2]=PersonDennis70

forindexelement=rangelist

ifvalueok=element(int)ok

fmtPrintf(list[d]isanintanditsvalueisdnindexvalue)

elseifvalueok=element(string)ok

fmtPrintf(list[d]isastringanditsvalueissnindexvalue)

elseifvalueok=element(Person)ok

fmtPrintf(list[d]isaPersonanditsvalueissnindexvalue)

fmtPrintf(list[d]isofadifferenttypenindex)

Itsquiteeasytousethispatternbutifwehavemanytypestotestwedbetteruseswitch

switchtest

Letsuseswitchtorewritetheaboveexample

interface

packagemain

import(

strconv

typeList[]Element

typePersonstruct

namestring

ageint

funcmain()

list=make(List3)

list[0]=1anint

switchvalue=element(type)

caseint

casestring

casePerson

default

fmtPrintln(list[d]isofadifferenttypeindex)

Onethingyoushouldrememberisthatelement(type)cannotbeusedoutsideoftheswitchbodywhichmeansinthatcaseyouhavetousethecomma-okpattern

Embeddedinterfaces

ThemostbeautifulthingisthatGohasalotofbuilt-inlogicsyntaxsuchasanonymousfieldsinstructNotsuprisinglywecanuseinterfacesasanonymousfieldsaswellbutwecallthemEmbeddedinterfacesHerewefollowthesamerulesasanonymousfieldsMorespecificallyifaninterfacehasanotherinterfaceembeddedwithinititwillbehaveasifithasallthemethodsthattheembeddedinterfacehas

Wecanseethatthesourcefileincontainerheaphasthefollowingdefinition

typeInterfaceinterface

sortInterfaceembeddedsortInterface

Push(xinterface)aPushmethodtopushelementsintotheheap

Pop()interfaceaPopmethodthatpopselementsfromtheheap

WeseethatsortInterfaceisanembeddedinterfacesotheaboveInterfacehasthethreemethodscontainedwithinthesortInterfaceimplicitly

interface

Lenisthenumberofelementsinthecollection

Len()int

Lessreturnswhethertheelementwithindexishouldsort

beforetheelementwithindexj

Less(ijint)bool

Swapswapstheelementswithindexesiandj

Swap(ijint)

AnotherexampleistheioReadWriterinpackageio

ioReadWriter

typeReadWriterinterface

Reader

Writer

Reflection

ReflectioninGoisusedfordetermininginformationatruntimeWeusethereflectpackageandTheLawsofReflectionpostexplainshowreflectworksinGo

TherearethreestepsinvolvedwhenusingreflectFirstweneedtoconvertaninterfacetoreflecttypes(reflectTypeorreflectValuethisdependsonthesituation)

t=reflectTypeOf(i)getmeta-dataintypeiandusettogetallelements

v=reflectValueOf(i)getactualvalueintypeiandusevtochangeitsvalue

Afterthatwecanconvertthereflectedtypestogetthevaluesthatweneed

varxfloat64=34

t=reflectTypeOf(x)

v=reflectValueOf(x)

fmtPrintln(typet)

fmtPrintln(valuev)

fmtPrintln(kindisfloat64vKind()==reflectFloat64)

FinallyifwewanttochangethevaluesofthereflectedtypesweneedtomakeitmodifiableAsdiscussedearlierthereisadifferencebetweenpassbyvalueandpassbyreferenceThefollowingcodewillnotcompile

varxfloat64=34

v=reflectValueOf(x)

vSetFloat(71)

Insteadwemustusethefollowingcodetochangethevaluesfromreflecttypes

varxfloat64=34

p=reflectValueOf(ampx)

v=pElem()

vSetFloat(71)

Wehavejustdiscussedthebasicsofreflectionhoweveryoumustpracticemoreinordertounderstandmore

interface

DirectoryPrevioussectionObject-orientedNextsectionConcurrency

interface

ConcurrencyItissaidthatGoistheCofthe21stcenturyIthinktherearetworeasonsforitFirstGoisasimplelanguageSecondconcurrencyisahottopicintodaysworldandGosupportsthisfeatureatthelanguagelevel

goroutinegoroutinesandconcurrencyarebuiltintothecoredesignofGoTheyresimilartothreadsbutworkdifferentlyGoalsogivesyoufullsupporttosharingmemoryinyourgoroutinesOnegoroutineusuallyuses4~5KBofstackmemoryThereforeitsnothardtorunthousandsofgoroutinesonasinglecomputerAgoroutineismorelightweightmoreefficientandmoreconvenientthansystemthreads

goroutinesrunonthethreadmanageratruntimeinGoWeusethegokeywordtocreateanewgoroutinewhichisafunctionattheunderlyinglevel(main()isagoroutine)

gohello(abc)

Letsseeanexample

packagemain

import(

runtime

funcsay(sstring)

fori=0ilt5i++

runtimeGosched()

fmtPrintln(s)

funcmain()

gosay(world)createanewgoroutine

say(hello)currentgoroutine

Output

WeseethatitsveryeasytouseconcurrencyinGobyusingthekeywordgoIntheaboveexamplethesetwogoroutinessharesomememorybutwewouldbetterofffollowingthedesignrecipeDontuseshareddatatocommunicateusecommunicationtosharedata

runtimeGosched()meanslettheCPUexecuteothergoroutinesandcomebackatsomepoint

InGo15theruntimenowsetsthedefaultnumberofthreadstorunsimultaneouslydefinedbyGOMAXPROCStothenumberofcoresavailableontheCPU

Concurrency

BeforeGo15ThescheduleronlyusesonethreadtorunallgoroutineswhichmeansitonlyimplementsconcurrencyIfyouwanttousemoreCPUcoresinordertotakeadvantageofparallelprocessingyouhavetocallruntimeGOMAXPROCS(n)tosetthenumberofcoresyouwanttouseIfnlt1itchangesnothing

channelsgoroutinesruninthesamememoryaddressspacesoyouhavetomaintainsynchronizationwhenyouwanttoaccesssharedmemoryHowdoyoucommunicatebetweendifferentgoroutinesGousesaverygoodcommunicationmechanismcalledchannelAchannelisliketwo-waypipelineinUnixshellsusechanneltosendorreceivedataTheonlydatatypethatcanbeusedinchannelsisthetypechannelandthekeywordchanBeawarethatyouhavetousemaketocreateanewchannel

ci=make(chanint)

cs=make(chanstring)

cf=make(chaninterface)

channelusestheoperatorlt-tosendorreceivedata

chlt-vsendvtochannelch

v=lt-chreceivedatafromchandassigntov

Letsseemoreexamples

packagemain

importfmt

funcsum(a[]intcchanint)

total=0

for_v=rangea

total+=v

clt-totalsendtotaltoc

funcmain()

a=[]int728-940

c=make(chanint)

gosum(a[len(a)2]c)

xy=lt-clt-creceivefromc

fmtPrintln(xyx+y)

SendingandreceivingdatainchannelsblocksbydefaultsoitsmucheasiertousesynchronousgoroutinesWhatImeanbyblockisthatagoroutinewillnotcontinuewhenreceivingdatafromanemptychannelie(value=lt-ch)untilothergoroutinessenddatatothischannelOntheotherhandthegoroutinewillnotcontinueuntilthedataitsendstoachannelie(chlt-5)isreceived

BufferedchannelsIintroducednon-bufferedchannelsaboveGoalsohasbufferedchannelsthatcanstoremorethanasingleelementForexamplech=make(chanbool4)herewecreateachannelthatcanstore4booleanelementsSointhischannelweareabletosend4elementsintoitwithoutblockingbutthegoroutinewillbeblockedwhenyoutrytosendafifthelementandnogoroutinereceivesit

Concurrency

ch=make(chantypen)

n==0non-buffer（block）

ngt0buffer（non-blockuntilnelementsinthechannel）

Youcantrythefollowingcodeonyourcomputerandchangesomevalues

packagemain

importfmt

funcmain()

c=make(chanint2)change2to1willhaveruntimeerrorbut3isfine

fmtPrintln(lt-c)

RangeandCloseWecanuserangetooperateonbufferchannelsasinsliceandmap

packagemain

import(

funcfibonacci(nintcchanint)

fori=0iltni++

xy=yx+y

close(c)

funcmain()

c=make(chanint10)

gofibonacci(cap(c)c)

fori=rangec

fmtPrintln(i)

fori=rangecwillnotstopreadingdatafromchanneluntilthechannelisclosedWeusethekeywordclosetoclosethechannelinaboveexampleItsimpossibletosendorreceivedataonaclosedchannelyoucanusevok=lt-chtotestifachannelisclosedIfokreturnsfalseitmeansthethereisnodatainthatchannelanditwasclosed

Remembertoalwaysclosechannelsinproducersandnotinconsumersoritsveryeasytogetintopanicstatus

AnotherthingyouneedtorememberisthatchannelsarenotlikefilesYoudonthavetoclosethemfrequentlyunlessyouaresurethechanneliscompletelyuselessoryouwanttoexitrangeloops

SelectIntheaboveexamplesweonlyuseonechannelbuthowcanwedealwithmorethanonechannelGohasakeywordcalledselecttolistentomanychannels

Concurrency

selectisblockingbydefaultanditcontinuestoexecuteonlywhenoneofchannelshasdatatosendorreceiveIfseveralchannelsarereadytouseatthesametimeselectchooseswhichtoexecuterandomly

packagemain

importfmt

funcfibonacci(cquitchanint)

select

caseclt-x

xy=yx+y

caselt-quit

fmtPrintln(quit)

return

funcmain()

c=make(chanint)

quit=make(chanint)

gofunc()

fori=0ilt10i++

fmtPrintln(lt-c)

quitlt-0

fibonacci(cquit)

selecthasadefaultcaseaswelljustlikeswitchWhenallthechannelsarenotreadyforuseitexecutesthedefaultcase(itdoesntwaitforthechannelanymore)

select

casei=lt-c

default

executesherewhencisblocked

TimeoutSometimesagoroutinebecomesblockedHowcanweavoidthistopreventthewholeprogramfromblockingItssimplewecansetatimeoutintheselect

funcmain()

c=make(chanint)

o=make(chanbool)

gofunc()

select

casev=lt-c

println(v)

caselt-timeAfter(5timeSecond)

println(timeout)

olt-true

Concurrency

RuntimegoroutineThepackageruntimehassomefunctionsfordealingwithgoroutines

runtimeGoexit()

Exitsthecurrentgoroutinebutdeferedfunctionswillbeexecutedasusual

runtimeGosched()

Letstheschedulerexecuteothergoroutinesandcomesbackatsomepoint

runtimeNumCPU()int

ReturnsthenumberofCPUcores

runtimeNumGoroutine()int

Returnsthenumberofgoroutines

runtimeGOMAXPROCS(nint)int

SetshowmanyCPUcoresyouwanttouse

LinksDirectoryPrevioussectioninterfaceNextsectionSummary

Concurrency

28SummaryInthischapterwemainlyintroducedthe25GokeywordsLetsreviewwhattheyareandwhattheydo

varandconstareusedtodefinevariablesandconstantspackageandimportareforpackageusefuncisusedtodefinefunctionsandmethodsreturnisusedtoreturnvaluesinfunctionsormethodsdeferisusedtodefinedeferfunctionsgoisusedtostartanewgoroutineselectisusedtoswitchovermultiplechannelsforcommunicationinterfaceisusedtodefineinterfacesstructisusedtodefinespecialcustomizedtypesbreakcasecontinueforfallthroughelseifswitchgotoanddefaultwereintroducedinsection23chanisthetypeofchannelforcommunicationamonggoroutinestypeisusedtodefinecustomizedtypesmapisusedtodefinemapwhichissimilartohashtablesinotherlanguagesrangeisusedforreadingdatafromslicemapandchannel

Ifyouunderstandhowtousethese25keywordsyouvelearnedalotofGoalready

LinksDirectoryPrevioussectionConcurrencyNextchapterWebfoundation

Summary

3WebfoundationThereasonyouarereadingthisbookisthatyouwanttolearntobuildwebapplicationsinGoAsIvesaidbeforeGoprovidesmanypowerfulpackageslikehttpThesepackagescanhelpyoualotwhentryingtobuildwebapplicationsIllteachyoueverythingyouneedtoknowinthefollowingchaptersandwelltalkaboutsomeconceptsofthewebandhowtorunwebapplicationsinGointhischapter

LinksDirectoryPreviouschapterChapter2SummaryNextsectionWebworkingprinciples

Webfoundation

WebworkingprinciplesEverytimeyouopenyourbrowserstypesomeURLsandpressenteryouwillseebeautifulwebpagesappearonyourscreenButdoyouknowwhatishappeningbehindthesesimpleactions

NormallyyourbrowserisaclientAfteryoutypeaURLittakesthehostpartoftheURLandsendsittoaDomainNameServer(DNS)inordertogettheIPaddressofthehostThenitconnectstotheIPaddressandaskstosetupaTCPconnectionThebrowsersendsHTTPrequeststhroughtheconnectionTheserverhandlesthemandreplieswithHTTPresponsescontainingthecontentthatmakeupthewebpageFinallythebrowserrendersthebodyofthewebpageanddisconnectsfromtheserver

Figure31Processesofusersvisitawebsite

AwebserveralsoknownasanHTTPserverusestheHTTPprotocoltocommunicatewithclientsAllwebbrowserscanbeconsideredclients

Wecandividethewebsworkingprinciplesintothefollowingsteps

ClientusesTCPIPprotocoltoconnecttoserverClientsendsHTTPrequestpackagestoserverServerreturnsHTTPresponsepackagestoclientIftherequestedresourcesincludedynamicscriptsservercallsscriptenginefirstClientdisconnectsfromserverstartsrenderingHTML

ThisisasimpleworkflowofHTTPaffairs-noticethattheserverclosesitsconnectionsafteritsendsdatatotheclientsthenwaitsforthenextrequest

URLandDNSresolutionWealwaysuseURLstoaccesswebpagesbutdoyouknowhowURLswork

ThefullnameofaURLisUniformResourceLocatorItsfordescribingresourcesontheinternetanditsbasicformisasfollows

schemehost[port]path[query-string][anchor]

schemeassignunderlyingprotocol(suchasHTTPHTTPSFTP)

hostIPordomainnameofHTTPserver

portdefaultportis80anditcanbeomittedinthiscase

IfyouwanttouseotherportsyoumustspecifywhichportForexample

httpwwwcnblogscom8080

pathresourcespath

query-stringdataaresenttoserver

anchoranchor

DNSisanabbreviationofDomainNameSystemItsthenamingsystemforcomputernetworkservicesanditconvertsdomainnamestoactualIPaddressesjustlikeatranslator

Figure32DNSworkingprinciples

TounderstandmoreaboutitsworkingprincipleletsseethedetailedDNSresolutionprocessasfollows

1 AftertypingthedomainnamewwwqqcominthebrowsertheoperatingsystemwillcheckifthereareanymappingrelationshipsinthehostsfilesforthisdomainnameIfsothenthedomainnameresolutioniscomplete

2 IfnomappingrelationshipsexistinthehostsfilestheoperatingsystemwillcheckifanycacheexistsintheDNSIfso

thenthedomainnameresolutioniscomplete3 IfnomappingrelationshipsexistinboththehostandDNScachetheoperatingsystemfindsthefirstDNSresolution

serverinyourTCPIPsettingswhichislikelyyourlocalDNSserverWhenthelocalDNSserverreceivesthequeryifthedomainnamethatyouwanttoqueryiscontainedwithinthelocalconfigurationofitsregionalresourcesitreturnstheresultstotheclientThisDNSresolutionisauthoritative

4 IfthelocalDNSserverdoesntcontainthedomainnamebutamappingrelationshipexistsinthecachethelocalDNSservergivesbackthisresulttotheclientThisDNSresolutionisnotauthoritative

5 IfthelocalDNSservercannotresolvethisdomainnameeitherbyconfigurationofregionalresourcesorcacheitwillproceedtothenextstepwhichdependsonthelocalDNSserverssettings-IfthelocalDNSserverdoesntenableforwardingitroutestherequesttotherootDNSserverthenreturnstheIPaddressofatoplevelDNSserverwhichmayknowthedomainnamecominthiscaseIfthefirsttoplevelDNSserverdoesntrecognizethedomainnameitagainreroutestherequesttothenexttoplevelDNSserveruntilitreachesonethatrecognizesthedomainnameThenthetoplevelDNSserverasksthisnextlevelDNSserverfortheIPaddresscorrespondingtowwwqqcom-IfthelocalDNSserverhasforwardingenableditsendstherequesttoanupperlevelDNSserverIftheupperlevelDNSserveralsodoesntrecognizethedomainnamethentherequestkeepsgettingreroutedtohigherlevelsuntilitfinallyreachesaDNSserverwhichrecognizesthedomainname

WhetherornotthelocalDNSserverenablesforwardingtheIPaddressofthedomainnamealwaysreturnstothelocalDNSserverandthelocalDNSserversendsitbacktotheclient

Figure33DNSresolutionworkflow

RecursivequeryprocesssimplymeansthattheenquirerschangeintheprocessEnquirersdonotchangeinIterativequeryprocesses

NowweknowclientsgetIPaddressesintheendsothebrowsersarecommunicatingwithserversthroughIPaddresses

HTTPprotocolTheHTTPprotocolisacorepartofwebservicesItsimportanttoknowwhattheHTTPprotocolisbeforeyouunderstandhowthewebworks

HTTPistheprotocolthatisusedtofacilitatecommunicationbetweenbrowserandwebserverItisbasedontheTCPprotocolandusuallyusesport80onthesideofthewebserverItisaprotocolthatutilizestherequest-responsemodel-clientssendrequestsandserversrespondAccordingtotheHTTPprotocolclientsalwayssetupnewconnectionsandsendHTTPrequeststoserversServersarenotabletoconnecttoclientsproactivelyorestablishcallbackconnectionsTheconnectionbetweenaclientandaservercanbeclosedbyeithersideForexampleyoucancancelyourdownloadrequestandHTTPconnectionandyourbrowserwilldisconnectfromtheserverbeforeyoufinishdownloading

TheHTTPprotocolisstatelesswhichmeanstheserverhasnoideaabouttherelationshipbetweenthetwoconnectionseventhoughtheyarebothfromsameclientTosolvethisproblemwebapplicationsusecookiestomaintainthestateofconnections

BecausetheHTTPprotocolisbasedontheTCPprotocolallTCPattackswillaffectHTTPcommunicationsinyourserverExamplesofsuchattacksareSYNfloodingDoSandDDoSattacks

HTTPrequestpackage(browserinformation)

RequestpackagesallhavethreepartsrequestlinerequestheaderandbodyThereisoneblanklinebetweenheaderandbody

GETdomainsexampleHTTP11requestlinerequestmethodURLprotocolanditsversion

Hostwwwianaorgdomainname

User-AgentMozilla50(WindowsNT61)AppleWebKit5374(KHTMLlikeGecko)Chrome220122994Safari5374

browserinformation

Accepttexthtmlapplicationxhtml+xmlapplicationxmlq=09q=08mimethatclientscanaccept

Accept-Encodinggzipdeflatesdchstreamcompression

Accept-CharsetUTF-8q=05charactersetinclientside

blankline

bodyrequestresourcearguments(forexampleargumentsinPOST)

Weusefiddlertogetthefollowingrequestinformation

Figure34InformationofaGETrequestcaughtbyfiddler

Figure35InformationofaPOSTrequestcaughtbyfiddler

WecanseethatGETdoesnothavearequestbodyunlikePOSTwhichdoes

TherearemanymethodsyoucanusetocommunicatewithserversinHTTPGETPOSTPUTandDELETEarethe4basicmethodsthatwetypicallyuseAURLrepresentsaresourceonanetworksothese4methodsdefinethequerychangeaddanddeleteoperationsthatcanactontheseresourcesGETandPOSTareverycommonlyusedinHTTPGETcanappendqueryparameterstotheURLusingtoseparatetheURLandparametersandampbetweentheargumentslikeEditPostsaspxname=test1ampid=123456POSTputsdataintherequestbodybecausetheURLimplementsalengthlimitationviathebrowserThusPOSTcansubmitmuchmoredatathanGETAlsowhenwesubmitusernamesandpasswordswedontwantthiskindofinformationtoappearintheURLsoweusePOSTtokeeptheminvisible

HTTPresponsepackage(serverinformation)Letsseewhatinformationiscontainedintheresponsepackages

HTTP11200OKstatusline

Servernginx108webserversoftwareanditsversionintheservermachine

DateDateTue30Oct2012041425GMTrespondedtime

Content-Typetexthtmlrespondeddatatype

Transfer-Encodingchunkeditmeansdataweresentinfragments

Connectionkeep-alivekeepconnection

Content-Length90lengthofbody

blankline

ltDOCTYPEhtmlPUBLIC-W3CDTDXHTML10TransitionalENmessagebody

ThefirstlineiscalledthestatuslineItsuppliestheHTTPversionstatuscodeandstatusmessage

ThestatuscodeinformstheclientofthestatusoftheHTTPserversresponseInHTTP115kindsofstatuscodesweredefined

-1xxInformational

-2xxSuccess

-3xxRedirection

-4xxClientError

-5xxServerError

Letsseemoreexamplesaboutresponsepackages200meansserverrespondedcorrectly302meansredirection

Figure36Fullinformationforvisitingawebsite

HTTPisstatelessandConnectionkeep-alive

ThetermstatelessdoesntmeanthattheserverhasnoabilitytokeepaconnectionItsimplymeansthattheserverdoesntrecognizeanyrelationshipsbetweenanytworequests

InHTTP11Keep-aliveisusedbydefaultIfclientshaveadditionalrequeststheywillusethesameconnectionforthem

NoticethatKeep-alivecannotmaintainoneconnectionforevertheapplicationrunningintheserverdeterminesthelimitwithwhichtokeeptheconnectionaliveforandinmostcasesyoucanconfigurethislimit

Requestinstance

Figure37Allpackagesforopeningonewebpage

WecanseetheentirecommunicationprocessbetweenclientandserverfromtheabovepictureYoumaynoticethattherearemanyresourcefilesinthelistthesearecalledstaticfilesandGohasspecializedprocessingmethodsforthesefiles

ThisisthemostimportantfunctionofbrowserstorequestforaURLandretrievedatafromwebserversthenrendertheHTMLIfitfindssomefilesintheDOMsuchasCSSorJSfilesbrowserswillrequesttheseresourcesfromtheserveragainuntilalltheresourcesfinishrenderingonyourscreen

ReducingHTTPrequesttimesisonewayofimprovingtheloadingspeedofwebpagesByreducingthenumberofCSSandJSfilesthatneedtobeloadedbothrequestlatenciesandpressureonyourwebserverscanbereducedatthesametime

LinksDirectoryPrevioussectionWebfoundationNextsectionBuildasimplewebserver

32BuildasimplewebserverWevediscussedthatwebapplicationsarebasedontheHTTPprotocolandGoprovidesfullHTTPsupportinthenethttppackageItsveryeasytosetawebserverupusingthispackage

Usehttppackagesetupawebserver

packagemain

import(

nethttp

strings

funcsayhelloName(whttpResponseWriterrhttpRequest)

rParseForm()parseargumentsyouhavetocallthisbyyourself

fmtPrintln(rForm)printforminformationinserverside

fmtPrintln(pathrURLPath)

fmtPrintln(schemerURLScheme)

fmtPrintln(rForm[url_long])

forkv=rangerForm

fmtPrintln(keyk)

fmtPrintln(valstringsJoin(v))

fmtFprintf(wHelloastaxie)senddatatoclientside

funcmain()

httpHandleFunc(sayhelloName)setrouter

err=httpListenAndServe(9090nil)setlistenport

iferr=nil

logFatal(ListenAndServeerr)

Afterweexecutetheabovecodetheserverbeginslisteningtoport9090inlocalhost

Openyourbrowserandvisithttplocalhost9090YoucanseethatHelloastaxieisonyourscreen

Letstryanotheraddresswithadditionalargumentshttplocalhost9090url_long=111ampurl_long=222

Nowletsseewhathappensonboththeclientandserversides

Youshouldseethefollowinginformationontheserverside

Figure38Serverprintedinformation

Asyoucanseeweonlyneedtocalltwofunctionsinordertobuildasimplewebserver

IfyouareworkingwithPHPyoureprobablyaskingwhetherornotweneedsomethinglikeNginxorApacheTheansweriswedontsinceGolistenstotheTCPportbyitselfandthefunctionsayhelloNameisthelogicfunctionjustlikeacontrollerinPHP

IfyouareworkingwithPythonyoushouldknowtornadoandtheaboveexampleisverysimilartothat

IfyouareworkingwithRubyyoumaynoticeitislikescriptserverinROR(RubyonRails)

WeusedtwosimplefunctionstosetupasimplewebserverinthissectionandthissimpleserveralreadyhasthecapacityforhighconcurrencyoperationsWewilltalkabouthowtoutilizethisinthenexttwosections

LinksDirectoryPrevioussectionWebworkingprinciplesNextsectionHowGoworkswithweb

33HowGoworkswithwebWelearnedtousethenethttppackagetobuildasimplewebserverintheprevioussectionandallthoseworkingprinciplesarethesameasthosewewilltalkaboutinthefirstsectionofthischapter

ConceptsinwebprinciplesRequestrequestdatafromusersincludingPOSTGETCookieandURL

Responseresponsedatafromservertoclients

Connconnectionsbetweenclientsandservers

HandlerRequesthandlinglogicandresponsegeneration

httppackageoperatingmechanismThefollowingpictureshowstheworkflowofaGowebserver

Figure39httpworkflow

1 Createalisteningsocketlistentoaportandwaitforclients2 Acceptrequestsfromclients3 HandlerequestsreadHTTPheaderIftherequestusesPOSTmethodreaddatainthemessagebodyandpassthem

tohandlersFinallysocketreturnsresponsedatatoclients

OnceweknowtheanswerstothethreefollowingquestionsitseasytoknowhowthewebworksinGo

HowdowelistentoaportHowdoweacceptclientrequestsHowdoweallocatehandlers

IntheprevioussectionwesawthatGousesListenAndServetohandlethesestepsinitializeaserverobjectcallnetListen(tcpaddr)tosetupaTCPlistenerandlistentoaspecificaddressandport

Letstakealookatthehttppackagessourcecode

HowGoworkswithweb

Buildversiongo112

func(srvServer)Serve(lnetListener)error

deferlClose()

vartempDelaytimeDurationhowlongtosleeponacceptfailure

rwe=lAccept()

ife=nil

ifneok=e(netError)okampampneTemporary()

iftempDelay==0

tempDelay=5timeMillisecond

tempDelay=2

ifmax=1timeSecondtempDelaygtmax

tempDelay=max

logPrintf(httpAccepterrorvretryinginvetempDelay)

timeSleep(tempDelay)

continue

returne

tempDelay=0

cerr=srvnewConn(rw)

iferr=nil

continue

gocserve()

HowdoweacceptclientrequestsafterwebeginlisteningtoaportInthesourcecodewecanseethatsrvServe(netListener)iscalledtohandleclientrequestsInthebodyofthefunctionthereisaforItacceptsarequestcreatesanewconnectionthenstartsanewgoroutinepassingtherequestdatatothegocserve()goroutineThisishowGosupportshighconcurrencyandeverygoroutineisindependent

HowdoweusespecificfunctionstohandlerequestsconnparsesrequestcReadRequest()atfirstthengetsthecorrespondinghandlerhandler=shsrvHandlerwhichisthesecondargumentwepassedwhenwecalledListenAndServeBecausewepassednilGousesitsdefaulthandlerhandler=DefaultServeMuxSowhatisDefaultServeMuxdoinghereWellitstheroutervariablewhichcancallhandlerfunctionsforspecificURLsDidwesetthisYeswedidWedidthisinthefirstlinewhereweusedhttpHandleFunc(sayhelloName)WereusingthisfunctiontoregistertherouterruleforthepathWhentheURListheroutercallsthefunctionsayhelloNameDefaultServeMuxcallsServerHTTPtogethandlerfunctionsfordifferentpathscallingsayhelloNameinthisspecificcaseFinallytheserverwritesdataandrespondstoclients

Detailedworkflow

Figure310WorkflowofhandlinganHTTPrequest

IthinkyoushouldknowhowGorunswebserversnow

LinksDirectoryPrevioussectionBuildasimplewebserverNextsectionGetintohttppackage

HowGoworkswithweb

34GetintohttppackageInprevioussectionswelearnedabouttheworkflowofthewebandtalkedalittlebitaboutGoshttppackageInthissectionwearegoingtolearnabouttwocorefunctionsinthehttppackageConnandServeMux

goroutineinConnUnlikenormalHTTPserversGousesgoroutinesforeveryjobinitiatedbyConninordertoachievehighconcurrencyandperformancesoeveryjobisindependent

Gousesthefollowingcodetowaitfornewconnectionsfromclients

cerr=srvnewConn(rw)

iferr=nil

continue

gocserve()

Asyoucanseeitcreatesanewgoroutineforeveryconnectionandpassesthehandlerthatisabletoreaddatafromtherequesttothegoroutine

CustomizedServeMuxWeusedGosdefaultrouterinprevioussectionswhendiscussingconnserverwiththerouterpassingrequestdatatoaback-endhandler

Thestructofthedefaultrouter

typeServeMuxstruct

musyncRWMutexbecauseofconcurrencywehavetouseamutexhere

mmap[string]muxEntryrouterruleseverystringmappingtoahandler

ThestructofmuxEntry

typemuxEntrystruct

explicitboolexactmatchornot

hHandler

TheinterfaceofHandler

typeHandlerinterface

ServeHTTP(ResponseWriterRequest)routingimplementer

HandlerisaninterfacebutifthefunctionsayhelloNamedidntimplementthisinterfacethenhowdidweadditashandlerTheanswerliesinanothertypecalledHandlerFuncinthehttppackageWecalledHandlerFunctodefineoursayhelloNamemethodsosayhelloNameimplementedHandleratthesametimeItslikewerecallingHandlerFunc(f)andthefunctionfisforceconvertedtotypeHandlerFunc

Getintohttppackage

typeHandlerFuncfunc(ResponseWriterRequest)

ServeHTTPcallsf(wr)

func(fHandlerFunc)ServeHTTP(wResponseWriterrRequest)

Howdoestheroutercallhandlersafterwesettherouterrules

TheroutercallsmuxhandlerServeHTTP(wr)whenitreceivesrequestsInotherwordsitcallstheServeHTTPinterfaceofthehandlerswhichhaveimplementedit

Nowletsseehowmuxhandlerworks

func(muxServeMux)handler(rRequest)Handler

muxmuRLock()

defermuxmuRUnlock()

Host-specificpatterntakesprecedenceovergenericones

h=muxmatch(rHost+rURLPath)

ifh==nil

h=muxmatch(rURLPath)

ifh==nil

h=NotFoundHandler()

returnh

TherouterusestherequestsURLasakeytofindthecorrespondinghandlersavedinthemapthencallshandlerServeHTTPtoexecutefunctionstohandlethedata

YoushouldunderstandthedefaultroutersworkflowbynowandGoactuallysupportscustomizedroutersThesecondargumentofListenAndServeisforconfiguringcustomizedroutersItsaninterfaceofHandlerThereforeanyrouterthatimplementstheHandlerinterfacecanbeused

Thefollowingexampleshowshowtoimplementasimplerouter

packagemain

import(

nethttp

typeMyMuxstruct

func(pMyMux)ServeHTTP(whttpResponseWriterrhttpRequest)

ifrURLPath==

sayhelloName(wr)

return

httpNotFound(wr)

return

fmtFprintf(wHellomyroute)

funcmain()

mux=ampMyMux

httpListenAndServe(9090mux)

Getintohttppackage

RoutingIfyoudonotwanttouseaRouteryoucanstillachievewhatwewroteintheabovesectionbyreplacingthesecondargumenttoListenAndServetonilandregisteringtheURLsusingaHandleFuncfunctionwhichgoesthroughalltheregisteredURLstofindthebestmatchsocaremustbetakenabouttheorderoftheregistering

samplecode

httpHandleFunc(viewsShowAllTasksFunc)

httpHandleFunc(completeviewsCompleteTaskFunc)

httpHandleFunc(deleteviewsDeleteTaskFunc)

ShowAllTasksFuncisusedtohandletheURLwhichisthedefaultons

TODOaddhttp404error

funcShowAllTasksFunc(whttpResponseWriterrhttpRequest)

ifrMethod==GET

context=dbGetTasks(pending)truewhenyouwantnondeletedtasks

dbisapackagewhichinteractswiththedatabase

ifmessage=

contextMessage=message

homeTemplateExecute(wcontext)

message=

message=Methodnotallowed

httpRedirect(wrhttpStatusFound)

ThisisfineforsimpleapplicationswhichdoesntrequiresparameterizedroutingwhatwhenyouneedthatYoucaneitherusetheexistingtoolkitsorframeworksbutsincethisbookisaboutwritingwebappsingolangwearegoingtoteachhowtohandlethisscenarioaswell

WhenthematchismadeontheHandleFuncfunctiontheURLismatchedsosupposewearewritingatodolistmanagerandwewanttodeleteatasksotheURLwedecideforthatapplicationisdelete1soweregisterthedeleteURLlikethishttpHandleFunc(deleteviewsDeleteTaskFunc)delete1thisURLmatchesclosestwiththedeleteURLthananyotherURLsointherURLpathwegettheentireURLoftherequest

DeleteTaskFuncisusedtodeleteatasktrash=movetorecyclebindelete=permanentdelete

funcDeleteTaskFunc(whttpResponseWriterrhttpRequest)

ifrMethod==DELETE

id=rURLPath[len(delete)]

ifid==all

dbDeleteAll()

iderr=strconvAtoi(id)

iferr=nil

fmtPrintln(err)

err=dbDeleteTask(id)

iferr=nil

message=Errordeletingtask

message=Taskdeleted

Getintohttppackage

linkhttpsgithubcomthewhitetulipTasksblobmasterviewsviewsgoL170-L195

InthisabovemethodwhatwebasicallydoisinthefunctionwhichhandlesthedeleteURLwetakeitscompeleteURLwhichisdelete1thenwetakeasliceofthestringandextracteverythingwhichstartsafterthedeletewordwhichistheactualparameterinthiscaseitis1ThenweusethestrconvpackagetoconvertittoanintegeranddeletethetaskwiththattaskID

InmorecomplexscenariostoowecanusethismethodtheadvantageisthatwedonthavetouseanythirdpartytoolkitbutthenagainthirdpartytoolkitsareusefulintheirownrightyouneedtomakeadecisionwhichmethodyoudpreferNoansweristherightanswer

GocodeexecutionflowLetstakealookatthewholeexecutionflow

CallhttpHandleFunc1 CallHandleFuncofDefaultServeMux2 CallHandleofDefaultServeMux3 Addrouterrulestomap[string]muxEntryofDefaultServeMux

CallhttpListenAndServe(9090nil)1 InstantiateServer2 CallListenAndServemethodofServer3 CallnetListen(tcpaddr)tolistentoport4 Startaloopandacceptrequestsintheloopbody5 InstantiateaConnandstartagoroutineforeveryrequestgocserve()6 Readrequestdatawerr=creadRequest()7 CheckwhetherhandlerisemptyornotifitsemptythenuseDefaultServeMux8 CallServeHTTPofhandler9 ExecutecodeinDefaultServeMuxinthiscase10 ChoosehandlerbyURLandexecutecodeinthathandlerfunctionmuxhandlerServeHTTP(wr)11 HowtochoosehandlerACheckrouterrulesforthisURLBCallServeHTTPinthathandlerifthereisoneCCall

ServeHTTPofNotFoundHandlerotherwise

LinksDirectoryPrevioussectionHowGoworkswithwebNextsectionSummary

Getintohttppackage

35SummaryInthischapterweintroducedHTTPDNSresolutionflowandhowtobuildasimplewebserverThenwetalkedabouthowGoimplementswebserversforusbylookingatthesourcecodeofthenethttppackage

IhopethatyounowknowmuchmoreaboutwebdevelopmentandyoushouldseethatitsquiteeasyandflexibletobuildawebapplicationinGo

LinksDirectoryPrevioussectionGetintohttppackageNextchapterUserform

Summary

4UserformAuserformissomethingthatisverycommonlyusedwhendevelopingwebapplicationsItprovidestheabilitytocommunicatebetweenclientsandserversYoumustbeveryfamiliarwithformsifyouareawebdeveloperifyouareaCC++programmeryoumaywanttoaskwhatisauserform

AformisanareathatcontainsformelementsUserscaninputinformationintoformelementsliketextboxesdropdownlistsradiobuttonscheckboxesetcWeusetheformtagltformgttodefineforms

ltformgt

inputelements

ltformgt

GoalreadyhasmanyconvenientfunctionstodealwithuserformsYoucaneasilygetformdatainHTTPrequestsandtheyareeasytointegrateintoyourownwebapplicationsInsection41wearegoingtotalkabouthowtohandleformdatainGoAlsosinceyoucannottrustanydatacomingfromtheclientsideyoumustfirstvalidatethedatabeforeusingitWellgothroughsomeexamplesabouthowtovalidateformdatainsection42

WesaythatHTTPisstatelessHowcanweidentifythatcertainformsarefromthesameuserAndhowdowemakesurethatoneformcanonlybesubmittedonceWelllookatsomedetailsconcerningcookies(acookieisinformationthatcanbesavedontheclientsideandaddedtotherequestheaderwhentherequestissenttotheserver)inbothsections43and44

Anothercommonuse-caseforformsisuploadingfilesInsection45youwilllearnhowtodothisaswellascontrollingthefileuploadsizebeforeitbeginsuploadinginGo

LinksDirectoryPreviouschapterChapter3SummaryNextsectionProcessforminputs

HTTPForm

41ProcessforminputsBeforewebeginletstakealookatasimpleexampleofatypicaluserformsavedaslogingtplinyourprojectfolder

lthtmlgt

ltheadgt

lttitlegtlttitlegt

ltheadgt

ltbodygt

ltformaction=loginmethod=postgt

Usernameltinputtype=textname=usernamegt

Passwordltinputtype=passwordname=passwordgt

ltinputtype=submitvalue=Logingt

ltformgt

ltbodygt

lthtmlgt

ThisformwillsubmittologinontheserverAftertheuserclickstheloginbuttonthedatawillbesenttotheloginhandlerregisteredbytheserverrouterThenweneedtoknowwhetheritusesthePOSTmethodorGET

ThisiseasytofindoutusingthehttppackageLetsseehowtohandletheformdataontheloginpage

Processforminputs

packagemain

import(

htmltemplate

nethttp

strings

rParseForm()ParseurlparameterspassedthenparsetheresponsepacketforthePOSTbody(requestbody)

attentionIfyoudonotcallParseFormmethodthefollowingdatacannotbeobtainedform

fmtPrintln(rForm)printinformationonserverside

forkv=rangerForm

fmtPrintln(keyk)

fmtFprintf(wHelloastaxie)writedatatoresponse

funclogin(whttpResponseWriterrhttpRequest)

fmtPrintln(methodrMethod)getrequestmethod

ifrMethod==GET

t_=templateParseFiles(logingtpl)

tExecute(wnil)

rParseForm()

logicpartoflogin

fmtPrintln(usernamerForm[username])

fmtPrintln(passwordrForm[password])

funcmain()

httpHandleFunc(sayhelloName)settingrouterrule

httpHandleFunc(loginlogin)

err=httpListenAndServe(9090nil)settinglisteningport

iferr=nil

HereweuserMethodtogettherequestmethodanditreturnsanhttpverb-GETPOSTPUTetc

IntheloginfunctionweuserMethodtocheckwhetheritsaloginpageorloginprocessinglogicInotherwordswechecktoseewhethertheuserissimplyopeningthepageortryingtologinServeshowsthepageonlywhentherequestcomesinviatheGETmethodanditexecutestheloginlogicwhentherequestusesthePOSTmethod

Youshouldseethefollowinginterfaceafteropeninghttp1270019090logininyourbrowser

Figure41Userlogininterface

TheserverwillnotprintanythinguntilafterwetypeinausernameandpasswordbecausethehandlerdoesntparsetheformuntilwecallrParseForm()LetsaddrParseForm()beforefmtPrintln(usernamerForm[username])compileourprogramandtestitagainYouwillfindthattheinformationisprintedontheserversidenow

rFormcontainsalloftherequestargumentsforinstancethequery-stringintheURLandthedatainPOSTandPUTIfthedatahasconflictsforexampleparametersthathavethesamenametheserverwillsavethedataintoaslicewithmultiplevaluesTheGodocumentationstatesthatGowillsavethedatafromGETandPOSTrequestsindifferentplaces

Processforminputs

Trychangingthevalueoftheactionintheformhttp1270019090logintohttp1270019090loginusername=astaxieinthelogingtplfiletestitagainandyouwillseethatthesliceisprintedontheserverside

Figure42Serverprintsrequestdata

ThetypeofrequestFormisurlValueItsavesdatawiththeformatkey=value

v=urlValues

vSet(nameAva)

vAdd(friendJess)

vAdd(friendSarah)

vAdd(friendZoe)

vEncode()==name=Avaampfriend=Jessampfriend=Sarahampfriend=Zoe

fmtPrintln(vGet(name))

fmtPrintln(vGet(friend))

fmtPrintln(v[friend])

TipsRequestshavetheabilitytoaccessformdatausingtheFormValue()methodForexampleyoucanchangerForm[username]torFormValue(username)andGocallsrParseFormautomaticallyNoticethatitreturnsthefirstvalueifthereareargumentswiththesamenameanditreturnsanemptystringifthereisnosuchargument

LinksDirectoryPrevioussectionUserformNextsectionVerificationofinputs

Processforminputs

42VerificationofinputsOneofthemostimportantprinciplesinwebdevelopmentisthatyoucannottrustanythingfromclientsideuserformsYouhavetovalidateallincomingdatabeforeuseitManywebsitesareaffectedbythisproblemwhichissimpleyetcrucial

TherearetwowaysofverifyingformdatathatareincommonuseThefirstisJavaScriptvalidationonthefront-endandthesecondisservervalidationontheback-endInthissectionwearegoingtotalkaboutserversidevalidationinwebdevelopment

RequiredfieldsSometimeswerequirethatusersinputsomefieldsbuttheyfailtocompletethefieldForexampleintheprevioussectionwhenwerequiredausernameYoucanusethelenfunctiontogetthelengthofafieldinordertoensurethatusershaveenteredsomething

iflen(rForm[username][0])==0

codeforemptyfield

rFormtreatsdifferentformelementtypesdifferentlywhentheyareblankForemptytextboxestextareasandfileuploadsitreturnsanemptystringforradiobuttonsandcheckboxesitdoesntevencreatethecorrespondingitemsInsteadyouwillgeterrorsifyoutrytoaccessitThereforeitssafertouserFormGet()togetfieldvaluessinceitwillalwaysreturnemptyifthevaluedoesnotexistOntheotherhandrFormGet()canonlygetonefieldvalueatatimesoyouneedtouserFormtogetthemapofvalues

NumbersSometimesyourequirenumbersratherthanothertextforthefieldvalueForexampleletssaythatyourequiretheageofauserinintegerformonlyie50or10insteadofoldenoughoryoungmanIfwerequireapositivenumberwecanconvertthevaluetotheinttypefirstthenprocessit

getinterr=strconvAtoi(rFormGet(age))

iferr=nil

erroroccurswhenconverttonumberitmaynotanumber

checkrangeofnumber

ifgetintgt100

toobig

Anotherwaytodothisisbyusingregularexpressions

ifm_=regexpMatchString(^[0-9]+$rFormGet(age))m

returnfalse

ForhighperformancepurposesregularexpressionsarenotefficienthoweversimpleregularexpressionsareusuallyfastenoughIfyouarefamiliarwithregularexpressionsitsaveryconvenientwaytoverifydataNoticethatGousesRE2soallUTF-8charactersaresupported

Chinese

Validationofinputs

SometimesweneeduserstoinputtheirChinesenamesandwehavetoverifythattheyalluseChineseratherthanrandomcharactersForChineseverificationregularexpressionsaretheonlyway

ifm_=regexpMatchString(^[x4e00-x9fa5]+$rFormGet(realname))m

returnfalse

EnglishlettersSometimesweneeduserstoinputonlyEnglishlettersForexamplewerequiresomeonesEnglishnamelikeastaxieinsteadofasta谢Wecaneasilyuseregularexpressionstoperformourverification

ifm_=regexpMatchString(^[a-zA-Z]+$rFormGet(engname))m

returnfalse

E-mailaddressIfyouwanttoknowwhetherusershaveenteredvalidE-mailaddressesyoucanusethefollowingregularexpression

ifm_=regexpMatchString(`^([w_]210)(w1)([a-z]24)$`rFormGet(email))m

fmtPrintln(no)

fmtPrintln(yes)

DropdownlistLetssaywerequireanitemfromourdropdownlistbutinsteadwegetavaluefabricatedbyhackersHowdowepreventthisfromhappening

Supposewehavethefollowingltselectgt

ltselectname=fruitgt

ltoptionvalue=applegtappleltoptiongt

ltoptionvalue=peargtpearltoptiongt

ltoptionvalue=bananagtbananaltoptiongt

ltselectgt

Wecanusethefollowingstrategytosanitizeourinput

slice=[]stringapplepearbanana

for_v=rangeslice

ifv==rFormGet(fruit)

returntrue

returnfalse

AllthefunctionsIveshownaboveareinmyopensourceprojectforoperatingonslicesandmapshttpsgithubcomastaxiebeeku

Radiobuttons

Validationofinputs

Ifwewanttoknowwhethertheuserismaleorfemalewemayusearadiobuttonreturning1formaleand2forfemaleHoweversomelittlekidwhojustreadhisfirstbookonHTTPdecidestosendtoyoua3WillyourprogramthrowanexceptionAsyoucanseeweneedtousethesamemethodaswedidforourdropdownlisttomakesurethatonlyexpectedvaluesarereturnedbyourradiobutton

ltinputtype=radioname=gendervalue=1gtMale

ltinputtype=radioname=gendervalue=2gtFemale

Andweusethefollowingcodetovalidatetheinput

slice=[]int12

for_v=rangeslice

ifv==rFormGet(gender)

returntrue

returnfalse

CheckboxesSupposetherearesomecheckboxesforuserinterestsandthatyoudontwantextraneousvalueshereeitherYoucanvalidatetheseasefollows

ltinputtype=checkboxname=interestvalue=footballgtFootball

ltinputtype=checkboxname=interestvalue=basketballgtBasketball

ltinputtype=checkboxname=interestvalue=tennisgtTennis

Inthiscasethesanitizationisalittlebitdifferenttovalidatingthebuttonandcheckboxinputssinceherewegetaslicefromthecheckboxes

slice=[]stringfootballbasketballtennis

a=Slice_diff(rForm[interest]slice)

ifa==nil

returntrue

returnfalse

DateandtimeSupposeyouwantuserstoinputvaliddatesortimesGohasthetimepackageforconvertingyearmonthanddaytotheircorrespondingtimesAfterthatitseasytocheckit

t=timeDate(2009timeNovember1023000timeUTC)

fmtPrintf(GolaunchedatsntLocal())

Afteryouhavethetimeyoucanusethetimepackageformoreoperationsdependingonyourneeds

InthissectionwevediscussedsomecommonmethodsofvalidatingformdataontheserversideIhopethatyounowunderstandmoreaboutdatavalidationinGoespeciallyhowtouseregularexpressionstoyouradvantage

LinksDirectory

Validationofinputs

PrevioussectionProcessforminputsNextsectionCrosssitescripting

Validationofinputs

43CrosssitescriptingTodayswebsiteshavemuchmoredynamiccontentinordertoimproveuserexperiencewhichmeansthatwemustprovidedynamicinformationdependingoneveryindividualsbehaviorUnfortunatelydynamicwebsitesaresusceptibletomaliciousattacksknownasCrosssitescripting(knownasXSS)StaticwebsitesarenotsusceptibletoCrosssitescripting

AttackersofteninjectmaliciousscriptslikeJavaScriptVBScriptActiveXorFlashintothosewebsitesthathaveloopholesOncetheyhavesuccessfullyinjectedtheirscriptsuserinformationcanbestolenandyourwebsitecanbefloodedwithspamTheattackerscanalsochangeusersettingstowhatevertheywant

Ifyouwishtopreventthiskindofattackyoushouldcombinethefollowingtwoapproaches

ValidationofalldatafromuserswhichwetalkedaboutintheprevioussectionCarefullyhandledatathatwillbesenttoclientsinordertopreventanyinjectedscriptsfromrunningonbrowsers

SohowcanwedothesetwothingsinGoFortunatelythehtmltemplatepackagehassomeusefulfunctionstoescapedataasfollows

funcHTMLEscape(wioWriterb[]byte)escapesbtowfuncHTMLEscapeString(sstring)stringreturnsastringafterescapingfromsfuncHTMLEscaper(argsinterface)stringreturnsastringafterescapingfrommultiplearguments

Letschangetheexampleinsection41

fmtPrintln(usernametemplateHTMLEscapeString(rFormGet(username)))printatserverside

fmtPrintln(passwordtemplateHTMLEscapeString(rFormGet(password)))

templateHTMLEscape(w[]byte(rFormGet(username)))respondedtoclients

Ifsomeonetriestoinputtheusernameasltscriptgtalert()ltscriptgtwewillseethefollowingcontentinthebrowser

Figure43JavaScriptafterescaped

FunctionsinthehtmltemplatepackagehelpyoutoescapeallHTMLtagsWhatifyoujustwanttoprintltscriptgtalert()ltscriptgttobrowsersYoushouldusetexttemplateinstead

importtexttemplate

terr=templateNew(foo)Parse(`defineTHelloend`)

err=tExecuteTemplate(outTltscriptgtalert(youhavebeenpwned)ltscriptgt)

Output

Helloltscriptgtalert(youhavebeenpwned)ltscriptgt

OryoucanusethetemplateHTMLtypeVariablecontentwillnotbeescapedifitstypeistemplateHTML

importhtmltemplate

err=tExecuteTemplate(outTtemplateHTML(ltscriptgtalert(youhavebeenpwned)ltscriptgt))

Output

Crosssitescripting

Onemoreexampleofescaping

importhtmltemplate

Output

Helloampltscriptampgtalert(amp39youhavebeenpwnedamp39)ampltscriptampgt

LinksDirectoryPrevioussectionVerificationofinputsNextsectionDuplicatesubmissions

Crosssitescripting

44DuplicatesubmissionsIdontknowifyouveeverseensomeblogsorBBSthathavemorethanonepostthatareexactlythesamebutIcantellyouthatitsbecauseuserssubmittedduplicatepostformsTherearemanythingsthatcancauseduplicatesubmissionssometimesusersjustdoubleclickthesubmitbuttonortheywanttomodifysomecontentafterpostingandpressthebackbuttonInsomecasesitisbytheintentionalactionsofmalicioususersItseasytoseehowduplicatesubmissionscanleadtomanyproblemsThuswehavetouseeffectivemeanstopreventit

ThesolutionistoaddahiddenfieldwithauniquetokentoyourformandtoalwayscheckthistokenbeforeprocessingtheincomingdataAlsoifyouareusingAjaxtosubmitaformuseJavaScripttodisablethesubmitbuttononcetheformhasbeensubmitted

Letsimprovetheexamplefromsection42

ltinputtype=hiddenname=tokenvalue=gt

WeuseanMD5hash(timestamp)togeneratethetokenandaddedittobothahiddenfieldontheclientsideformandasessioncookieontheserverside(Chapter6)Wecanthenusethistokentocheckwhetherornotthisformwassubmitted

ifrMethod==GET

crutime=timeNow()Unix()

h=md5New()

ioWriteString(hstrconvFormatInt(crutime10))

token=fmtSprintf(xhSum(nil))

tExecute(wtoken)

loginrequest

rParseForm()

token=rFormGet(token)

iftoken=

checktokenvalidity

giveerrorifnotoken

fmtPrintln(usernamelengthlen(rForm[username][0]))

fmtPrintln(usernametemplateHTMLEscapeString(rFormGet(username)))printinserverside

templateHTMLEscape(w[]byte(rFormGet(username)))respondtoclient

Figure44Thecontentinbrowserafteraddingatoken

YoucanrefreshthispageandyouwillseeadifferenttokeneverytimeThisensuresthateveryformisunique

FornowyoucanpreventmanyduplicatesubmissionattacksbyaddingtokenstoyourformsbutitcannotpreventalldeceptiveattacksofthistypeThereismuchmoreworkthatneedstobedone

LinksDirectoryPrevioussectionCrosssitescriptingNextsectionFileupload

45FileuploadSupposeyouhaveawebsitelikeInstagramandyouwantuserstouploadtheirbeautifulphotosHowwouldyouimplementthatfunctionality

YouhavetoaddpropertyenctypetotheformthatyouwanttouseforuploadingphotosTherearethreepossiblevaluesforthisproperty

applicationx-www-form-urlencodedTranscodeallcharactersbeforeuploading(default)

multipartform-dataNotranscodingYoumustusethisvaluewhenyourformhasfileuploadcontrols

textplainConvertspacesto+butnotranscodingforspecialcharacters

ThereforetheHTMLcontentofafileuploadformshouldlooklikethis

lthtmlgt

ltheadgt

lttitlegtUploadfilelttitlegt

ltheadgt

ltbodygt

ltformenctype=multipartform-dataaction=http1270019090uploadmethod=postgt

ltinputtype=filename=uploadfilegt

ltinputtype=submitvalue=uploadgt

ltformgt

ltbodygt

lthtmlgt

Weneedtoaddafunctionontheserversidetohandlethisform

httpHandleFunc(uploadupload)

uploadlogic

funcupload(whttpResponseWriterrhttpRequest)

fmtPrintln(methodrMethod)

ifrMethod==GET

h=md5New()

t_=templateParseFiles(uploadgtpl)

tExecute(wtoken)

rParseMultipartForm(32ltlt20)

filehandlererr=rFormFile(uploadfile)

iferr=nil

fmtPrintln(err)

return

deferfileClose()

fmtFprintf(wvhandlerHeader)

ferr=osOpenFile(test+handlerFilenameosO_WRONLY|osO_CREATE0666)

iferr=nil

fmtPrintln(err)

return

deferfClose()

ioCopy(ffile)

Fileupload

AsyoucanseeweneedtocallrParseMultipartFormforuploadingfilesThefunctionParseMultipartFormtakesthemaxMemoryargumentAfteryoucallParseMultipartFormthefilewillbesavedintheservermemorywithmaxMemorysizeIfthefilesizeislargerthanmaxMemorytherestofthedatawillbesavedinasystemtemporaryfileYoucanuserFormFiletogetthefilehandleanduseioCopytosavetoyourfilesystem

YoudontneedtocallrParseFormwhenyouaccessothernon-filefieldsintheformbecauseGowillcallitwhenitsnecessaryAlsocallingParseMultipartFormonceisenough-multiplecallsmakenodifference

Weusethreestepsforuploadingfilesasfollows

1 Addenctype=multipartform-datatoyourform2 CallrParseMultipartFormontheserversidetosavethefileeithertomemoryortoatemporaryfile3 CallrFormFiletogetthefilehandleandsavetothefilesystem

ThefilehandleristhemultipartFileHeaderItusesthefollowingstruct

typeFileHeaderstruct

Filenamestring

HeadertextprotoMIMEHeader

containsfilteredorunexportedfields

Figure45Printinformationonserverafterreceivingfile

ClientsuploadfilesIshowedanexampleofusingaformtoauploadafileWecanimpersonateaclientformtouploadfilesinGoaswell

Fileupload

packagemain

import(

ioioutil

mimemultipart

nethttp

funcpostFile(filenamestringtargetUrlstring)error

bodyBuf=ampbytesBuffer

bodyWriter=multipartNewWriter(bodyBuf)

thisstepisveryimportant

fileWritererr=bodyWriterCreateFormFile(uploadfilefilename)

iferr=nil

fmtPrintln(errorwritingtobuffer)

returnerr

openfilehandle

fherr=osOpen(filename)

iferr=nil

fmtPrintln(erroropeningfile)

returnerr

deferfhClose()

iocopy

_err=ioCopy(fileWriterfh)

iferr=nil

returnerr

contentType=bodyWriterFormDataContentType()

bodyWriterClose()

resperr=httpPost(targetUrlcontentTypebodyBuf)

iferr=nil

returnerr

deferrespBodyClose()

resp_bodyerr=ioutilReadAll(respBody)

iferr=nil

returnerr

fmtPrintln(respStatus)

fmtPrintln(string(resp_body))

returnnil

sampleusage

funcmain()

target_url=httplocalhost9090upload

filename=astaxiepdf

postFile(filenametarget_url)

TheaboveexampleshowsyouhowtouseaclienttouploadfilesItusesmultipartWritetowritefilesintocacheandsendsthemtotheserverthroughthePOSTmethod

IfyouhaveotherfieldsthatneedtowriteintodatalikeusernamecallmultipartWriteFieldasneeded

Fileupload

DirectoryPrevioussectionDuplicatesubmissionsNextsectionSummary

Fileupload

46SummaryInthischapterwemainlylearnedhowtoprocessformdatainGothroughseveralexampleslikelogginginusersanduploadingfilesWealsoemphasizedthatvalidatinguserdataisextremelyimportantforwebsitesecurityandweusedonesectiontotalkabouthowtofilterdatawithregularexpressions

Ihopethatyounowknowmoreaboutthecommunicationprocessbetweenclientandserver

LinksDirectoryPrevioussectionFileuploadNextchapterDatabase

Summary

5DatabaseForwebdevelopersthedatabaseisatthecoreofwebdevelopmentYoucansavealmostanythingintoadatabaseandqueryorupdatedatainsideitlikeuserinformationproductsornewsarticles

GodoesntprovideanydatabasedriversbutitdoeshaveadriverinterfacedefinedinthedatabasesqlpackagePeoplecandevelopdatabasedriversbasedonthatinterfaceInsection51wearegoingtotalkaboutdatabasedriverinterfacedesigninGoInsections52to54IwillintroducesomeSQLdatabasedriverstoyouInsection55IwillpresenttheORM　thatIhavedevelopedwhichisbasedonthedatabasesqlinterfacestandardItiscompatiblewithmostdriversthathaveimplementedthedatabasesqlinterfaceanditmakesiteasytoaccessdatabasesidiomaticallyinGo

NoSQLhasbeenahottopicinrecentyearsMorewebsitesaredecidingtouseNoSQLdatabasesastheirmaindatabaseinsteadofjustforthepurposeofcachingIwillintroduceyoutotwoNoSQLdatabaseswhichareMongoDBandRedisinsection56

LinksDirectoryPreviousChapterChapter4SummaryNextsectiondatabasesqlinterface

Database

51databasesqlinterfaceGodoesntprovideanyofficialdatabasedriversunlikeotherlanguageslikePHPwhichdoHoweveritdoeshavesomedatabasedriverinterfacestandardsfordeveloperstodevelopdatabasedriverswithTheadvantageisthatifyourcodeisdevelopedaccordingtotheseinterfacestandardsyouwillnotneedtochangeanycodeifyourdatabasechangesLetsseewhatthesedatabaseinterfacestandardsare

sqlRegisterThisfunctionisinthedatabasesqlpackageforregisteringdatabasedriverswhenyouusethird-partydatabasedriversAlloftheseshouldcalltheRegister(namestringdriverdriverDriver)functionininit()inordertoregisterthemselves

Letstakealookatthecorrespondingmymysqlandsqlite3drivercode

httpsgithubcommattngo-sqlite3driver

funcinit()

sqlRegister(sqlite3ampSQLiteDriver)

httpsgithubcommikespookmymysqldriver

Driverautomaticallyregisteredindatabasesql

vard=Driverprototcpraddr1270013306

funcinit()

Register(SETNAMESutf8)

sqlRegister(mymysqlampd)

Weseethatallthird-partydatabasedriversimplementthisfunctiontoregisterthemselvesandGousesamaptosaveuserdriversinsideofdatabasesql

vardrivers=make(map[string]driverDriver)

drivers[name]=driver

Thereforethisregistrationfunctioncanregisterasmanydriversasyoumayrequireeachwithdifferentnames

Wealwaysseethefollowingcodewhenweusethird-partydrivers

import(

databasesql

_githubcommattngo-sqlite3

Heretheunderscore(alsoknownasablank)_canbequiteconfusingformanybeginnersbutthisisagreatfeatureinGoWealreadyknowthatthisunderscoreidentifierisusedfordiscardingvaluesfromfunctionreturnsandalsothatyoumustuseallpackagesthatyouveimportedinyourcodeinGoSowhentheblankisusedwithimportitmeansthatyouneedtoexecutetheinit()functionofthatpackagewithoutdirectlyusingitwhichisaperfectfitfortheuse-caseofregisteringdatabasedrivers

driverDriverDriverisaninterfacecontaininganOpen(namestring)methodthatreturnsaConninterface

typeDriverinterface

Open(namestring)(Connerror)

Thisisaone-timeConnwhichmeansitcanonlybeusedoncepergoroutineThefollowingcodewillcauseerrorstooccur

gogoroutineA(Conn)query

gogoroutineB(Conn)insert

BecauseGohasnoideawhichgoroutinedoeswhichoperationthequeryoperationmaygettheresultoftheinsertoperationandvice-versa

Allthird-partydriversshouldhavethisfunctiontoparsethenameofConnandreturnthecorrectresults

driverConnThisisadatabaseconnectioninterfacewithsomemethodsandasivesaidabovethesameConncanonlybeusedoncepergoroutine

typeConninterface

Prepare(querystring)(Stmterror)

Close()error

Begin()(Txerror)

PreparereturnsthepreparestatusofcorrespondingSQLcommandsforqueryinganddeletingetcCloseclosesthecurrentconnectionandcleansresourcesMostthird-partydriversimplementsomekindofconnectionpoolsoyoudontneedtocacheconnectionswhichcancauseunexpectederrorsBeginreturnsaTxthatrepresentsatransactionhandleYoucanuseitforqueryingupdatingrollingbacktransactionsetc

driverStmtThisisareadystatusthatcorrespondswithConnsoitcanonlybeusedoncepergoroutine(asisthecasewithConn)

typeStmtinterface

Close()error

NumInput()int

Exec(args[]Value)(Resulterror)

Query(args[]Value)(Rowserror)

CloseclosesthecurrentconnectionbutstillreturnsrowdataifitisexecutingaqueryoperationNumInputreturnsthenumberofobligateargumentsDatabasedriversshouldchecktheircallersargumentswhentheresultisgreaterthan0anditreturns-1whendatabasedriversdontknowanyobligateargumentExecexecutestheupdateinsertSQLcommandspreparedinPreparereturnsResultQueryexecutestheselectSQLcommandpreparedinPreparereturnsrowdata

driverTx

Generallytransactionhandlesonlyhavesubmitorrollbackmethodsanddatabasedriversonlyneedtoimplementthesetwomethods

typeTxinterface

Commit()error

Rollback()error

driverExecerThisisanoptionalinterface

typeExecerinterface

Exec(querystringargs[]Value)(Resulterror)

IfthedriverdoesntimplementthisinterfacewhenyoucallDBExecitwillautomaticallycallPreparethenreturnStmtAfterthatitexecutestheExecmethodofStmtthenclosesStmt

driverResultThisistheinterfaceforresultsofupdateinsertoperations

typeResultinterface

LastInsertId()(int64error)

RowsAffected()(int64error)

LastInsertIdreturnsauto-incrementIdnumberafteradatabaseinsertoperationRowsAffectedreturnsrowsthatwereaffectedbyqueryoperations

driverRowsThisistheinterfacefortheresultofaqueryoperation

typeRowsinterface

Columns()[]string

Close()error

Next(dest[]Value)error

ColumnsreturnsfieldinformationofdatabasetablesTheslicehasaone-to-onecorrespondencewithSQLqueryfieldsonlyanddoesnotreturnallfieldsofthatdatabasetableCloseclosesRowsiteratorNextreturnsnextdataandassignstodestconvertingallstringsintobytearraysandgetsioEOFerrorifnomoredataisavailable

driverRowsAffectedThisisanaliasofint64butitimplementstheResultinterface

typeRowsAffectedint64

func(RowsAffected)LastInsertId()(int64error)

func(vRowsAffected)RowsAffected()(int64error)

driverValueThisisanemptyinterfacethatcancontainanykindofdata

typeValueinterface

TheValuemustbesomethingthatdriverscanoperateonornilsoitshouldbeoneofthefollowingtypes

float64

[]byte

string[]ExceptRowsNextwhichcannotreturnstring

timeTime

driverValueConverterThisdefinesaninterfaceforconvertingnormalvaluestodriverValue

typeValueConverterinterface

ConvertValue(vinterface)(Valueerror)

Thisinterfaceiscommonlyusedindatabasedriversandhasmanyusefulfeatures

ConvertsdriverValuetoacorrespondingdatabasefieldtypeforexampleconvertsint64touint16ConvertsdatabasequeryresultstodriverValueConvertsdriverValuetoauserdefinedvalueinthescanfunction

driverValuerThisdefinesaninterfaceforreturningdriverValue

typeValuerinterface

Value()(Valueerror)

ManytypesimplementthisinterfaceforconversionbetweendriverValueanditself

AtthispointyoushouldknowabitaboutdevelopingdatabasedriversinGoOnceyoucanimplementinterfacesforoperationslikeadddeleteupdateetcthereareonlyafewproblemsleftrelatedtocommunicatingwithspecificdatabases

databasesqldatabasesqldefinesevenmorehigh-levelmethodsontopofdatabasesqldriverformoreconvenientdatabaseoperationsanditsuggeststhatyouimplementaconnectionpool

typeDBstruct

driverdriverDriver

dsnstring

musyncMutexprotectsfreeConnandclosed

freeConn[]driverConn

closedbool

AsyoucanseetheOpenfunctionreturnsaDBthathasafreeConnandthisisasimpleconnectionpoolItsimplementationisverysimpleanduglyItusesdeferdbputConn(cierr)intheDbpreparefunctiontoputaconnectionintotheconnectionpoolEverytimeyoucalltheConnfunctionitchecksthelengthoffreeConnIfitsgreaterthan0thatmeansthereisareusableconnectionanditdirectlyreturnstoyouOtherwiseitcreatesanewconnectionandreturns

LinksDirectoryPrevioussectionDatabaseNextsectionMySQL

52MySQLTheLAMPstackhasbeenverypopularontheinternetinrecentyearsandtheMinLAMPstandforMySQLMySQLisfamousbecauseitsopensourceandeasytouseAssuchithasbecomethede-factodatabaseintheback-endsofmanywebsites

MySQLdriversThereareacoupleofdriversthatsupportMySQLinGoSomeofthemimplementthedatabasesqlinterfaceandothersusetheirowninterfacestandards

httpsgithubcomgo-sql-drivermysqlsupportsdatabasesqlwritteninpureGohttpsgithubcomziutekmymysqlsupportsdatabasesqlanduserdefinedinterfaceswritteninpureGo

Illusethefirstdriverinthefollowingexamples(Iusethisoneinmypersonalprojectstoo)andIalsorecommendthatyouuseitforthefollowingreasons

ItsanewdatabasedriverandsupportsmorefeaturesItfullysupportsdatabasesqlinterfacestandardsSupportskeep-alivelongconnectionswiththread-safety

SamplesInthefollowingsectionsIllusethesamedatabasetablestructurefordifferentdatabasesthencreateSQLasfollows

CREATETABLE`userinfo`(

`uid`INT(10)NOTNULLAUTO_INCREMENT

`username`VARCHAR(64)NULLDEFAULTNULL

`departname`VARCHAR(64)NULLDEFAULTNULL

`created`DATENULLDEFAULTNULL

PRIMARYKEY(`uid`)

Thefollowingexampleshowshowtooperateonadatabasebasedonthedatabasesqlinterfacestandards

packagemain

import(

_githubcomgo-sql-drivermysql

databasesql

funcmain()

dberr=sqlOpen(mysqlastaxieastaxietestcharset=utf8)

checkErr(err)

insert

stmterr=dbPrepare(INSERTuserinfoSETusername=departname=created=)

checkErr(err)

reserr=stmtExec(astaxie研发部门2012-12-09)

checkErr(err)

iderr=resLastInsertId()

checkErr(err)

fmtPrintln(id)

update

HowtouseMySQL

stmterr=dbPrepare(updateuserinfosetusername=whereuid=)

checkErr(err)

reserr=stmtExec(astaxieupdateid)

checkErr(err)

affecterr=resRowsAffected()

checkErr(err)

fmtPrintln(affect)

rowserr=dbQuery(SELECTFROMuserinfo)

checkErr(err)

forrowsNext()

varuidint

varusernamestring

vardepartmentstring

varcreatedstring

err=rowsScan(ampuidampusernameampdepartmentampcreated)

checkErr(err)

fmtPrintln(uid)

fmtPrintln(username)

fmtPrintln(department)

fmtPrintln(created)

delete

stmterr=dbPrepare(deletefromuserinfowhereuid=)

checkErr(err)

reserr=stmtExec(id)

checkErr(err)

fmtPrintln(affect)

dbClose()

funccheckErr(errerror)

iferr=nil

panic(err)

Letmeexplainafewoftheimportantfunctionshere

sqlOpen()opensaregistereddatabasedriverTheGo-MySQL-DriverregisteredthemysqldriverhereThesecondargumentistheDSN(DataSourceName)thatdefinesinformationpertainingtothedatabaseconnectionItsupportsfollowingformats

userunix(pathtosocket)dbnamecharset=utf8

userpasswordtcp(localhost5555)dbnamecharset=utf8

userpassworddbname

userpasswordtcp([deadbeefcafe]80)dbname

dbPrepare()returnsaSQLoperationthatisgoingtobeexecutedItalsoreturnstheexecutionstatusafterexecutingSQL

dbQuery()executesSQLandreturnsaRowsresultstmtExec()executesSQLthathasbeenpreparedandstoredinStmt

Notethatweusetheformat=topassargumentsThisisnecessaryforpreventingSQLinjectionattacks

HowtouseMySQL

LinksDirectoryPrevioussectiondatabasesqlinterfaceNextsectionSQLite

HowtouseMySQL

53SQLiteSQLiteisanopensourceembeddedrelationaldatabaseIthasaself-containedzero-configurationandtransaction-supporteddatabaseengineItscharacteristicsarehighlyportableeasytousecompactefficientandreliableInmostofcasesyouonlyneedabinaryfileofSQLitetocreateconnectandoperateadatabaseIfyouarelookingforanembeddeddatabasesolutionSQLiteisworthconsideringYoucansaySQLiteistheopensourceversionofAccess

SQLitedriversTherearemanydatabasedriversforSQLiteinGobutmanyofthemdonotsupportthedatabasesqlinterfacestandards

httpsgithubcommattngo-sqlite3supportsdatabasesqlbasedoncgohttpsgithubcomfeyeleanorgosqlite3doesntsupportdatabasesqlbasedoncgohttpsgithubcomphfgo-sqlite3doesntsupportdatabasesqlbasedoncgo

ThefirstdriveristheonlyonethatsupportsthedatabasesqlinterfacestandardinitsSQLitedriversoIusethisinmyprojects-itwillmakeiteasytomigratemycodeinthefutureifIneedto

SamplesWecreatethefollowingSQL

`uid`INTEGERPRIMARYKEYAUTOINCREMENT

`username`VARCHAR(64)NULL

`departname`VARCHAR(64)NULL

`created`DATENULL

Anexample

packagemain

import(

databasesql

funcmain()

dberr=sqlOpen(sqlite3foodb)

checkErr(err)

insert

stmterr=dbPrepare(INSERTINTOuserinfo(usernamedepartnamecreated)values())

checkErr(err)

fmtPrintln(id)

update

checkErr(err)

HowtouseSQLite

checkErr(err)

fmtPrintln(affect)

checkErr(err)

varuidint

varusernamestring

vardepartmentstring

varcreatedtimeTime

forrowsNext()

checkErr(err)

fmtPrintln(uid)

fmtPrintln(created)

rowsClose()goodhabittoclose

delete

checkErr(err)

reserr=stmtExec(id)

checkErr(err)

fmtPrintln(affect)

dbClose()

iferr=nil

panic(err)

YoumayhavenoticedthatthecodeisalmostthesameasintheprevioussectionandthatweonlychangedthenameoftheregistereddriverandcalledsqlOpentoconnecttoSQLiteinadifferentway

Notethatsometimesyoucantusetheforstatementbecauseyoudonthavemorethanonerowthenyoucanusetheifstatement

ifrowsNext()

checkErr(err)

fmtPrintln(uid)

fmtPrintln(created)

AlsoyouhavetodoarowsNext()withoutusingthatyoucantfetchdataintheScanfunction

Transactions

HowtouseSQLite

TheaboveexampleshowshowyoufetchdatafromthedatabasebutwhenyouwanttowriteawebapplicationthenitwillnotonlybenecessarytofetchdatafromthedbbutitwillalsoberequiredtowritedataintoitForthatpurposeyoushouldusetransactionsbecauseforvariousreasonssuchashavingmultiplegoroutineswhichaccessthedatabasethedatabasemightgetlockedThisisundesirableinyourwebapplicationandtheuseoftransactionsiseffectiveinensuringyourdatabaseactivitieseitherpassorfailcompletelydependingoncircumstancesItisclearthatusingtransactionscanpreventalotofthingsfromgoingwrongwiththewebapp

trashSQLerr=databasePrepare(updatetasksetis_deleted=Ylast_modified_at=datetime()whereid=)

iferr=nil

fmtPrintln(err)

txerr=databaseBegin()

iferr=nil

fmtPrintln(err)

_err=txStmt(trashSQL)Exec(id)

iferr=nil

fmtPrintln(doingrollback)

txRollback()

txCommit()

Asitisclearfromtheaboveblockofcodeyoufirstprepareastatementafterwhichyouexecuteitdependingontheoutputofthatexecutionthenyoueitherrollitbackorcommitit

AsafinalnoteonthissectionthereisausefulSQLitemanagementtoolavailablehttpsqlitebrowserorg

LinksDirectoryPrevioussectionMySQLNextsectionPostgreSQL

HowtouseSQLite

54PostgreSQLPostgreSQLisanobject-relationaldatabasemanagementsystemavailableformanyplatformsincludingLinuxFreeBSDSolarisMicrosoftWindowsandMacOSXItisreleasedunderanMIT-stylelicenseandisthusfreeandopensourcesoftwareItslargerthanMySQLbecauseitsdesignedforenterpriseusageasanalternativetoOraclePostgresqlisagoodchoiceforenterprisetypeprojects

PostgreSQLdriversTherearemanydatabasedriversavailableforPostgreSQLHerearethreeexamplesofthem

httpsgithubcomlibpqsupportsdatabasesqlwritteninpureGohttpsgithubcomjbarhamgopgsqldriversupportsdatabasesqlwritteninpureGohttpsgithubcomlxngo-pgsqlsupportsdatabasesqlwritteninpureGo

Iwillusethefirstoneintheexamplesthatfollow

CREATETABLEuserinfo

uidserialNOTNULL

usernamecharactervarying(100)NOTNULL

departnamecharactervarying(500)NOTNULL

Createddate

CONSTRAINTuserinfo_pkeyPRIMARYKEY(uid)

WITH(OIDS=FALSE)

Anexample

packagemain

import(

databasesql

_githubcomlibpq

const(

DB_USER=postgres

DB_PASSWORD=postgres

DB_NAME=test

funcmain()

dbinfo=fmtSprintf(user=spassword=sdbname=ssslmode=disable

DB_USERDB_PASSWORDDB_NAME)

dberr=sqlOpen(postgresdbinfo)

checkErr(err)

deferdbClose()

fmtPrintln(Insertingvalues)

varlastInsertIdint

err=dbQueryRow(INSERTINTOuserinfo(usernamedepartnamecreated)VALUES($1$2$3)returninguidastax

ie研发部门2012-12-09)Scan(amplastInsertId)

HowtousePostgreSQL

checkErr(err)

fmtPrintln(lastinsertedid=lastInsertId)

fmtPrintln(Updating)

stmterr=dbPrepare(updateuserinfosetusername=$1whereuid=$2)

checkErr(err)

reserr=stmtExec(astaxieupdatelastInsertId)

checkErr(err)

fmtPrintln(affectrowschanged)

fmtPrintln(Querying)

checkErr(err)

forrowsNext()

varuidint

varusernamestring

vardepartmentstring

varcreatedtimeTime

checkErr(err)

fmtPrintln(uid|username|department|created)

fmtPrintf(3v|8v|6v|6vnuidusernamedepartmentcreated)

fmtPrintln(Deleting)

stmterr=dbPrepare(deletefromuserinfowhereuid=$1)

checkErr(err)

reserr=stmtExec(lastInsertId)

checkErr(err)

iferr=nil

panic(err)

NotethatPostgreSQLusesthe$1$2formatinsteadofthethatMySQLusesandithasadifferentDSNformatinsqlOpenAnotherthingisthatthePostgreSQLdriverdoesnotsupportsqlResultLastInsertId()Soinsteadofthis

stmterr=dbPrepare(INSERTINTOuserinfo(usernamedepartnamecreated)VALUES($1$2$3))

fmtPrintln(resLastInsertId())

usedbQueryRow()andScan()togetthevalueforthelastinsertedid

err=dbQueryRow(INSERTINTOTABLE_NAMEvalues($1)returninguidVALUE1)Scan(amplastInsertId)

fmtPrintln(lastInsertId)

LinksDirectoryPrevioussectionSQLite

HowtousePostgreSQL

NextsectionDevelopORMbasedonbeedb

HowtousePostgreSQL

55DevelopORMbasedonbeedb(Projectbeedbisnolongermaintainedbutthecodesstillthere)

beedbisanORM(object-relationalmapper)developedinGobymeItusesidiomaticGotooperateondatabasesimplementingstruct-to-databasemappingandactsasalightweightGoORMframeworkThepurposeofdevelopingthisORMisnotonlytohelppeoplelearnhowtowriteanORMbutalsotofindagoodbalancebetweenfunctionalityandperformancewhenitcomestodatapersistence

beedbisanopensourceprojectthatsupportsbasicORMfunctionalitybutdoesntsupportassociationqueries

BecausebeedbsupportsdatabasesqlinterfacestandardsanydriverthatimplementsthisinterfacecanbeusedwithbeedbIvetestedthefollowingdrivers

Mysqlgithubgo-mysql-drivermysql

PostgreSQLgithubcomlibpq

SQLitegithubcommattngo-sqlite3

Mysqlgithubcomziutekmymysqlgodrv

MSADODBgithubcommattngo-adodb

Oraclegithubcommattngo-oci8

ODBCbitbucketorgmiquellamgodbc

InstallationYoucanusegogettoinstallbeedblocally

InitializationFirstyouhavetoimportallthenecessarypackages

import(

databasesql

githubcomastaxiebeedb

Thenyouneedtoopenadatabaseconnectionandcreateabeedbobject(MySQLinthisexample)

dberr=sqlOpen(mymysqltestxiemengjun123456)

iferr=nil

panic(err)

orm=beedbNew(db)

beedbNew()actuallyhastwoargumentsThefirstisthedatabaseobjectandthesecondisforindicatingwhichdatabaseengineyoureusingIfyoureusingMySQLSQLiteyoucanjustskipthesecondargument

OtherwisethisargumentmustbesuppliedForinstanceinthecaseofSQLServer

HowtousebeedbORM

orm=beedbNew(dbmssql)

PostgreSQL

orm=beedbNew(dbpg)

beedbsupportsdebuggingUsethefollowingcodetoenableit

beedbOnDebug=true

NextwehaveastructfortheUserinfodatabasetablethatweusedinprevioussections

typeUserinfostruct

Uidint`PK`iftheprimarykeyisnotidyouneedtoaddtag`PK`foryourcustomizedprimarykey

Usernamestring

Departnamestring

CreatedtimeTime

Beawarethatbeedbauto-convertscamelcasenamestolowersnakecaseForexampleifwehaveUserInfoasthestructnamebeedbwillconvertittouser_infointhedatabaseThesameruleappliestostructfieldnames

InsertdataThefollowingexampleshowsyouhowtousebeedbtosaveastructinsteadofusingrawSQLcommandsWeusethebeedbSavemethodtoapplythechange

varsaveoneUserinfo

saveoneUsername=TestAddUser

saveoneDepartname=TestAddDepartname

saveoneCreated=timeNow()

ormSave(ampsaveone)

YoucanchecksaveoneUidaftertherecordisinserteditsvalueisaself-incrementedIDwhichtheSavemethodtakescareofforyou

beedbprovidesanotherwayofinsertingdatathisisviaGosmaptype

add=make(map[string]interface)

add[username]=astaxie

add[departname]=clouddevelop

add[created]=2012-12-02

ormSetTable(userinfo)Insert(add)

Insertmultipledata

addslice=make([]map[string]interface10)

add2=make(map[string]interface)

add2[username]=astaxie2

add2[departname]=clouddevelop2

add2[created]=2012-12-02

addslice=append(addsliceaddadd2)

ormSetTable(userinfo)InsertBatch(addslice)

HowtousebeedbORM

ThemethodshownaboveissimilartoachainedquerywhichyoushouldbefamiliarwithifyouveeverusedjqueryItreturnstheoriginalORMobjectaftercallsthencontinuesdoingotherjobs

ThemethodSetTabletellstheORMwewanttoinsertourdataintotheuserinfotable

UpdatedataLetscontinueworkingwiththeaboveexampletoseehowtoupdatedataNowthatwehavetheprimarykeyofsaveone(Uid)beedbexecutesanupdateoperationinsteadofinsertinganewrecord

saveoneUsername=UpdateUsername

saveoneDepartname=UpdateDepartname

ormSave(ampsaveone)update

Likebeforeyoucanalsousemapforupdatingdata

t=make(map[string]interface)

t[username]=astaxie

ormSetTable(userinfo)SetPK(uid)Where(2)Update(t)

Letmeexplainsomeofthemethodsusedabove

SetPK()tellstheORMthatuidistheprimarykeyrecordsintheuserinfotableWhere()setsconditionsandsupportsmultipleargumentsIfthefirstargumentisanintegeritsashortformforWhere(ltprimarykeygt=ltvaluegt)Update()methodacceptsamapandupdatesthedatabase

QuerydataThebeedbqueryinterfaceisveryflexibleLetsseesomeexamples

Example1querybyprimarykey

varuserUserinfo

Whereacceptstwoargumentssupportsintegers

ormWhere(uid=27)Find(ampuser)

Example2

varuser2Userinfo

ormWhere(3)Find(ampuser2)shortformthatomitsprimarykey

Example3otherqueryconditions

varuser3Userinfo

Wheretwoargumentsareacceptedwithsupportforchartype

ormWhere(name=john)Find(ampuser3)

Example4morecomplexconditions

varuser4Userinfo

Wherethreeargumentsareaccepted

ormWhere(name=andageltjohn88)Find(ampuser4)

Examplestogetmultiplerecords

HowtousebeedbORM

Example1gets10recordswithidgt3thatstartswithposition20

varallusers[]Userinfo

err=ormWhere(idgt3)Limit(1020)FindAll(ampallusers)

Example2omitsthesecondargumentoflimitsoitstartswith0andgets10records

vartenusers[]Userinfo

err=ormWhere(idgt3)Limit(10)FindAll(amptenusers)

Example3getsallrecords

vareveryone[]Userinfo

err=ormOrderBy(uiddescusernameasc)FindAll(ampeveryone)

AsyoucanseetheLimitmethodisforlimitingthenumberofresults

Limit()supportstwoargumentsthenumberofresultsandthestartingposition0isthedefaultvalueofthestartingpositionOrderBy()isfororderingresultsTheargumentistheordercondition

AlltheexamplesherearesimplymappingrecordstostructsYoucanalsojustputthedataintoamapasfollows

a_=ormSetTable(userinfo)SetPK(uid)Where(2)Select(uidusername)FindMap()

Select()tellsbeedbhowmanyfieldsyouwanttogetfromthedatabasetableIfunspecifiedallfieldsarereturnedbydefaultFindMap()returnsthe[]map[string][]bytetypesoyouneedtoconverttoothertypesyourself

Deletedatabeedbprovidesrichmethodstodeletedata

Example1deleteasinglerecord

saveoneistheoneinaboveexample

ormDelete(ampsaveone)

Example2deletemultiplerecords

alluseristheslicewhichgetsmultiplerecords

ormDeleteAll(ampalluser)

Example3deleterecordsbySQL

ormSetTable(userinfo)Where(uidgt3)DeleteRow()

AssociationqueriesbeedbdoesntsupportjoiningbetweenstructsHoweversincesomeapplicationsneedthisfeaturehereisanimplementation

a_=ormSetTable(userinfo)Join(LEFTuserdetailuserinfouid=userdetailuid)

Where(userinfouid=1)Select(userinfouiduserinfousernameuserdetailprofile)FindMap()

HowtousebeedbORM

WeseeanewmethodcalledJoin()thathasthreearguments

ThefirstargumentTypeofJoinINNERLEFTOUTERCROSSetcThesecondargumentthetableyouwanttojoinwithThethirdargumentjoincondition

GroupByandHavingbeedbalsohasanimplementationofgroupbyandhaving

a_=ormSetTable(userinfo)GroupBy(username)Having(username=astaxie)FindMap()

GroupBy()indicatesthefieldthatisforgroupbyHaving()indicatesconditionsofhaving

FutureIhavereceivedalotoffeedbackonbeedbfrommanypeopleallaroundtheworldandImthinkingaboutreconfiguringthefollowingaspects

ImplementaninterfacedesignsimilartodatabasesqldriverinordertofacilitateCRUDoperationsImplementrelationaldatabaseassociationslikeonetooneonetomanyandmanytomanyHeresasample

typeProfilestruct

Nicknamestring

Mobilestring

typeUserinfostruct

Uidint

PK_Usernamestring

Departnamestring

CreatedtimeTime

ProfileHasOne

Auto-createtablesandindexesImplementaconnectionpoolusinggoroutines

LinksDirectoryPrevioussectionPostgreSQLNextsectionNoSQLdatabase

HowtousebeedbORM

56NoSQLdatabaseANoSQLdatabaseprovidesamechanismforthestorageandretrievalofdatathatuseslooserconsistencymodelsthantypicalrelationaldatabasesinordertoachievehorizontalscalingandhigheravailabilitySomeauthorsrefertothemasNotonlySQLtoemphasizethatsomeNoSQLsystemsdoallowSQL-likequerylanguagestobeused

AstheClanguageofthe21stcenturyGohasgoodsupportforNoSQLdatabasesincludingthepopularredismongoDBCassandraandMembaseNoSQLdatabases

redisredisisakey-valuestoragesystemlikeMemcachedthatsupportsthestringlistsetandzset(orderedset)valuetypes

TherearesomeGodatabasedriversforredis

httpsgithubcomgaryburdredigohttpsgithubcomgo-redisredishttpsgithubcomhoisieredishttpsgithubcomalphazeroGo-Redishttpsgithubcomsimonz05godis

Letsseehowtousethedriverthatredigotooperateonadatabase

packagemain

import(

githubcomgaryburdredigoredis

ossignal

syscall

PoolredisPool

funcinit()

redisHost=6379

Pool=newPool(redisHost)

close()

funcnewPool(serverstring)redisPool

returnampredisPool

MaxIdle3

IdleTimeout240timeSecond

Dialfunc()(redisConnerror)

cerr=redisDial(tcpserver)

iferr=nil

returnnilerr

returncerr

TestOnBorrowfunc(credisConnttimeTime)error

_err=cDo(PING)

returnerr

funcclose()

c=make(chanosSignal1)

signalNotify(cosInterrupt)

signalNotify(csyscallSIGTERM)

signalNotify(csyscallSIGKILL)

gofunc()

PoolClose()

osExit(0)

funcGet(keystring)([]byteerror)

conn=PoolGet()

deferconnClose()

vardata[]byte

dataerr=redisBytes(connDo(GETkey))

iferr=nil

returndatafmtErrorf(errorgetkeysvkeyerr)

returndataerr

funcmain()

testerr=Get(test)

fmtPrintln(testerr)

IforkedthelastofthesepackagesfixedsomebugsanduseditinmyshortURLservice(2millionPVeveryday)

httpsgithubcomastaxiegoredis

LetsseehowtousethedriverthatIforkedtooperateonadatabase

packagemain

import(

githubcomastaxiegoredis

funcmain()

varclientgoredisClient

SetthedefaultportinRedis

clientAddr=1270016379

stringmanipulation

clientSet(a[]byte(hello))

val_=clientGet(a)

fmtPrintln(string(val))

clientDel(a)

listoperation

vals=[]stringabcde

for_v=rangevals

clientRpush(l[]byte(v))

dbvals_=clientLrange(l04)

foriv=rangedbvals

println(istring(v))

clientDel(l)

WecanseethatitisquiteeasytooperateredisinGoandithashighperformanceItsclientcommandsarealmostthesameasredisbuilt-incommands

mongoDBmongoDB(fromhumongous)isanopensourcedocument-orienteddatabasesystemdevelopedandsupportedby10genItispartoftheNoSQLfamilyofdatabasesystemsInsteadofstoringdataintablesasisdoneinaclassicalrelationaldatabaseMongoDBstoresstructureddataasJSON-likedocumentswithdynamicschemas(MongoDBcallstheformatBSON)makingtheintegrationofdataincertaintypesofapplicationseasierandfaster

Figure51MongoDBcomparedtoMysql

ThebestdriverformongoDBiscalledmgoanditispossiblethatitwillbeincludedinthestandardlibraryinthefuture

Installmgo

gogetgopkginmgov2

Hereistheexample

packagemain

import(

gopkginmgov2

gopkginmgov2bson

typePersonstruct

Namestring

Phonestring

funcmain()

sessionerr=mgoDial(server1examplecomserver2examplecom)

iferr=nil

panic(err)

defersessionClose()

OptionalSwitchthesessiontoamonotonicbehavior

sessionSetMode(mgoMonotonictrue)

c=sessionDB(test)C(people)

err=cInsert(ampPersonAle+555381169639

ampPersonCla+555384028510)

iferr=nil

logFatal(err)

result=Person

err=cFind(bsonMnameAle)One(ampresult)

iferr=nil

logFatal(err)

fmtPrintln(PhoneresultPhone)

WecanseethattherearenobigdifferenceswhenitcomestooperatingonmgoorbeedbdatabasestheyarebothbasedonstructsThisistheGowayofdoingthings

LinksDirectoryPrevioussectionDevelopORMbasedonbeedbNextsectionSummary

57SummaryInthischapteryoufirstlearnedaboutthedesignofthedatabasesqlinterfaceandmanythird-partydatabasedriversforvariousdatabasetypesThenIintroducedbeedbanORMforrelationaldatabasestoyouIalsoshowedyousomesampledatabaseoperationsIntheendItalkedaboutafewNoSQLdatabasesWesawthatGoprovidesverygoodsupportforthoseNoSQLdatabases

AfterreadingthischapterIhopethatyouhaveabetterunderstandingofhowtooperatedatabasesinGoThisisthemostimportantpartofwebdevelopmentsoIwantyoutocompletelyunderstandthedesignconceptsofthedatabasesqlinterface

LinksDirectoryPrevioussectionNoSQLdatabaseNextsectionDatastorageandsession

Summary

6DatastorageandsessionsAnimportanttopicinwebdevelopmentisprovidingagooduserexperiencebutthefactthatHTTPisastatelessprotocolseemscontrarytothisspiritHowcanwecontrolthewholeprocessofviewingwebsitesforusersTheclassicsolutionsareusingcookiesandsessionswherecookiesserveastheclientsidemechanismandsessionsaresavedontheserversidewithauniqueidentifierforeverysingleuserNotethatsessionscanbepassedinURLsorcookiesoreveninyourdatabase(whichismuchmoresecurebutmayhamperyourapplicationperformance)

Insection61wearegoingtotalkaboutdifferencesbetweencookiesandsessionsInsection62youlllearnhowtousesessionsinGowithanimplementationofasessionmanagerInsection63wewilltalkaboutsessionhijackingandhowtopreventitwhenyouknowthatsessionscanbesavedanywhereThesessionmanagerwewillimplementinsection63willsavesessionsinmemorybutifweneedtoexpandourapplicationtoallowforsessionsharingitsalwaysbettertosavethesesessionsdirectlyintoourdatabaseWelltalkmoreaboutthisinsection64

LinksDirectoryPreviousChapterChapter5SummaryNextsectionSessionandcookies

61SessionandcookiesSessionsandcookiesaretwoverycommonwebconceptsandarealsoveryeasytomisunderstandHowevertheyareextremelyimportantfortheauthorizationofpagesaswellasforgatheringpagestatisticsLetstakealookatthesetwousecases

SupposeyouwanttocrawlapagethatrestrictspublicaccesslikeatwitterusershomepageforinstanceOfcourseyoucanopenyourbrowserandtypeinyourusernameandpasswordtologinandaccessthatinformationbutso-calledwebcrawlingmeansthatweuseaprogramtoautomatethisprocesswithoutanyhumaninterventionThereforewehavetofindoutwhatisreallygoingonbehindthesceneswhenweuseabrowsertologin

WhenwefirstreceivealoginpageandtypeinausernameandpasswordafterwepresstheloginbuttonthebrowsersendsaPOSTrequesttotheremoteserverTheBrowserredirectstotheuserhomepageaftertheserververifiesthelogininformationandreturnsanHTTPresponseThequestionhereishowdoestheserverknowthatwehaveaccessprivilegesforthedesiredwebpageBecauseHTTPisstatelesstheserverhasnowayofknowingwhetherornotwepassedtheverificationinlaststepTheeasiestandperhapsthemostnaivesolutionistoappendtheusernameandpasswordtotheURLThisworksbutputstoomuchpressureontheserver(theservermustvalidateeveryrequestagainstthedatabase)andcanbedetrimentaltotheuserexperienceAnalternativewayofachievingthisgoalistosavetheusersidentityeitherontheserversideorclientsideusingcookiesandsessions

Cookiesinshortstorehistoricalinformation(includinguserlogininformation)ontheclientscomputerTheclientsbrowsersendsthesecookieseverytimetheuservisitsthesamewebsiteautomaticallycompletingtheloginstepfortheuser

Figure61cookieprinciple

SessionsontheotherhandstorehistoricalinformationontheserversideTheserverusesasessionidtoidentifydifferentsessionsandthesessionidthatisgeneratedbytheservershouldalwaysberandomanduniqueYoucanusecookiesorURLargumentstogettheclientsidentity

Figure62sessionprinciple

CookiesCookiesaremaintainedbybrowsersTheycanbemodifiedduringcommunicationbetweenwebserversandbrowsersWebapplicationscanaccesscookieinformationwhenusersvisitthecorrespondingwebsitesWithinmostbrowsersettingsthereisonesettingpertainingtocookieprivacyYoushouldbeabletoseesomethingsimilartothefollowingwhenyouopenit

Figure63cookieinbrowsers

Cookieshaveanexpirytimeandtherearetwotypesofcookiesdistinguishedbytheirlifecylessessioncookiesandpersistentcookies

IfyourapplicationdoesntsetacookieexpirytimethebrowserwillnotsaveitintothelocalfilesystemafterthebrowserisclosedThesecookiesarecalledsessioncookiesandthistypeofcookieisusuallysavedinmemoryinsteadoftothelocalfilesystem

Ifyourapplicationdoessetanexpirytime(forexamplesetMaxAge(606024))thebrowserwillsavethiscookietothelocalfilesystemanditwillnotbedeleteduntilreachingtheallottedexpirytimeCookiesthataresavedtothelocalfilesystemcanbesharedbydifferentbrowserprocesses-forexamplebytwoIEwindowsdifferentbrowsersusedifferentprocessesfordealingwithcookiesthataresavedinmemory　　

Sessionandcookies

SetcookiesinGoGousestheSetCookiefunctioninthenethttppackagetosetcookies

httpSetCookie(wResponseWritercookieCookie)

wistheresponseoftherequestandcookieisastructLetsseewhatitlookslike

typeCookiestruct

Namestring

Valuestring

Pathstring

Domainstring

ExpirestimeTime

RawExpiresstring

MaxAge=0meansnoMax-Ageattributespecified

MaxAgelt0meansdeletecookienowequivalentlyMax-Age0

MaxAgegt0meansMax-Ageattributepresentandgiveninseconds

MaxAgeint

Securebool

HttpOnlybool

Rawstring

Unparsed[]stringRawtextofunparsedattribute-valuepairs

Hereisanexampleofsettingacookie

expiration=timeNow()Add(36524timeHour)

cookie=httpCookieNameusernameValueastaxieExpiresexpiration

httpSetCookie(wampcookie)

FetchcookiesinGoTheaboveexampleshowshowtosetacookieNowletsseehowtogetacookiethathasbeenset

cookie_=rCookie(username)

fmtFprint(wcookie)

Hereisanotherwaytogetacookie

for_cookie=rangerCookies()

fmtFprint(wcookieName)

Asyoucanseeitsveryconvenienttogetcookiesfromrequests

SessionsAsessionisaseriesofactionsormessagesForexampleyoucanthinkoftheactionsyoubetweenpickingupyourtelephonetohanginguptobeatypeofsessionWhenitcomestonetworkprotocolssessionshavemoretodowithconnectionsbetweenbrowsersandservers

Sessionshelptostoretheconnectionstatusbetweenserverandclientandthiscansometimesbeintheformofadatastoragestruct

Sessionandcookies

Sessionsareaserver-sidemechanismandusuallyemployhashtables(orsomethingsimilar)tosaveincominginformation

WhenanapplicationneedstoassignanewsessiontoaclienttheservershouldcheckifthereareanyexistingsessionsforthesameclientwithauniquesessionidIfthesessionidalreadyexiststheserverwilljustreturnthesamesessiontotheclientOntheotherhandifasessioniddoesntexistfortheclienttheservercreatesabrandnewsession(thisusuallyhappenswhentheserverhasdeletedthecorrespondingsessionidbuttheuserhasappendedtheoldsessionmanually)

Thesessionitselfisnotcomplexbutitsimplementationanddeploymentaresoyoucannotuseonewaytorulethemall

SummaryInconclusionthepurposeofsessionsandcookiesarethesameTheyarebothforovercomingthestatelessnessofHTTPbuttheyusedifferentmethodsSessionsusecookiestosavesessionidsontheclientsideandsaveallotherinformationontheserversideCookiessaveallclientinformationontheclientsideYoumayhavenoticedthatcookieshavesomesecurityproblemsForexampleusernamesandpasswordscanpotentiallybecrackedandcollectedbymaliciousthirdpartywebsites

Herearetwocommonexploits

1 appAsettinganunexpectedcookieforappB2 XSSattackappAusestheJavaScriptdocumentcookietoaccessthecookiesofappB

AfterfinishingthissectionyoushouldknowsomeofthebasicconceptsofcookiesandsessionsYoushouldbeabletounderstandthedifferencesbetweenthemsothatyouwontkillyourselfwhenbugsinevitablyemergeWelldiscusssessionsinmoredetailinthefollowingsections

LinksDirectoryPrevioussectionDatastorageandsessionNextsectionHowtousesessioninGo

Sessionandcookies

62HowtousesessionsinGoInsection61welearnedthatsessionsareonesolutionforverifyingusersandthatfornowtheGostandardlibrarydoesnothavebaked-insupportforsessionsorsessionhandlingSoweregoingtoimplementourownversionofasessionmanagerinGo

CreatingsessionsThebasicprinciplebehindsessionsisthataservermaintainsinformationforeverysingleclientandclientsrelyonuniquesessionidstoaccessthisinformationWhenusersvisitthewebapplicationtheserverwillcreateanewsessionwiththefollowingthreestepsasneeded

CreateauniquesessionidOpenupadatastoragespacenormallywesavesessionsinmemorybutyouwillloseallsessiondataifthesystemisaccidentallyinterruptedThiscanbeaveryseriousissueifwebapplicationdealswithsensitivedatalikeinelectroniccommerceforinstanceInordertosolvethisproblemyoucaninsteadsaveyoursessiondatainadatabaseorfilesystemThismakesdatapersistencemorereliableandeasytosharewithotherapplicationsalthoughthetradeoffisthatmoreserver-sideIOisneededtoreadandwritethesesessionsSendtheuniquesessionidtotheclient

ThekeystephereistosendtheuniquesessionidtotheclientInthecontextofastandardHTTPresponseyoucaneitherusetheresponselineheaderorbodytoaccomplishthisthereforewehavetwowaystosendsessionidstoclientsbycookiesorURLrewrites

CookiestheservercaneasilyuseSet-cookieinsideofaresponseheadertosendasessionidtoaclientandaclientcanthenusethiscookieforfuturerequestsweoftensettheexpirytimeforcookiescontainingsessioninformationto0whichmeansthecookiewillbesavedinmemoryandonlydeletedafterusershaveclosetheirbrowsersURLrewriteappendthesessionidasargumentsintheURLforallpagesThiswayseemsmessybutitsthebestchoiceifclientshavedisabledcookiesintheirbrowsers

UseGotomanagesessionsWevetalkedaboutconstructingsessionsandyoushouldnowhaveageneraloverviewofitbuthowcanweusesessionsondynamicpagesLetstakeacloserlookatthelifecycleofasessionsowecancontinueimplementingourGosessionmanager

Sessionmanagementdesign

Hereisalistofsomeofthekeyconsiderationsinsessionmanagementdesign

GlobalsessionmanagerKeepsessioniduniqueHaveonesessionforeveryuserSessionstorageinmemoryfileordatabaseDealwithexpiredsessions

NextwellexamineacompleteexampleofaGosessionmanagerandtherationalebehindsomeofitsdesigndecisions

Sessionmanager

Defineaglobalsessionmanager

HowtousesessioninGo

typeManagerstruct

cookieNamestringprivatecookiename

locksyncMutexprotectssession

providerProvider

maxlifetimeint64

funcNewManager(provideNamecookieNamestringmaxlifetimeint64)(Managererror)

providerok=provides[provideName]

returnnilfmtErrorf(sessionunknownprovideq(forgottenimport)provideName)

returnampManagerproviderprovidercookieNamecookieNamemaxlifetimemaxlifetimenil

Createaglobalsessionmanagerinthemain()function

varglobalSessionssessionManager

Theninitializethesessionmanager

funcinit()

globalSessions=NewManager(memorygosessionid3600)

WeknowthatwecansavesessionsinmanywaysincludinginmemorythefilesystemordirectlyintothedatabaseWeneedtodefineaProviderinterfaceinordertorepresenttheunderlyingstructureofoursessionmanager

typeProviderinterface

SessionInit(sidstring)(Sessionerror)

SessionRead(sidstring)(Sessionerror)

SessionDestroy(sidstring)error

SessionGC(maxLifeTimeint64)

SessionInitimplementstheinitializationofasessionandreturnsanewsessionifitsucceedsSessionReadreturnsasessionrepresentedbythecorrespondingsidCreatesanewsessionandreturnsitifitdoesnotalreadyexistSessionDestroygivenansiddeletesthecorrespondingsessionSessionGCdeletesexpiredsessionvariablesaccordingtomaxLifeTime

SowhatmethodsshouldoursessioninterfacehaveIfyouhaveanyexperienceinwebdevelopmentyoushouldknowthatthereareonlyfouroperationsforsessionssetvaluegetvaluedeletevalueandgetcurrentsessionidSooursessioninterfaceshouldhavefourmethodstoperformtheseoperations

typeSessioninterface

Set(keyvalueinterface)errorsetsessionvalue

Get(keyinterface)interfacegetsessionvalue

Delete(keyinterface)errordeletesessionvalue

SessionID()stringbackcurrentsessionID

ThisdesigntakesitsrootsfromthedatabasesqldriverwhichdefinestheinterfacefirstthenregistersspecificstructureswhenwewanttouseitThefollowingcodeistheinternalimplementationofasessionregisterfunction

HowtousesessioninGo

varprovides=make(map[string]Provider)

Registermakesasessionprovideravailablebytheprovidedname

IfaRegisteriscalledtwicewiththesamenameorifthedriverisnil

itpanics

funcRegister(namestringproviderProvider)

ifprovider==nil

panic(sessionRegisterproviderisnil)

if_dup=provides[name]dup

panic(sessionRegistercalledtwiceforprovider+name)

provides[name]=provider

UniquesessionidsSessionidsareforidentifyingusersofwebapplicationssotheymustbeuniqueThefollowingcodeshowshowtoachievethisgoal

func(managerManager)sessionId()string

b=make([]byte32)

if_err=ioReadFull(randReaderb)err=nil

return

returnbase64URLEncodingEncodeToString(b)

CreatingasessionWeneedtoallocateorgetanexistingsessioninordertovalidateuseroperationsTheSessionStartfunctionisforcheckingtheexistenceofanysessionsrelatedtothecurrentuserandcreatinganewsessionifnoneisfound

func(managerManager)SessionStart(whttpResponseWriterrhttpRequest)(sessionSession)

managerlockLock()

defermanagerlockUnlock()

cookieerr=rCookie(managercookieName)

iferr=nil||cookieValue==

sid=managersessionId()

session_=managerproviderSessionInit(sid)

cookie=httpCookieNamemanagercookieNameValueurlQueryEscape(sid)PathHttpOnlytrueM

axAgeint(managermaxlifetime)

sid_=urlQueryUnescape(cookieValue)

session_=managerproviderSessionRead(sid)

return

Hereisanexamplethatusessessionsforaloginoperation

sess=globalSessionsSessionStart(wr)

rParseForm()

ifrMethod==GET

wHeader()Set(Content-Typetexthtml)

tExecute(wsessGet(username))

sessSet(usernamerForm[username])

httpRedirect(wr302)

HowtousesessioninGo

Operationvaluesetgetanddelete

TheSessionStartfunctionreturnsavariablethatimplementsasessioninterfaceHowdoweuseit

YousawsessionGet(uid)intheaboveexampleforabasicoperationNowletsexamineamoredetailedexample

funccount(whttpResponseWriterrhttpRequest)

createtime=sessGet(createtime)

ifcreatetime==nil

sessSet(createtimetimeNow()Unix())

elseif(createtime(int64)+360)lt(timeNow()Unix())

globalSessionsSessionDestroy(wr)

ct=sessGet(countnum)

ifct==nil

sessSet(countnum1)

sessSet(countnum(ct(int)+1))

t_=templateParseFiles(countgtpl)

tExecute(wsessGet(countnum))

AsyoucanseeoperatingonsessionssimplyinvolvesusingthekeyvaluepatternintheSetGetandDeleteoperations

BecausesessionshavetheconceptofanexpirytimewedefinetheGCtoupdatethesessionslatestmodifytimeThiswaytheGCwillnotdeletesessionsthathaveexpiredbutarestillbeingused

ResetsessionsWeknowthatwebapplicationshavealogoutoperationWhenuserslogoutweneedtodeletethecorrespondingsessionWevealreadyusedtheresetoperationinaboveexample-nowletstakealookatthefunctionbody

Destroysessionid

func(managerManager)SessionDestroy(whttpResponseWriterrhttpRequest)

return

managerlockLock()

managerproviderSessionDestroy(cookieValue)

expiration=timeNow()

cookie=httpCookieNamemanagercookieNamePathHttpOnlytrueExpiresexpirationMaxAge-1

Deletesessions

LetsseehowtoletthesessionmanagerdeleteasessionWeneedtostarttheGCinthemain()function

HowtousesessioninGo

funcinit()

goglobalSessionsGC()

func(managerManager)GC()

managerlockLock()

managerproviderSessionGC(managermaxlifetime)

timeAfterFunc(timeDuration(managermaxlifetime)func()managerGC())

WeseethattheGCmakesfulluseofthetimerfunctioninthetimepackageItautomaticallycallsGCwhenthesessiontimesoutensuringthatallsessionsareusableduringmaxLifeTimeAsimilarsolutioncanbeusedtocountonlineusers

SummarySofarweimplementedasessionmanagertomanageglobalsessionsinthewebapplicationanddefinedtheProviderinterfaceasthestorageimplementationofSessionInthenextsectionwearegoingtotalkabouthowtoimplementProviderforadditionalsessionstoragestructureswhichyouwillbeabletoreferenceinthefuture

LinksDirectoryPrevioussectionSessionandcookiesNextsectionSessionstorage

HowtousesessioninGo

63SessionstorageWeintroducedasimplesessionmanagersworkingprinciplesintheprevioussectionandamongotherthingswedefinedasessionstorageinterfaceInthissectionImgoingtoshowyouanexampleofamemorybasedsessionstorageenginethatimplementsthisinterfaceYoucantailorthistootherformsofsessionstorageaswell

packagememory

import(

containerlist

githubcomastaxiesession

varpder=ampProviderlistlistNew()

typeSessionStorestruct

sidstringuniquesessionid

timeAccessedtimeTimelastaccesstime

valuemap[interface]interfacesessionvaluestoredinside

func(stSessionStore)Set(keyvalueinterface)error

stvalue[key]=value

pderSessionUpdate(stsid)

returnnil

func(stSessionStore)Get(keyinterface)interface

ifvok=stvalue[key]ok

returnv

returnnil

func(stSessionStore)Delete(keyinterface)error

delete(stvaluekey)

returnnil

func(stSessionStore)SessionID()string

returnstsid

typeProviderstruct

locksyncMutexlock

sessionsmap[string]listElementsaveinmemory

listlistListgc

func(pderProvider)SessionInit(sidstring)(sessionSessionerror)

pderlockLock()

deferpderlockUnlock()

v=make(map[interface]interface0)

newsess=ampSessionStoresidsidtimeAccessedtimeNow()valuev

element=pderlistPushBack(newsess)

pdersessions[sid]=element

returnnewsessnil

func(pderProvider)SessionRead(sidstring)(sessionSessionerror)

ifelementok=pdersessions[sid]ok

Sessionstorage

returnelementValue(SessionStore)nil

sesserr=pderSessionInit(sid)

returnsesserr

returnnilnil

func(pderProvider)SessionDestroy(sidstring)error

delete(pdersessionssid)

pderlistRemove(element)

returnnil

func(pderProvider)SessionGC(maxlifetimeint64)

pderlockLock()

element=pderlistBack()

ifelement==nil

if(elementValue(SessionStore)timeAccessedUnix()+maxlifetime)lttimeNow()Unix()

delete(pdersessionselementValue(SessionStore)sid)

func(pderProvider)SessionUpdate(sidstring)error

pderlockLock()

elementValue(SessionStore)timeAccessed=timeNow()

pderlistMoveToFront(element)

returnnil

funcinit()

pdersessions=make(map[string]listElement0)

sessionRegister(memorypder)

TheaboveexampleimplementsamemorybasedsessionstoragemechanismItusesitsinit()functiontoregisterthisstorageenginetothesessionmanagerSohowdoweregisterthisenginefromourmainprogram

import(

_githubcomastaxiesessionprovidersmemory

Weusetheblankimportmechanism(whichwillinvokethepackagesinit()functionautomatically)toregisterthisenginetoasessionmanagerWethenusethefollowingcodetoinitializethesessionmanager

Sessionstorage

initializeininit()function

funcinit()

globalSessions_=sessionNewManager(memorygosessionid3600)

LinksDirectoryPrevioussectionHowtousesessionsinGoNextsectionPreventsessionhijacking

Sessionstorage

64PreventingsessionhijackingSessionhijackingisacommonyetserioussecuritythreatClientsusesessionidsforvalidationandotherpurposeswhencommunicatingwithserversUnfortunatelymaliciousthirdpartiescansometimestrackthesecommunicationsandfigureouttheclientsessionid

Inthissectionwearegoingtoshowyouhowtohijackasessionforeducationalpurposes

ThesessionhijackingprocessThefollowingcodeisacounterforthecountvariable

ifct==nil

sessSet(countnum1)

Thecontentofcountgtplisasfollows

HiNowcount

Wecanseethefollowingcontentinthebrowser

Figure64countinbrowser

Keeprefreshinguntilthenumberbecomes6thenopenthebrowserscookiemanager(Iusechromehere)Youshouldbeabletoseethefollowinginformation

Figure65cookiessavedinabrowser

Thisstepisveryimportantopenanotherbrowser(Iusefirefoxhere)copytheURLtothenewbrowseropenacookiesimulatortocreateanewcookieandinputexactlythesamevalueasthecookiewesawinourfirstbrowser

Figure66Simulateacookie

Refreshthepageandyoullseethefollowing

Figure67hijackingthesessionhassucceeded

HereweseethatwecanhijacksessionsbetweendifferentbrowsersandactionsperformedinonebrowsercanaffectthestateofapageinanotherbrowserBecauseHTTPisstatelessthereisnowayofknowingthatthesessionidfromfirefoxissimulatedandchromeisalsonotabletoknowthatitssessionidhasbeenhijacked

preventsessionhijacking

cookieonlyandtoken

ThroughthissimpleexampleofhijackingasessionyoucanseethatitsverydangerousbecauseitallowsattackerstodowhatevertheywantSohowcanwepreventsessionhijacking

ThefirststepistoonlysetsessionidsincookiesinsteadofinURLrewritesAlsoweshouldsetthehttponlycookiepropertytotrueThisrestrictsclient-sidescriptsfromgainingaccesstothesessionidUsingthesetechniquescookiescannotbeaccessedbyXSSanditwontbeaseasyaswedemonstratedtogetasessionidfromacookiemanager

ThesecondstepistoaddatokentoeveryrequestSimilartothemannerinwhichwedealtwithrepeatingformsubmissionsinprevioussectionsweaddahiddenfieldthatcontainsatokenWhenarequestissenttotheserverwecanverifythistokentoprovethattherequestisunique

h=md5New()

salt=astaxie^7amp8888

ioWriteString(hsalt+timeNow()String())

ifrForm[token]=token

asktologin

sessSet(tokentoken)

SessionidtimeoutAnothersolutionistoaddacreatetimeforeverysessionandtoreplaceexpiredsessionidswithnewonesThiscanpreventsessionhijackingundercertaincircumstancessuchaswhenthehijackisattemptedtoolate

ifcreatetime==nil

Wesetavaluetosavethecreatetimeandcheckifitsexpired(Iset60secondshere)Thisstepcanoftenthwartsessionhijackingattempts

BycombiningthetwosolutionssetoutaboveyouwillbeabletopreventmostsessionhijackingattemptsfromsucceedingOntheonehandsessionidsthatarefrequentlyresetwillresultinanattackeralwaysgettingexpiredanduselesssessionidsontheotherhandbysettingthehttponlypropertyoncookiesandensuringthatsessionidscanonlybepassedviacookiesallURLbasedattacksaremitigatedFinallywesetMaxAge=0onourcookieswhichmeansthatthesessionidswillnotbesavedinthebrowserhistory

LinksDirectoryPrevioussectionSessionstorageNextsectionSummary

65SummaryInthischapterwelearnedaboutthedefinitionandpurposeofsessionsandcookiesandtherelationshipbetweenthetwoSinceGodoesntsupportsessionsinitsstandardlibrarywealsodesignedourownsessionmanagerWewentthrougheverythingfromcreatingclientsessionstodeletingthemWethendefinedaninterfacecalledProviderwhichsupportsallsessionstoragestructuresInsection63weimplementedamemorybasedsessionmanagertopersistclientdataacrosssessionsInsection64IdemonstratedonewayofhijackingasessionThenwelookedathowtopreventyourownsessionsfrombeinghijackedIhopethatyounowunderstandmostoftheworkingprinciplesbehindsessionssothatyoureabletosafelyusetheminyourapplications

LinksDirectoryPrevioussectionPreventsessionhijackingNextchapterTextfiles

Summary

7TextfilesHandlingtextfilesisabigpartofwebdevelopmentWeoftenneedtoproduceorhandlereceivedtextcontentincludingstringsnumbersJSONXMLetcAsahighperformancelanguageGohasgoodsupportforthisinitsstandardlibraryYoullfindthatthesesupportinglibrariesarejustawesomeandwillallowyoutoeasilydealwithanytextcontentyoumayencounterThischaptercontains4sectionsandwillgiveyouafullintroductiontotextprocessinginGo

XMLisaninteractivelanguagethatiscommonlyusedinmanyAPIsmanywebserverswritteninJavauseXMLastheirstandardinteractionlanguageWellmoretalkaboutXMLinsection71Insection72welltakealookatJSONwhichhasbeenverypopularinrecentyearsandismuchmoreconvenientthanXMLInsection73wearegoingtotalkaboutregularexpressionswhich(forthemajorityofpeople)lookslikealanguageusedbyaliensInsection74youwillseehowtheMVCpatternisusedtodevelopapplicationsinGoandalsohowtouseGostemplatepackagefortemplatingyourviewsInsection75wellintroduceyoutofileandfolderoperationsFinallywewillexplainsomeGostringoperationsinsection76

LinksDirectoryPreviousChapterChapter6SummaryNextsectionXML

Textfiles

71XMLXMLisacommonlyuseddatacommunicationformatinwebservicesTodayitsassumingamoreandmoreimportantroleinwebdevelopmentInthissectionweregoingtointroducehowtoworkwithXMLthroughGosstandardlibrary

IwillnotmakeanyattemptstoteachXMLssyntaxorconventionsForthatpleasereadmoredocumentationaboutXMLitselfWewillonlyfocusonhowtoencodeanddecodeXMLfilesinGo

SupposeyouworkinITandyouhavetodealwiththefollowingXMLconfigurationfile

ltxmlversion=10encoding=utf-8gt

ltserversversion=1gt

ltservergt

ltserverNamegtShanghai_VPNltserverNamegt

ltserverIPgt127001ltserverIPgt

ltservergt

ltserverNamegtBeijing_VPNltserverNamegt

ltservergt

ltserversgt

TheaboveXMLdocumentcontainstwokindsofinformationaboutyourservertheservernameandIPWewillusethisdocumentinourfollowingexamples

ParseXMLHowdoweparsethisXMLdocumentWecanusetheUnmarshalfunctioninGosxmlpackagetodothis

funcUnmarshal(data[]bytevinterface)error

thedataparameterreceivesadatastreamfromanXMLsourceandvisthestructureyouwanttooutputtheparsedXMLtoItisaninterfacewhichmeansyoucanconvertXMLtoanystructureyoudesireHerewellonlytalkabouthowtoconvertfromXMLtothestructtypesincetheysharesimilartreestructures

Samplecode

packagemain

import(

encodingxml

ioioutil

typeRecurlyserversstruct

XMLNamexmlName`xmlservers`

Versionstring`xmlversionattr`

Svs[]server`xmlserver`

Descriptionstring`xmlinnerxml`

typeserverstruct

XMLNamexmlName`xmlserver`

ServerNamestring`xmlserverName`

ServerIPstring`xmlserverIP`

funcmain()

fileerr=osOpen(serversxml)Forreadaccess

iferr=nil

fmtPrintf(errorverr)

return

deferfileClose()

dataerr=ioutilReadAll(file)

iferr=nil

return

v=Recurlyservers

err=xmlUnmarshal(dataampv)

iferr=nil

return

fmtPrintln(v)

XMLisactuallyatreedatastructureandwecandefineaverysimilarstructureusingstructsinGothenusexmlUnmarshaltoconvertfromXMLtoourstructobjectThesamplecodewillprintthefollowingcontent

servers1[serverShanghai_VPN127001serverBeijing_VPN127002]

ltservergt

WeusexmlUnmarshaltoparsetheXMLdocumenttothecorrespondingstructobjectYoushouldseethatwehavesomethinglikexmlserverNameinourstructThisisafeatureofstructscalledstructtagsforhelpingwithreflectionLetsseethedefinitionofUnmarshalagain

ThefirstargumentisanXMLdatastreamThesecondargumentisstoragetypeandsupportsthestructsliceandstringtypesGosXMLpackageusesreflectionfordatamappingsoallfieldsinvshouldbeexportedHoweverthiscausesaproblemhowdoesitknowwhichXMLfieldcorrespondstothemappedstructfieldTheansweristhattheXMLparserparsesdatainacertainorderThelibrarywilltrytofindthematchingstructtagfirstIfamatchcannotbefoundthenitsearchesthroughthestructfieldnamesBeawarethatalltagsfieldnamesandXMLelementsarecasesensitivesoyouhavetomakesurethatthereisaone-to-onecorrespondenceforthemappingtosucceed

GosreflectionmechanismallowsyoutousethistaginformationtoreflectXMLdatatoastructobjectIfyouwanttoknowmoreaboutreflectioninGopleasereadthepackagedocumentationonstructtagsandreflection

HerearesomeruleswhenusingthexmlpackagetoparseXMLdocumentstostructs

Ifthefieldtypeisastringor[]bytewiththetaginnerxmlUnmarshalwillassignrawXMLdatatoitlikeDescriptionintheaboveexample

Shanghai_VPN127001Beijing_VPN127002

IfafieldiscalledXMLNameanditstypeisxmlNamethenitgetstheelementnamelikeserversinaboveexample

IfafieldstagcontainsthecorrespondingelementnamethenitgetstheelementnameaswelllikeservernameandserveripintheaboveexampleIfafieldstagcontainsattrthenitgetsthecorrespondingelementsattributelikeversioninaboveexampleIfafieldstagcontainssomethinglikeagtbgtcitgetsthevalueoftheelementcofnodebofnodeaIfafieldstagcontains=thenitgetsnothingIfafieldstagcontainsanythenitgetsallchildelementswhichdonotfittheotherrulesIftheXMLelementshaveoneormorecommentsallofthesecommentswillbeaddedtothefirstfieldthathasthetagthatcontainscommentsThisfieldtypecanbeastringor[]byteIfthiskindoffielddoesnotexistallcommentsarediscarded

TheserulestellyouhowtodefinetagsinstructsOnceyouunderstandtheserulesmappingXMLtostructswillbeaseasyasthesamplecodeaboveBecausetagsandXMLelementshaveaone-to-onecorrespondencewecanalsouseslicestorepresentmultipleelementsonthesamelevel

Notethatallfieldsinstructsshouldbeexported(capitalized)inordertoparsedatacorrectly

ProduceXMLWhatifwewanttoproduceanXMLdocumentinsteadofparsingoneHowdowedothisinGoUnsurprisinglythexmlpackageprovidestwofunctionswhichareMarshalandMarshalIndentwherethesecondfunctionautomaticallyindentsthemarshalledXMLdocumentTheirdefinitionasfollows

funcMarshal(vinterface)([]byteerror)

funcMarshalIndent(vinterfaceprefixindentstring)([]byteerror)

ThefirstargumentinbothofthesefunctionsisforstoringamarshalledXMLdatastream

Letslookatanexampletoseehowthisworks

packagemain

import(

encodingxml

typeServersstruct

typeserverstruct

funcmain()

v=ampServersVersion1

vSvs=append(vSvsserverShanghai_VPN127001)

vSvs=append(vSvsserverBeijing_VPN127002)

outputerr=xmlMarshalIndent(v)

iferr=nil

fmtPrintf(errorvnerr)

osStdoutWrite([]byte(xmlHeader))

osStdoutWrite(output)

Theaboveexampleprintsthefollowinginformation

ltxmlversion=10encoding=UTF-8gt

ltservergt

ltserversgt

AswevepreviouslydefinedthereasonwehaveosStdoutWrite([]byte(xmlHeader))isbecausebothxmlMarshalIndentandxmlMarshaldonotoutputXMLheadersontheirownsowehavetoexplicitlyprinttheminordertoproduceXMLdocumentscorrectly

HerewecanseethatMarshalalsoreceivesavparameteroftypeinterfaceSowhataretheruleswhenmarshallingtoanXMLdocument

IfvisanarrayorsliceitprintsallelementslikeavalueIfvisapointeritprintsthecontentthatvispointingtoprintingnothingwhenvisnilIfvisainterfaceitdealwiththeinterfaceaswellIfvisoneoftheothertypesitprintsthevalueofthattype

SohowdoesxmlMarshaldecidetheelementsnameItfollowstheensuingrules

IfvisastructitdefinesthenameinthetagofXMLNameThefieldnameisXMLNameandthetypeisxmlNameFieldtaginstructFieldnameinstructTypenameofmarshal

ThenweneedtofigureouthowtosettagsinordertoproducethefinalXMLdocument

XMLNamewillnotbeprintedFieldsthathavetagscontaining-willnotbeprintedIfatagcontainsnameattritusesnameastheattributenameandthefieldvalueasthevaluelikeversionintheaboveexampleIfatagcontainsattritusesthefieldsnameastheattributenameandthefieldvalueasitsvalueIfatagcontainschardataitprintscharacterdatainsteadofelementIfatagcontainsinnerxmlitprintstherawvalueIfatagcontainscommentitprintsitasacommentwithoutescapingsoyoucannothave--initsvalueIfatagcontainsomitemptyitomitsthisfieldifitsvalueiszero-valueincludingfalse0nilpointerornilinterfacezerolengthofarrayslicemapandstringIfatagcontainsagtbgtcitprintsthreeelementswhereacontainsbandbcontainsclikeinthefollowingcode `xmlFirstNamestringxmlnamegtfirstLastNamestringxmlnamegtlast`

Xieltnamegt```YoumayhavenoticedthatstructtagsareveryusefulfordealingwithXMLandthesamegoesfortheotherdataformatswellbediscussinginthefollowingsectionsIfyoustillfindthatyouhaveproblemswithworkingwithstructtagsyoushouldprobablyreadmoredocumentationaboutthembeforedivingintothenextsection

LinksDirectoryPrevioussectionTextfilesNextsectionJSON

72JSONJSON(JavaScriptObjectNotation)isalightweightdataexchangelanguagewhichisbasedontextdescriptionItsadvantagesincludebeingself-descriptiveeasytounderstandetcEventhoughitisasubsetofJavaScriptJSONusesadifferenttextformattheresultbeingthatitcanbeconsideredasanindependentlanguageJSONbearssimilaritytoC-familylanguages

ThebiggestdifferencebetweenJSONandXMListhatXMLisacompletemarkuplanguagewhereasJSONisnotJSONissmallerandfasterthanXMLthereforeitsmucheasierandquickertoparseinbrowserswhichisoneofthereasonswhymanyopenplatformschoosetouseJSONastheirdataexchangeinterfacelanguage

SinceJSONisbecomingmoreandmoreimportantinwebdevelopmentletstakealookatthelevelofsupportGohasforJSONYoullfindthatGosstandardlibraryhasverygoodsupportforencodinganddecodingJSON

HereweuseJSONtorepresenttheexampleintheprevioussection

servers[serverNameShanghai_VPNserverIP127001serverNameBeijing_VPNserverIP127002]

TherestofthissectionwillusethisJSONdatatointroduceJSONconceptsinGo

ParseJSON

Parsetostruct

SupposewehavetheJSONintheaboveexampleHowcanweparsethisdataandmapittoastructinGoGoprovidesthefollowingfunctionforjustthispurpose

Wecanusethisfunctionlikeso

packagemain

import(

encodingjson

typeServerstruct

ServerNamestring

ServerIPstring

typeServerslicestruct

Servers[]Server

funcmain()

varsServerslice

str=`servers[serverNameShanghai_VPNserverIP127001serverNameBeijing_VPNserverIP

127002]`

jsonUnmarshal([]byte(str)amps)

fmtPrintln(s)

IntheaboveexamplewedefinedacorrespondingstructsinGoforourJSONusingsliceforanarrayofJSONobjectsandfieldnameasourJSONkeysButhowdoesGoknowwhichJSONobjectcorrespondstowhichspecificstructfiledSupposewehaveakeycalledFooinJSONHowdowefinditscorrespondingfield

FirstGotriestofindthe(capitalised)exportedfieldwhosetagcontainsFooIfnomatchcanbefoundlookforthefieldwhosenameisFooIftherearestillnotmatcheslookforsomethinglikeFOOorFoOignoringcasesensitivity

YoumayhavenoticedthatallfieldsthataregoingtobeassignedshouldbeexportedandGoonlyassignsfieldsthatcanbefoundignoringallothersThiscanbeusefulifyouneedtodealwithlargechunksofJSONdatabutyouonlyaspecificsubsetofitthedatayoudontneedcaneasilybediscarded

ParsetointerfaceWhenweknowwhatkindofJSONtoexpectinadvancewecanparseittoaspecificstructButwhatifwedontknow

WeknowthataninterfacecanbeanythinginGosoitisthebestcontainertosaveourJSONofunknownformatTheJSONpackageusesmap[string]interfaceand[]interfacetosaveallkindsofJSONobjectsandarraysHereisalistofJSONmappingrelations

boolrepresentsJSONbooleansfloat64representsJSONnumbersstringrepresentsJSONstringsnilrepresentsJSONnull

SupposewehavethefollowingJSONdata

b=[]byte(`NameWednesdayAge6Parents[GomezMorticia]`)

NowweparsethisJSONtoaninterface

varfinterface

err=jsonUnmarshal(bampf)

Thefstoresamapwherekeysarestringsandvaluesareinterfaces

f=map[string]interface

NameWednesday

Parents[]interface

Morticia

SohowdoweaccessthisdataTypeassertion

m=f(map[string]interface)

Afterassertedyoucanusethefollowingcodetoaccessdata

forkv=rangem

switchvv=v(type)

casestring

fmtPrintln(kisstringvv)

caseint

fmtPrintln(kisintvv)

casefloat64

fmtPrintln(kisfloat64vv)

case[]interface

fmtPrintln(kisanarray)

foriu=rangevv

fmtPrintln(iu)

default

fmtPrintln(kisofatypeIdontknowhowtohandle)

AsyoucanseewecannowparseJSONofanunknownformatthroughinterfaceandtypeassertion

TheaboveexampleistheofficialsolutionbuttypeassertingisnotalwaysconvenientSoIrecommendanopensourceprojectcalledsimplejsoncreatedandmaintainedbybitlyHereisanexampleofhowtousethisprojecttodealwithJSONofanunknownformat

jserr=NewJson([]byte(`

array[123]

float5150

bignum9223372036854775807

stringsimplejson

booltrue

arr_=jsGet(test)Get(array)Array()

i_=jsGet(test)Get(int)Int()

ms=jsGet(test)Get(string)MustString()

ItsnothardtoseehowconvenientthisisCheckouttherepositorytoseemoreinformationhttpsgithubcombitlygo-simplejson

ProducingJSONInmanysituationsweneedtoproduceJSONdataandrespondtoclientsInGotheJSONpackagehasafunctioncalledMarshaltodojustthat

SupposeweneedtoproduceaserverinformationlistWehavefollowingsample

packagemain

import(

encodingjson

typeServerstruct

ServerNamestring

ServerIPstring

Servers[]Server

funcmain()

varsServerslice

sServers=append(sServersServerServerNameShanghai_VPNServerIP127001)

sServers=append(sServersServerServerNameBeijing_VPNServerIP127002)

berr=jsonMarshal(s)

iferr=nil

fmtPrintln(jsonerrerr)

fmtPrintln(string(b))

Output

Servers[ServerNameShanghai_VPNServerIP127001ServerNameBeijing_VPNServerIP127002]

AsyouknowallfieldnamesarecapitalizedbutifyouwantyourJSONkeynamestostartwithalowercaseletteryoushouldusestructtagsOtherwiseGowillnotproducedataforinternalfields

typeServerstruct

ServerNamestring`jsonserverName`

ServerIPstring`jsonserverIP`

Servers[]Server`jsonservers`

AfterthismodificationwecanproducethesameJSONdataasbefore

HerearesomepointsyouneedtokeepinmindwhentryingtoproduceJSON

Fieldtagscontaining-willnotbeoutputtedIfatagcontainsacustomizednameGousesthisinsteadofthefieldnamelikeserverNameintheaboveexampleIfatagcontainsomitemptythisfieldwillnotbeoutputtedifitiszero-valueIfthefieldtypeisboolstringintint64etcanditstagcontainsstringGoconvertsthisfieldtoitscorrespondingJSONtype

Example

typeServerstruct

IDwillnotbeoutputed

IDint`json-`

ServerName2willbeconvertedtoJSONtype

ServerName2string`jsonserverName2string`

IfServerIPisemptyitwillnotbeoutputted

ServerIPstring`jsonserverIPomitempty`

s=Server

ServerName`Go10`

ServerName2`Go10`

ServerIP``

b_=jsonMarshal(s)

osStdoutWrite(b)

Output

serverNameGo10serverName2Go10

TheMarshalfunctiononlyreturnsdatawhenithassucceededsoherearesomepointsweneedtokeepinmind

JSONonlysupportsstringsaskeyssoifyouwanttoencodeamapitstypehastobemap[string]TwhereTisthetypeinGoTypeslikechannelcomplextypesandfunctionsarenotcapableofbeingencodedtoJSONDonottrytoencodecyclicdataitleadstoaninfiniterecursionIfthefieldisapointerGooutputsthedatathatitpointstoorelseoutputsnullifitpointstonil

InthissectionweintroducedhowtodecodeandencodeJSONdatainGoWealsolookedatonethird-partyprojectcalledsimplejsonwhichisusefulforparsingJSONorunknownformatTheseareallusefulconceptsfordevelopingwebapplicationsinGo

LinksDirectoryPrevioussectionXMLNextsectionRegexp

73RegexpRegularExpressions(Regexp)isacomplicatedbutpowerfultoolforpatternmatchingandtextmanipulationAlthoughitdoesnotperformaswellaspuretextmatchingitsmoreflexibleBasedonitssyntaxyoucanfilteralmostanykindoftextfromyoursourcecontentIfyouneedtocollectdatainwebdevelopmentitsnotdifficulttouseRegexptoretrievemeaningfuldata

GohastheregexppackagewhichprovidesofficialsupportforregexpIfyouvealreadyusedregexpinotherprogramminglanguagesyoushouldbefamiliarwithitNotethatGoimplementedRE2standardexceptforCFormoredetailsfollowthislinkhttpcodegooglecompre2wikiSyntax

Gosstringspackagecanactuallydomanyjobslikesearching(ContainsIndex)replacing(Replace)parsing(SplitJoin)etcanditsfasterthanRegexpHoweverthesearealltrivialoperationsIfyouwanttosearchacaseinsensitivestringRegexpshouldbeyourbestchoiceSoifthestringspackageissufficientforyourneedsjustuseitsinceitseasytouseandreadifyouneedtoperformmoreadvancedoperationsuseRegexp

IfyourecallformvalidationfromprevioussectionsweusedRegexptoverifythevalidityofuserinputinformationBeawarethatallcharactersareUTF-8LetslearnmoreabouttheGoregexppackage

MatchTheregexppackagehas3functionstomatchifitmatchesapatternthenitreturnstruereturningfalseotherwise

funcMatch(patternstringb[]byte)(matchedboolerrorerror)

funcMatchReader(patternstringrioRuneReader)(matchedboolerrorerror)

funcMatchString(patternstringsstring)(matchedboolerrorerror)

All3functionscheckifpatternmatchestheinputsourcereturningtrueifitmatchesHoweverifyourRegexhassyntaxerrorsitwillreturnanerrorThe3inputsourcesofthesefunctionsaresliceofbyteRuneReaderandstring

HereisanexampleofhowtoverifyanIPaddress

funcIsIP(ipstring)(bbool)

ifm_=regexpMatchString(^[0-9]13[0-9]13[0-9]13[0-9]13$ip)m

returnfalse

returntrue

AsyoucanseeusingpatternintheregexppackageisnotthatdifferentHeresonemoreexampleonverifyingwhetheruserinputisvalid

funcmain()

iflen(osArgs)==1

fmtPrintln(Usageregexp[string])

osExit(1)

elseifm_=regexpMatchString(^[0-9]+$osArgs[1])m

fmtPrintln(Number)

fmtPrintln(Notnumber)

IntheaboveexamplesweuseMatch(Reader|String)tocheckifcontentisvalidbuttheyarealleasytouse

Regexp

FilterMatchmodecanverifycontentbutitcannotcutfilterorcollectdatafromitIfyouwanttodothatyouhavetousethecomplexmodeofRegexp

LetssayweneedtowriteacrawlerHereisanexampleforwhenyoumustuseRegexptofilterandcutdata

packagemain

import(

ioioutil

nethttp

regexp

strings

funcmain()

resperr=httpGet(httpwwwbaiducom)

iferr=nil

fmtPrintln(httpgeterror)

bodyerr=ioutilReadAll(respBody)

iferr=nil

fmtPrintln(httpreaderror)

return

src=string(body)

ConvertHTMLtagstolowercase

re_=regexpCompile(lt[Ss]+gt)

src=reReplaceAllStringFunc(srcstringsToLower)

RemoveSTYLE

re_=regexpCompile(ltstyle[Ss]+ltstylegt)

src=reReplaceAllString(src)

RemoveSCRIPT

re_=regexpCompile(ltscript[Ss]+ltscriptgt)

RemoveallHTMLcodeinanglebracketsandreplacewithnewline

src=reReplaceAllString(srcn)

Removecontinuousnewline

re_=regexpCompile(s2)

fmtPrintln(stringsTrimSpace(src))

InthisexampleweuseCompileasthefirststepforcomplexmodeItverifiesthatyourRegexsyntaxiscorrectthenreturnsaRegexpforparsingcontentinotheroperations

HerearesomefunctionstoparseyourRegexpsyntax

funcCompile(exprstring)(Regexperror)

funcCompilePOSIX(exprstring)(Regexperror)

funcMustCompile(strstring)Regexp

funcMustCompilePOSIX(strstring)Regexp

Regexp

ThedifferencebetweenComplePOSIXandCompileisthattheformerhastousePOSIXsyntaxwhichisleftmostlongestsearchandthelatterisonlyleftmostsearchForinstanceforRegexp[a-z]24andcontentaa09aaa88aaaaCompilePOSIXreturnsaaaabutCompilereturnsaaMustprefixmeanspanicwhentheRegexpsyntaxisnotcorrectreturningerrorotherwise

NowthatweknowhowtocreateanewRegexpletsseehowthemethodsprovidedbythisstructcanhelpustooperateoncontent

func(reRegexp)Find(b[]byte)[]byte

func(reRegexp)FindAll(b[]bytenint)[][]byte

func(reRegexp)FindAllIndex(b[]bytenint)[][]int

func(reRegexp)FindAllString(sstringnint)[]string

func(reRegexp)FindAllStringIndex(sstringnint)[][]int

func(reRegexp)FindAllStringSubmatch(sstringnint)[][]string

func(reRegexp)FindAllStringSubmatchIndex(sstringnint)[][]int

func(reRegexp)FindAllSubmatch(b[]bytenint)[][][]byte

func(reRegexp)FindAllSubmatchIndex(b[]bytenint)[][]int

func(reRegexp)FindIndex(b[]byte)(loc[]int)

func(reRegexp)FindReaderIndex(rioRuneReader)(loc[]int)

func(reRegexp)FindReaderSubmatchIndex(rioRuneReader)[]int

func(reRegexp)FindString(sstring)string

func(reRegexp)FindStringIndex(sstring)(loc[]int)

func(reRegexp)FindStringSubmatch(sstring)[]string

func(reRegexp)FindStringSubmatchIndex(sstring)[]int

func(reRegexp)FindSubmatch(b[]byte)[][]byte

func(reRegexp)FindSubmatchIndex(b[]byte)[]int

These18methodsincludeidenticalfunctionsfordifferentinputsources(byteslicestringandioRuneReader)sowecanreallysimplifythislistbyignoringinputsourcesasfollows

Codesample

Regexp

packagemain

import(

regexp

funcmain()

a=IamlearningGolanguage

re_=regexpCompile([a-z]24)

Findthefirstmatch

one=reFind([]byte(a))

fmtPrintln(Findstring(one))

Findallmatchesandsavetoaslicenlessthan0meansreturnallmatchesindicateslengthofsliceifit

sgreaterthan0

all=reFindAll([]byte(a)-1)

fmtPrintln(FindAllall)

Findindexoffirstmatchstartandendposition

index=reFindIndex([]byte(a))

fmtPrintln(FindIndexindex)

Findindexofallmatchesthendoessamejobasabove

allindex=reFindAllIndex([]byte(a)-1)

fmtPrintln(FindAllIndexallindex)

re2_=regexpCompile(am()lang())

Findfirstsubmatchandreturnarraythefirstelementcontainsallelementsthesecondelementcontainsthe

resultoffirst()thethirdelementcontainstheresultofsecond()

Output

thefirstelementamlearningGolanguage

thesecondelementlearningGonoticespaceswillbeoutputedaswell

thethirdelementuage

submatch=re2FindSubmatch([]byte(a))

fmtPrintln(FindSubmatchsubmatch)

for_v=rangesubmatch

fmtPrintln(string(v))

SameasFindIndex()

submatchindex=re2FindSubmatchIndex([]byte(a))

fmtPrintln(submatchindex)

FindAllSubmatchfindallsubmatches

submatchall=re2FindAllSubmatch([]byte(a)-1)

fmtPrintln(submatchall)

FindAllSubmatchIndexfindindexofallsubmatches

submatchallindex=re2FindAllSubmatchIndex([]byte(a)-1)

fmtPrintln(submatchallindex)

AswevepreviouslymentionedRegexpalsohas3methodsformatchingTheydotheexactsamethingastheexportedfunctionsInfactthoseexportedfunctionsactuallycallthesemethodsunderthehood

func(reRegexp)Match(b[]byte)bool

func(reRegexp)MatchReader(rioRuneReader)bool

func(reRegexp)MatchString(sstring)bool

NextletsseehowtoreplacestringsusingRegexp

Regexp

func(reRegexp)ReplaceAll(srcrepl[]byte)[]byte

func(reRegexp)ReplaceAllFunc(src[]bytereplfunc([]byte)[]byte)[]byte

func(reRegexp)ReplaceAllLiteral(srcrepl[]byte)[]byte

func(reRegexp)ReplaceAllLiteralString(srcreplstring)string

func(reRegexp)ReplaceAllString(srcreplstring)string

func(reRegexp)ReplaceAllStringFunc(srcstringreplfunc(string)string)string

Theseareusedinthecrawlingexamplesowewillnotexplainanyfurtherhere

LetstakealookatthedefinitionofExpand

func(reRegexp)Expand(dst[]bytetemplate[]bytesrc[]bytematch[]int)[]byte

func(reRegexp)ExpandString(dst[]bytetemplatestringsrcstringmatch[]int)[]byte

SohowdoweuseExpand

funcmain()

src=[]byte(`

callhelloalice

hellobob

callhelloeve

pat=regexpMustCompile(`(m)(call)s+(Pltcmdgtw+)s+(Pltarggt+)s$`)

res=[]byte

for_s=rangepatFindAllSubmatchIndex(src-1)

res=patExpand(res[]byte($cmd($arg)n)srcs)

fmtPrintln(string(res))

AtthispointyouvelearntthewholeregexppackageinGoIhopethatyoucanunderstandmorebystudyingexamplesofkeymethodssothatyoucandosomethinginterestingonyourown

LinksDirectoryPrevioussectionJSONNextsectionTemplates

Regexp

74Templates

WhatisatemplateHopefullyyoureawareoftheMVC(ModelViewController)designmodelwheremodelsprocessdataviewsshowtheresultsandfinallycontrollershandleuserrequestsForviewsmanydynamiclanguagesgeneratedatabywritingcodeinstaticHTMLfilesForinstanceJSPisimplementedbyinsertinglt==gtPHPbyinsertingltphpgtetc

Thefollowingdemonstratesthetemplatemechanism

Figure71Templatemechanism

MostofthecontentthatwebapplicationsrespondtoclientswithisstaticandthedynamicpartsareusuallyverysmallForexampleifyouneedtodisplayalistuserswhohavevisitedapageonlytheusernamewouldbedynamicThestyleofthelistremainsthesameAsyoucanseetemplatesareusefulforreusingstaticcontent

TemplatinginGoInGowehavethetemplatepackagetohelphandletemplatesWecanusefunctionslikeParseParseFileandExecutetoloadtemplatesfromplaintextorfilesthenevaluatethedynamicpartsasshowninfigure71

Example

funchandler(whttpResponseWriterrhttpRequest)

t=templateNew(sometemplate)Createatemplate

t_=tParseFiles(tmplwelcomehtmlnil)Parsetemplatefile

user=GetUser()Getcurrentuserinfomration

tExecute(wuser)merge

AsyoucanseeitsveryeasytouseloadandrenderdataintemplatesinGojustasinotherprogramminglanguages

Forthesakeofconveniencewewillusethefollowingrulesinourexamples

UseParsetoreplaceParseFilesbecauseParsecantestcontentdirectlyfromstringssowedontneedanyextrafilesUsemainforeveryexampleanddonotusehandlerUseosStdouttoreplacehttpResponseWritersinceosStdoutalsoimplementstheioWriterinterface

InsertingdataintoatemplateWevejustshownyouhowtoparseandrendertemplatesLetstakeitonestepfurtherandrenderdatatoourtemplatesEverytemplateisanobjectinGosohowdoweinsertfieldstotemplates

Fields

InGoEveryfieldthatyouintendtoberenderedwithinatemplateshouldbeputinsideofisshorthandforthecurrentobjectwhichissimilartoitsJavaorC++counterpartIfyouwanttoaccessthefieldsofthecurrentobjectyoushoulduseFieldNameNoticethatonlyexportedfieldscanbeaccessedintemplatesHereisanexample

Templates

packagemain

import(

htmltemplate

typePersonstruct

UserNamestring

funcmain()

t=templateNew(fieldnameexample)

t_=tParse(helloUserName)

p=PersonUserNameAstaxie

tExecute(osStdoutp)

TheaboveexampleoutputshelloAstaxiecorrectlybutifwemodifyourstructalittlebitthefollowingerroremerges

typePersonstruct

UserNamestring

emailstringFieldisnotexported

t_=tParse(helloUserNameemail)

ThispartofthecodewillnotbecompiledbecausewetrytoaccessafieldthathasnotbeenexportedHoweverifwetrytouseafieldthatdoesnotexistGosimplyoutputsanemptystringinsteadofanerror

IfyouprintinatemplateGooutputsaformattedstringofthisobjectcallingfmtunderthecovers

Nestedfields

WeknowhowtooutputafieldnowWhatifthefieldisanobjectanditalsohasitsownfieldsHowdoweprintthemallinoneloopWecanusewithhelliphellipendandrangehellipendforexactlythatpurpose

rangejustlikerangeinGowithletsyouwritethesameobjectnameonceanduseasshorthandforit(SimilartowithinVB)

Moreexamples

Templates

packagemain

import(

htmltemplate

typeFriendstruct

Fnamestring

typePersonstruct

UserNamestring

Emails[]string

Friends[]Friend

funcmain()

f1=FriendFnameminuxma

f2=FriendFnamexushiwei

t_=tParse(`helloUserName

rangeEmails

anemail

withFriends

myfriendnameisFname

Emails[]stringastaxiebeegomeastaxiegmailcom

Friends[]Friendampf1ampf2

tExecute(osStdoutp)

ConditionsIfyouneedtocheckforconditionsintemplatesyoucanusetheif-elsesyntaxjustlikeyoudoinregularGoprogramsIfthepipelineisemptythedefaultvalueofifisfalseThefollowingexampleshowshowtouseif-elseintemplates

packagemain

import(

texttemplate

funcmain()

tEmpty=templateNew(templatetest)

tEmpty=templateMust(tEmptyParse(Emptypipelineifdemoif``willnotbeoutputtedendn))

tEmptyExecute(osStdoutnil)

tWithValue=templateNew(templatetest)

tWithValue=templateMust(tWithValueParse(Notemptypipelineifdemoif`anything`willbeoutputtede

tWithValueExecute(osStdoutnil)

tIfElse=templateNew(templatetest)

tIfElse=templateMust(tIfElseParse(if-elsedemoif`anything`ifpartelseelsepartendn))

tIfElseExecute(osStdoutnil)

Asyoucanseeitseasytouseif-elseintemplates

Templates

AttentionYouCANNOTuseconditionalexpressionsinifforinstanceMail==astaxiegmailcomOnlybooleanvaluesareacceptable

pipelines

Unixusersshouldbefamiliarwiththepipeoperatorlikels|grepbeegoThiscommandfiltersfilesandonlyshowsthosethatcontainthewordbeegoOnethingthatIlikeaboutGotemplatesisthattheysupportpipesAnythingincanbethedataofpipelinesThee-mailweusedabovecanrenderourapplicationvulnerabletoXSSattacksHowcanweaddressthisissueusingpipes

Wecanusethismethodtoescapethee-mailbodytoHTMLItsquitesimilartowritingaUnixcommandanditisconvenientforuseintemplatefunctions

TemplatevariablesSometimesweneedtouselocalvariablesintemplatesWecanusethemwiththewithrangeandifkeywordsandtheirscopeisbetweenthesekeywordsandendHeresanexampleofdeclaringaglobalvariable

$variable=pipeline

Moreexamples

with$x=output|printfq$xend

with$x=outputprintfq$xend

with$x=output$x|printfqend

Templatefunctions

GousesthefmtpackagetoformatoutputintemplatesbutsometimesweneedtodosomethingelseForexampleconsiderthefollowingscenarioletssaywewanttoreplacewithatinoure-mailaddresslikeastaxieatbeegomeAtthispointwehavetowriteacustomizedfunction

EverytemplatefunctionhasauniquenameandisassociatedwithonefunctioninyourGoprogramasfollows

typeFuncMapmap[string]interface

SupposewehaveanemailDealtemplatefunctionassociatedwithitsEmailDealWithcounterpartfunctioninourGoprogramWecanusethefollowingcodetoregisterthisfunction

t=tFuncs(templateFuncMapemailDealEmailDealWith)

EmailDealWithdefinition

funcEmailDealWith(argshellipinterface)string

Example

Templates

packagemain

import(

htmltemplate

strings

typeFriendstruct

Fnamestring

typePersonstruct

UserNamestring

Emails[]string

Friends[]Friend

funcEmailDealWith(argsinterface)string

ok=false

varsstring

iflen(args)==1

sok=args[0](string)

s=fmtSprint(args)

findthesymbol

substrs=stringsSplit(s)

iflen(substrs)=2

returns

replacethebyat

return(substrs[0]+at+substrs[1])

funcmain()

rangeEmails

anemails|emailDeal

withFriends

myfriendnameisFname

tExecute(osStdoutp)

Hereisalistofbuilt-intemplatefunctions

Templates

varbuiltins=FuncMap

andand

callcall

htmlHTMLEscaper

indexindex

jsJSEscaper

lenlength

notnot

printfmtSprint

printffmtSprintf

printlnfmtSprintln

urlqueryURLQueryEscaper

MustThetemplatepackagehasafunctioncalledMustwhichisforvalidatingtemplateslikethematchingofbracescommentsandvariablesLetstakealookatanexampleofMust

packagemain

import(

texttemplate

funcmain()

tOk=templateNew(first)

templateMust(tOkParse(somestatictextandacomment))

fmtPrintln(ThefirstoneparsedOK)

templateMust(templateNew(second)Parse(somestatictextName))

fmtPrintln(ThesecondoneparsedOK)

fmtPrintln(Thenextoneoughttofail)

tErr=templateNew(checkparseerrorwithMust)

templateMust(tErrParse(somestatictextName))

Output

ThefirstoneparsedOK

ThesecondoneparsedOK

Thenextoneoughttofail

panictemplatecheckparseerrorwithMust1unexpectedincommand

NestedtemplatesJustlikeinmostwebapplicationscertainpartsoftemplatescanbereusedacrossothertemplatesliketheheadersandfootersofablogWecandeclareheadercontentandfooterassub-templatesanddeclaretheminGousingthefollowingsyntax

definesub-templatecontentend

Thesub-templateiscalledusingthefollowingsyntax

templatesub-template

Templates

Heresacompleteexamplesupposingthatwehavethefollowingthreefilesheadertmplcontenttmplandfootertmplinthefoldertemplateswewillreadthefolderandstorethefilenamesinastringarraywhichwewillthenusetoparsefiles

Maintemplate

headertmpl

defineheader

lthtmlgt

ltheadgt

lttitlegtSomethingherelttitlegt

ltheadgt

ltbodygt

contenttmpl

definecontent

templateheader

lth1gtNestedherelth1gt

ltulgt

ltligtNestedusagltligt

ltligtCalltemplateltligt

ltulgt

templatefooter

footertmpl

definefooter

ltbodygt

lthtmlgt

Whenusingsubtemplatingmakesurethatyouhaveparsedeachsubtemplatefile

otherwisethecompilerwouldntunderstandwhattosubstitutewhenitreadsthetemplateheader

endraw

Templates

packagemain

import(

ioioutil

texttemplate

vartemplatestemplateTemplate

funcmain()

varallFiles[]string

fileserr=ioutilReadDir(templates)

iferr=nil

fmtPrintln(err)

for_file=rangefiles

filename=fileName()

ifstringsHasSuffix(filenametmpl)

allFiles=append(allFilestemplates+filename)

templateserr=templateParseFiles(allFiles)parsesalltmplfilesinthetemplatesfolder

s1=templatesLookup(headertmpl)

s1ExecuteTemplate(osStdoutheadernil)

fmtPrintln()

s2=templatesLookup(contenttmpl)

s2ExecuteTemplate(osStdoutcontentnil)

fmtPrintln()

s3=templatesLookup(footertmpl)

s3ExecuteTemplate(osStdoutfooternil)

fmtPrintln()

s3Execute(osStdoutnil)

HerewecanseethattemplateParseFilesparsesallnestedtemplatesintocacheandthateverytemplatedefinedbydefineareindependentofeachotherTheyarepersistedinsomethinglikeamapwherethetemplatenamesarekeysandthevaluesarethetemplatebodiesWecanthenuseExecuteTemplatetoexecutethecorrespondingsub-templatessothattheheaderandfooterareindependentandcontentcontainsthembothNotethatifwetrytoexecutes1Executenothingwillbeoutputtedbecausethereisnodefaultsub-templateavailable

Whenyoudontwanttousedefinethenyoucanjustcreateatextfilewiththenameofthesubtemplateforinstance_headtmplisasubtemplatewhichyoulluseacrossyourprojectthencreatethisfileinthetemplatesfolderandusethenormalsyntaxLookupcacheisbasicallycreatedsothatyoudontreadthefileeverytimeyouservearequestbecauseifyoudothenyouarewastingalotofresourcesforreadingafilewhichwontchangeunlessthecodebaseisbeingrewrittenitdoesntmakesensetoparsethetemplatefilesduringeachHTTPGETrequestsothetechniqueisusedwhereweparsethefilesonceandthendoaLookup()onthecachetoexecutethetemplatewhenweneedittodisplaydata

Templatesinonesetknoweachotherbutyoumustparsethemforeverysingleset

Sometimesyouwanttocontextualizetemplatesforinstanceyouhavea_headhtmlyoumighthaveaheaderwhosvalueyouhavetopopulatebasedonwhichdatayouareloadingforinstanceforatodolistmanageryoucanhavethreecategoriespendingcompleteddeletedforthissupposeyouhaveanifstatementlikethis

lttitlegtifeqNavigationpendingTasks

elseifeqNavigationcompletedCompleted

elseifeqNavigationdeletedDeleted

elseifeqNavigationeditEdit

lttitlegt

Templates

NoteGotemplatesfollowthePolishnotationwhileperformingthecomparisonwhereyougivetheoperatorfirstandthecomparisonvalueandthevaluetobecomparedwithTheelseifpartisprettystraightforward

Typicallyweusearangeoperatortoloopthroughthecontextvariablewhichwepasstothetemplatewhileexecutionlikethis

presentinviewspackage

context=dbGetTasks(pending)truewhenyouwantnondeletednotes

Wegetthecontextobjectfromthedatabaseasastructobjectthedefinitionisasbelow

Taskisthestructusedtoidentifytasks

typeTaskstruct

Titlestring

Contentstring

Createdstring

Contextisthestructpassedtotemplates

typeContextstruct

Tasks[]Task

Navigationstring

Searchstring

Messagestring

presentindatabasepackage

vartask[]typesTask

varcontexttypesContext

context=typesContextTaskstaskNavigationstatus

Thislineisinthedatabasepackagewherethecontextisreturnedbacktotheview

WeusethetaskarrayandtheNavigationinourtemplateswesawhowweusetheNavigationinthetemplatewellseehowwellusetheactualtaskarrayinourtemplate

HereintheifTaskswefirstcheckiftheTasksfieldofourcontextobjectwhichwepassedtothetemplatewhileexecutingisemptyornotIfitisnotemptythenwewillrangethroughthatarraytopopulatethetitleandcontentofTaskThebelowexampleisveryimportantwhenitcomestoloopingthroughanarrayinatemplatewestartwiththeRangeoperatorthenwecangiveanymemberofthatstructasNamemyTaskstructurehasaTitleandaContent(pleasenotethecapitalTandCtheyareexportednamesandtheyneedtobecapitalisedunlessyouwanttomakethemprivate)

rangeTasks

Content

ThisblockofcodewillprinteachtitleandcontentoftheTaskarrayBelowisafullexamplefromgithubcomthewhitetulipTaskshomehtmltemplate

Templates

ltdivclass=timelinegt

ifTasksrangeTasks

ltdivclass=notegt

ltpclass=noteHeadinggtTitleltpgt

lthrgt

ltpclass=noteContentgtContentltpgt

ltulgt

ltspangt

ltdivgt

endelse

ltdivclass=notegt

ltpclass=noteHeadinggtNoTaskshereltpgt

ltpclass=notefootergt

Createnewtaskltbuttonclass=floating-action-icon-addgthereltbuttongtltpgt

ltdivgt

SummaryInthissectionyoulearnedhowtocombinedynamicdatawithtemplatesusingtechniquesincludingprintingdatainloopstemplatefunctionsandnestedtemplatesBylearningabouttemplateswecanconcludediscussingtheV(View)partoftheMVCarchitectureInthefollowingchapterswewillcovertheM(Model)andC(Controller)aspectsofMVC

LinksDirectoryPrevioussectionRegexpNextsectionFiles

Templates

75FilesFilesareessentialobjectsoneverysinglecomputerdeviceItwontcomeasanysurprisetoyouthatwebapplicationsalsomakeheavyuseofthemInthissectionweregoingtolearnhowtooperateonfilesinGo

DirectoriesInGomostofthefileoperationfunctionsarelocatedintheospackageHerearesomedirectoryfunctions

funcMkdir(namestringpermFileMode)error

Createadirectorywithnamepermisthedirectorypermissionsie0777

funcMkdirAll(pathstringpermFileMode)error

Createmultipledirectoriesaccordingtopathlikeastaxietest1test2

funcRemove(namestring)error

RemovesdirectorywithnameReturnserrorifitsnotadirectoryornotempty

funcRemoveAll(pathstring)error

RemovesmultipledirectoriesaccordingtopathDirectorieswillnotbedeletedifpathisasinglepath

Codesample

packagemain

import(

funcmain()

osMkdir(astaxie0777)

osMkdirAll(astaxietest1test20777)

err=osRemove(astaxie)

iferr=nil

fmtPrintln(err)

osRemoveAll(astaxie)

Createandopenfiles

Therearetwofunctionsforcreatingfiles

funcCreate(namestring)(fileFileerrError)

Createafilewithnameandreturnaread-writablefileobjectwithpermission0666

funcNewFile(fduintptrnamestring)File

Createafileandreturnafileobject

Therearealsotwofunctionstoopenfiles

funcOpen(namestring)(fileFileerrError)

Opensafilecallednamewithread-onlyaccesscallingOpenFileunderthecovers

funcOpenFile(namestringflagintpermuint32)(fileFileerrError)

Opensafilecallednameflagisopenmodelikeread-onlyread-writeetcpermarethefilepermissions

WritefilesFunctionsforwritingfiles

func(fileFile)Write(b[]byte)(ninterrError)

Writebytetypecontenttoafile

func(fileFile)WriteAt(b[]byteoffint64)(ninterrError)

Writebytetypecontenttoaspecificpositionofafile

func(fileFile)WriteString(sstring)(retinterrError)

Writeastringtoafile

Codesample

packagemain

import(

funcmain()

userFile=astaxietxt

fouterr=osCreate(userFile)

iferr=nil

fmtPrintln(userFileerr)

return

deferfoutClose()

fori=0ilt10i++

foutWriteString(Justatestrn)

foutWrite([]byte(Justatestrn))

ReadfilesFunctionsforreadingfiles

func(fileFile)Read(b[]byte)(ninterrError)

Readdatatob

func(fileFile)ReadAt(b[]byteoffint64)(ninterrError)

Readdatafrompositionofftob

Codesample

packagemain

import(

funcmain()

userFile=asatxietxt

flerr=osOpen(userFile)

iferr=nil

return

deferflClose()

buf=make([]byte1024)

n_=flRead(buf)

if0==n

osStdoutWrite(buf[n])

DeletefilesGousesthesamefunctionforremovingfilesanddirectories

funcRemove(namestring)Error

Removeafileordirectorycalledname(anameendingwithsignifiesthatitsadirectory)

LinksDirectoryPrevioussectionTemplatesNextsectionStrings

76StringsOnthewebalmosteverythingwesee(includinguserinputsdatabaseaccessetc)isrepresentedbystringsTheyareaveryimportantpartofwebdevelopmentInmanycaseswealsoneedtosplitjoinconvertandotherwisemanipulatestringsInthissectionwearegoingtointroducethestringsandstrconvpackagesfromtheGostandardlibrary

stringsThefollowingfunctionsarefromthestringspackageSeetheofficialdocumentationformoredetails

funcContains(ssubstrstring)bool

Checkifstringscontainsstringsubstrreturnsabooleanvalue```GofmtPrintln(stringsContains(seafoodfoo))fmtPrintln(stringsContains(seafoodbar))fmtPrintln(stringsContains(seafood))fmtPrintln(stringsContains())

Outputtruefalsetruetrue

-funcJoin(a[]stringsepstring)string

Combinestringsfromslicewithseparator`sep`

s=[]stringfoobarbaz

fmtPrintln(stringsJoin(s))

Outputfoobarbaz

funcIndex(ssepstring)int

Findindexofsepinstringsreturns-1ifitsnotfound

fmtPrintln(stringsIndex(chickenken))

fmtPrintln(stringsIndex(chickendmr))

Output4

funcRepeat(sstringcountint)string

Repeatstringscounttimes

fmtPrintln(ba+stringsRepeat(na2))

Outputbanana

funcReplace(soldnewstringnint)string

ReplacestringoldwithstringnewinstringsnisthenumberofreplacementsIfnislessthan0replaceallinstances

fmtPrintln(stringsReplace(oinkoinkoinkkky2))

fmtPrintln(stringsReplace(oinkoinkoinkoinkmoo-1))

Outputoinkyoinkyoink

moomoomoo

funcSplit(ssepstring)[]string

Splitstringswithseparatorsepintoaslice

Strings

fmtPrintf(qnstringsSplit(abc))

fmtPrintf(qnstringsSplit(amanaplanacanalpanamaa))

fmtPrintf(qnstringsSplit(xyz))

fmtPrintf(qnstringsSplit(BernardoOHiggins))

Output[abc]

[manplancanalpanama]

funcTrim(sstringcutsetstring)string

Removecutsetofstringsifitsleftmostorrightmost

fmtPrintf([q]stringsTrim(Achtung))

Output[Achtung]

funcFields(sstring)[]string

Removespaceitemsandsplitstringwithspaceintoaslice

fmtPrintf(FieldsareqstringsFields(foobarbaz))

OutputFieldsare[foobarbaz]

strconvThefollowingfunctionsarefromthestrconvpackageAsusualpleaseseeofficialdocumentationformoredetails

Appendseriesconvertdatatostringandappendtocurrentbyteslice```Gopackagemain

import(fmtstrconv)

funcmain()str=make([]byte0100)str=strconvAppendInt(str456710)str=strconvAppendBool(strfalse)str=strconvAppendQuote(strabcdefg)str=strconvAppendQuoteRune(str单)fmtPrintln(string(str))

-Formatseriesconvertotherdatatypesintostring

packagemain

import(

strconv

funcmain()

a=strconvFormatBool(false)

b=strconvFormatFloat(12323g1264)

c=strconvFormatInt(123410)

d=strconvFormatUint(1234510)

e=strconvItoa(1023)

fmtPrintln(abcde)

Parseseriesconvertstringstoothertypes```Gopackagemain

import(fmtstrconv)

funcmain()aerr=strconvParseBool(false)iferr=nilfmtPrintln(err)berr=strconvParseFloat(1232364)iferr=nilfmtPrintln(err)cerr=strconvParseInt(12341064)iferr=nilfmtPrintln(err)derr=strconvParseUint(123451064)iferr=nilfmtPrintln(err)eerr=strconvItoa(1023)iferr=nilfmtPrintln(err)fmtPrintln(abcde)```

Strings

LinksDirectoryPrevioussectionFilesNextsectionSummary

Strings

77SummaryInthischapterweintroducedsometextprocessingtoolslikeXMLJSONRegexpandwealsotalkedabouttemplatesXMLandJSONaredataexchangetoolsYoucanrepresentalmostanykindofinformationusingthesetwoformatsRegexpisapowerfultoolforsearchingreplacingandcuttingtextcontentWithtemplatesyoucaneasilycombinedynamicdatawithstaticfilesThesetoolsareallusefulwhendevelopingwebapplicationsIhopethatyounowhaveabetterunderstandingofprocessinganddisplayingcontentusingGo

LinksDirectoryPrevioussectionStringsNextchapterWebservices

Summary

8WebservicesWebservicesallowyouuseformatslikeXMLorJSONtoexchangeinformationthroughHTTPForexampleifyouwanttoknowtheweatherinShanghaitomorrowthecurrentsharepriceofAppleorproductinformationonAmazonyoucanwriteapieceofcodetofetchthatinformationfromopenplatformsInGothisprocesscanbecomparabletocallingalocalfunctionandgettingitsreturnvalue

ThekeypointisthatwebservicesareplatformindependentThisallowsyoutodeployyourapplicationsonLinuxandinteractwithASPNETapplicationsinWindowsforexamplejustlikeyouwouldnthaveaprobleminteractingwithJSPonFreeBSDeither

TheRESTarchitectureandSOAPprotocolarethemostpopularstylesinwhichwebservicescanbeimplementedthesedays

RESTrequestsareprettystraightforwardbecauseitsbasedonHTTPEveryRESTrequestisactuallyanHTTPrequestandservershandlerequestsusingdifferentmethodsBecausemanydevelopersarefamiliarwithHTTPalreadyRESTshouldfeellikeitsalreadyintheirbackpocketsWearegoingtoshowyouhowtoimplementRESTinGoinsection83SOAPisastandardforcross-networkinformationtransmissionandremotecomputerfunctioncallslaunchedbyW3CTheproblemwithSOAPisthatitsspecificationisverylongandcomplicatedanditsstillgettinglongerGobelievesthatthingsshouldbesimplesowerenotgoingtotalkaboutSOAPFortunatelyGoprovidessupportforRPC(RemoteProcedureCalls)whichhasgoodperformanceandiseasytodevelopwithsowewillintroducehowtoimplementRPCinGoinsection84

GoistheClanguageofthe21stcenturyaspiringtobesimpleyetperformantWiththesequalitiesinmindwellintroduceyoutosocketprogramminginGoinsection81Nowadaysmanyreal-timeserversusesocketstoovercomethelowperformanceofHTTPAlongwiththerapiddevelopmentofHTML5websocketsarenowusedbymanywebbasedgamecompaniesandwewilltalkaboutthismoreinsection82

LinksDirectoryPreviousChapterChapter7SummaryNextsectionSockets

Webservices

81SocketsSomenetworkapplicationdeveloperssaythatthelowerapplicationlayersareallaboutsocketprogrammingThismaynotbetrueforallcasesbutmanymodernwebapplicationsdoindeedusesocketstotheiradvantageHaveyoueverwonderedhowbrowserscommunicatewithwebserverswhenyouaresurfingtheinternetOrHowMSNconnectsyouandyourfriendstogetherinachatroomrelayingeachmessageinreal-timeManyservicesliketheseusesocketstotransferdataAsyoucanseesocketsoccupyanimportantpositioninnetworkprogrammingtodayandweregoingtolearnaboutusingsocketsinGointhissection

WhatisasocketSocketsoriginatefromUnixandgiventhebasiceverythingisafilephilosophyofUnixeverythingcanbeoperatedonwithopen-gtwriteread-gtcloseSocketsareoneimplementationofthisphilosophySocketshaveafunctioncallforopeningasocketjustlikeyouwouldopenafileThisreturnsanintdescriptorofthesocketwhichcanthenbeusedforoperationslikecreatingconnectionstransferringdataetc

Twotypesofsocketsthatarecommonlyusedarestreamsockets(SOCK_STREAM)anddatagramsockets(SOCK_DGRAM)Streamsocketsareconnection-orientedlikeTCPwhiledatagramsocketsdonotestablishconnectionslikeUDP

SocketcommunicationBeforeweunderstandhowsocketscommunicatewithoneanotherweneedtofigureouthowtomakesurethateverysocketisuniqueotherwiseestablishingareliablecommunicationchannelisalreadyoutofthequestionWecangiveeveryprocessauniquePIDwhichservesourpurposelocallyhoweverthatsnotabletoworkoveranetworkFortunatelyTCPIPhelpsussolvethisproblemTheIPaddressesofthenetworklayerareuniqueinanetworkofhostsandprotocol+portisalsouniqueamonghostapplicationsSowecanusetheseprinciplestomakesocketswhichareunique

Figure81networkprotocollayers

ApplicationsthatarebasedonTCPIPallusesocketAPIsintheircodeinonewayoranotherGiventhatnetworkedapplicationsarebecomingmoreandmoreprevalentinthemoderndayitsnowondersomedevelopersaresayingthateverythingisaboutsockets

SocketbasicknowledgeWeknowthatsocketshavetwotypeswhichareTCPsocketsandUDPsocketsTCPandUDPareprotocolsandasmentionedwealsoneedanIPaddressandportnumbertohaveauniquesocket

IPv4TheglobalinternetusesTCPIPasitsprotocolwhereIPisthenetworklayerandacorepartofTCPIPIPv4signifiesthatitsversionis4infrastructuredevelopmenttodatehasspannedover30years

ThenumberofbitsinanIPv4addressis32whichmeansthat2^32devicesareabletouniquelyconnecttotheinternetDuetotherapiddevelopoftheinternetIPaddressesarealreadyrunningoutofstockinrecentyears

Addressformat127001172122121111

Sockets

IPv6isthenextversionornextgenerationoftheinternetItsbeingdevelopedforsolvingmanyoftheproblemsinherentwithIPv4DevicesusingIPv6haveanaddressthats128bitslongsowellneverneedtoworryaboutashortageofuniqueaddressesToputthisintoperspectiveyoucouldhavemorethan1000IPaddressesforeverysquaremeteronearthwithIPv6Otherproblemslikepeertopeerconnectionservicequality(QoS)securitymultiplebroadcastetcarealsobeimproved

Addressformat2002c0e882e7000c0e882e7

IPtypesinGo

ThenetpackageinGoprovidesmanytypesfunctionsandmethodsfornetworkprogrammingThedefinitionofIPasfollows

typeIP[]byte

FunctionParseIP(sstring)IPistoconverttheIPv4orIPv6formattoanIP

packagemain

import(

funcmain()

iflen(osArgs)=2

fmtFprintf(osStderrUsagesip-addrnosArgs[0])

osExit(1)

name=osArgs[1]

addr=netParseIP(name)

ifaddr==nil

fmtPrintln(Invalidaddress)

fmtPrintln(TheaddressisaddrString())

osExit(0)

ItreturnsthecorrespondingIPformatforagivenIPaddress

TCPsocketWhatcanwedowhenweknowhowtovisitawebservicethroughanetworkportAsaclientwecansendarequesttoanappointednetworkportandgetsitsresponseasaserverweneedtobindaservicetoanappointednetworkportwaitforclientsrequestsandsupplyaresponse

InGosnetpackagetheresatypecalledTCPConnthatfacilitatesthiskindofclientsserversinteractionThistypehastwokeyfunctions

func(cTCPConn)Write(b[]byte)(ninterrosError)

func(cTCPConn)Read(b[]byte)(ninterrosError)

TCPConncanbeusedbyeitherclientorserverforreadingandwritingdata

WealsoneedaTCPAddrtorepresentTCPaddressinformation

Sockets

typeTCPAddrstruct

Portint

WeusetheResolveTCPAddrfunctiontogetaTCPAddrinGo

funcResolveTCPAddr(netaddrstring)(TCPAddrosError)

Argumentsofnetcanbeoneoftcp4tcp6ortcpwhicheachsignifyIPv4-onlyIPv6-onlyandeitherIPv4orIPv6respectivelyaddrcanbeadomainnameorIPaddresslikewwwgooglecom80or12700122

TCPclientGoclientsusetheDialTCPfunctioninthenetpackagetocreateaTCPconnectionwhichreturnsaTCPConnobjectafteraconnectionisestablishedtheserverhasthesametypeofconnectionobjectforthecurrentconnectionandclientandservercanbeginexchangingdatawithoneanotherIngeneralclientssendrequeststoserversthroughaTCPConnandreceiveinformationfromtheserverresponseserversreadandparseclientrequeststhenreturnfeedbackThisconnectionwillremainvaliduntileithertheclientorserverclosesitThefunctionforcreatingaconnectionisasfollows

funcDialTCP(netstringladdrraddrTCPAddr)(cTCPConnerrosError)

Argumentsofnetcanbeoneoftcp4tcp6ortcpwhicheachsignifyIPv4-onlyIPv6-onlyandeitherIPv4orIPv6respectivelyladdrrepresentsthelocaladdresssetittonilinmostcasesraddrrepresentstheremoteaddress

LetswriteasimpleexampletosimulateaclientrequestingaconnectiontoaserverbasedonanHTTPrequestWeneedasimpleHTTPrequestheader

HEADHTTP10rnrn

Serverresponseinformationformatmaylooklikethefollowing

HTTP10200OK

ETag-9985996

Last-ModifiedThu25Mar2010175110GMT

Content-Length18074

Connectionclose

DateSat28Aug2010004348GMT

Serverlighttpd1423

Clientcode

Sockets

packagemain

import(

ioioutil

funcmain()

iflen(osArgs)=2

fmtFprintf(osStderrUsageshostportosArgs[0])

osExit(1)

service=osArgs[1]

tcpAddrerr=netResolveTCPAddr(tcp4service)

checkError(err)

connerr=netDialTCP(tcpniltcpAddr)

checkError(err)

_err=connWrite([]byte(HEADHTTP10rnrn))

checkError(err)

resulterr=ioutilReadAll(conn)

checkError(err)

fmtPrintln(string(result))

osExit(0)

funccheckError(errerror)

iferr=nil

fmtFprintf(osStderrFatalerrorserrError())

osExit(1)

IntheaboveexampleweuseuserinputastheserviceargumentofnetResolveTCPAddrtogetatcpAddrPassingtcpAddrtotheDialTCPfunctionwecreateaTCPconnectionconnWecanthenuseconntosendrequestinformationtotheserverFinallyweuseioutilReadAlltoreadallthecontentfromconnwhichcontainstheserverresponse

TCPserver

WehaveaTCPclientnowWecanalsousethenetpackagetowriteaTCPserverOntheserversideweneedtobindourservicetoaspecificinactiveportandlistenforanyincomingclientrequests

funcListenTCP(netstringladdrTCPAddr)(lTCPListenererrosError)

func(lTCPListener)Accept()(cConnerrosError)

TheargumentsrequiredhereareidenticaltothoserequiredbytheDialTCPfunctionweusedearlierLetsimplementatimesyncingserviceusingport7777

Sockets

packagemain

import(

funcmain()

service=7777

checkError(err)

listenererr=netListenTCP(tcptcpAddr)

checkError(err)

connerr=listenerAccept()

iferr=nil

continue

daytime=timeNow()String()

connWrite([]byte(daytime))dontcareaboutreturnvalue

connClose()werefinishedwiththisclient

iferr=nil

osExit(1)

AftertheserviceisstarteditwaitsforclientrequestsWhenitreceivesaclientrequestitAcceptsitandreturnsaresponsetotheclientcontaininginformationaboutthecurrenttimeItsworthnotingthatwhenerrorsoccurintheforlooptheservicecontinuesrunninginsteadofexitingInsteadofcrashingtheserverwillrecordtheerrortoaservererrorlog

TheabovecodeisstillnotgoodenoughhoweverWedidntmakeuseofgoroutineswhichwouldhaveallowedustoacceptsimultaneousrequestsLetsdothisnow

Sockets

packagemain

import(

funcmain()

service=1200

checkError(err)

iferr=nil

continue

gohandleClient(conn)

funchandleClient(connnetConn)

deferconnClose()

werefinishedwiththisclient

iferr=nil

osExit(1)

ByseparatingoutourbusinessprocessfromthehandleClientfunctionandbyusingthegokeywordwevealreadyimplementedconcurrencyinourserviceThisisagooddemonstrationofthepowerandsimplicityofgoroutines

SomeofyoumaybethinkingthefollowingthisserverdoesnotdoanythingmeaningfulWhatifweneededtosendmultiplerequestsfordifferenttimeformatsoverasingleconnectionHowwouldwedothat

Sockets

packagemain

import(

strconv

funcmain()

service=1200

checkError(err)

iferr=nil

continue

connSetReadDeadline(timeNow()Add(2timeMinute))set2minutestimeout

request=make([]byte128)setmaximumrequestlengthto128Btopreventfloodbasedattacks

deferconnClose()closeconnectionbeforeexit

read_lenerr=connRead(request)

iferr=nil

fmtPrintln(err)

ifread_len==0

breakconnectionalreadyclosedbyclient

elseifstring(request[read_len])==timestamp

daytime=strconvFormatInt(timeNow()Unix()10)

connWrite([]byte(daytime))

iferr=nil

osExit(1)

InthisexampleweuseconnRead()toconstantlyreadclientrequestsWecannotclosetheconnectionbecauseclientsmayissuemorethanonerequestDuetothetimeoutwesetusingconnSetReadDeadline()theconnectionclosesautomaticallyafterourallottedtimeperiodWhentheexpirytimehaselapsedourprogrambreaksfromtheforloopNoticethatrequestneedstobecreatedwithamaxsizelimitationinordertopreventfloodattacks

ControllingTCPconnections

ControllingTCPfunctions

funcDialTimeout(netaddrstringtimeouttimeDuration)(Connerror)

Sockets

SettingthetimeoutofconnectionsThesearesuitableforuseonbothclientsandservers

func(cTCPConn)SetReadDeadline(ttimeTime)error

func(cTCPConn)SetWriteDeadline(ttimeTime)error

Settingthewritereadtimeoutofoneconnection

func(cTCPConn)SetKeepAlive(keepalivebool)osError

ItsworthtakingsometimetothinkabouthowlongyouwantyourconnectiontimeoutstobeLongconnectionscanreducetheamountofoverheadinvolvedincreatingconnectionsandaregoodforapplicationsthatneedtoexchangedatafrequently

FormoredetailedinformationjustlookuptheofficialdocumentationforGosnetpackage

UDPsocketsTheonlydifferencebetweenaUDPsocketandaTCPsocketistheprocessingmethodfordealingwithmultiplerequestsonserversideThisarisesfromthefactthatUDPdoesnothaveafunctionlikeAcceptAlloftheotherfunctionshaveUDPcounterpartsjustreplaceTCPwithUDPinthefunctionsmentionedabove

funcResolveUDPAddr(netaddrstring)(UDPAddrosError)

funcDialUDP(netstringladdrraddrUDPAddr)(cUDPConnerrosError)

funcListenUDP(netstringladdrUDPAddr)(cUDPConnerrosError)

func(cUDPConn)ReadFromUDP(b[]byte)(nintaddrUDPAddrerrosError

func(cUDPConn)WriteToUDP(b[]byteaddrUDPAddr)(ninterrosError)

UDPclientcodesample

packagemain

import(

funcmain()

iflen(osArgs)=2

osExit(1)

service=osArgs[1]

udpAddrerr=netResolveUDPAddr(udp4service)

checkError(err)

connerr=netDialUDP(udpniludpAddr)

checkError(err)

_err=connWrite([]byte(anything))

checkError(err)

varbuf[512]byte

nerr=connRead(buf[0])

checkError(err)

fmtPrintln(string(buf[0n]))

osExit(0)

iferr=nil

fmtFprintf(osStderrFatalerrorerrError())

osExit(1)

Sockets

UDPservercodesample

packagemain

import(

funcmain()

service=1200

checkError(err)

connerr=netListenUDP(udpudpAddr)

checkError(err)

handleClient(conn)

funchandleClient(connnetUDPConn)

varbuf[512]byte

_addrerr=connReadFromUDP(buf[0])

iferr=nil

return

connWriteToUDP([]byte(daytime)addr)

iferr=nil

osExit(1)

SummaryThroughdescribingandcodingsomesimpleprogramsusingTCPandUDPsocketswecanseethatGoprovidesexcellentsupportforsocketprogrammingandthattheyarefunandeasytouseGoalsoprovidesmanyfunctionsforbuildinghighperformancesocketapplications

LinksDirectoryPrevioussectionWebservicesNextsectionWebSocket

Sockets

82WebSocketsWebSocketsareanimportantfeatureofHTML5Itimplementsbrowserbasedremotesocketswhichallowsbrowserstohavefull-duplexcommunicationswithserversMainstreambrowserslikeFirefoxGoogleChromeandSafariprovidesupportforthisWebSockets

PeopleoftenusedrollpollingforinstantmessagingservicesbeforeWebSocketswerebornwhichallowclientstosendHTTPrequestsperiodicallyTheserverthenreturnsthelatestdatatoclientsThedownsidetothismethodisthatitrequiresclientstokeepsendingmanyrequeststotheserverwhichcanconsumealargeamountofbandwidth

WebSocketsuseaspecialkindofheaderthatreducesthenumberofhandshakesrequiredbetweenbrowserandservertoonlyoneforestablishingaconnectionThisconnectionwillremainactivethroughoutitslifetimeandyoucanuseJavaScripttowriteorreaddatafromthisconnectionasinthecaseofaconventionalTCPsocketsItsolvesmanyoftheheadacheinvolvedwithreal-timewebdevelopmentandhasthefollowingadvantagesovertraditionalHTTP

OnlyoneTCPconnectionforasinglewebclientWebSocketserverscanpushdatatowebclientsLightweightheadertoreducedatatransmissionoverhead

WebSocketURLsbeginwithwsorwss(SSL)ThefollowingfigureshowsthecommunicationprocessofWebSocketsAparticularHTTPheaderissenttotheserveraspartofthehandshakingprotocolandtheconnectionisestablishedThenserversorclientsareabletosendorreceivedatathroughJavaScriptviaWebSocketThissocketcanthenbeusedbyaneventhandlertoreceivedataasynchronously

Figure82WebSocketprinciple

WebSocketprinciplesTheWebSocketprotocolisactuallyquitesimpleAftersuccessfullycompletingtheinitialhandshakeaconnectionisestablishedSubsequentdatacommunicationswillallbeginwithx00andendwithxFFThisprefixandsuffixwillbevisibletoclientsbecausetheWebSocketwillbreakoffbothendyieldingtherawdataautomatically

WebSocketconnectionsarerequestedbybrowsersandrespondedtobyserversafterwhichtheconnectionisestablishedThisprocessisoftencalledhandshaking

Considerthefollowingrequestsandresponses

Figure83WebSocketrequestandresponse

Sec-WebSocket-keyisgeneratedrandomlyasyoumayhavealreadyguessedanditsbase64encodedServersneedtoappendthiskeytoafixedstringafteracceptingarequest

258EAFA5-E914-47DA-95CA-C5AB0DC85B11

Supposewehavef7cb4ezEAl6C3wRaU6JORA==thenwehave

f7cb4ezEAl6C3wRaU6JORA==258EAFA5-E914-47DA-95CA-C5AB0DC85B11

Usesha1tocomputethebinaryvalueandusebase64toencodeitWewillthenwehave

rE91AJhfC+6JdVcVXOGJEADEJdQ=

WebSocket

UsethisasthevalueoftheSec-WebSocket-Acceptresponseheader

WebSocketinGoTheGostandardlibrarydoesnotsupportWebSocketsHoweverthewebsocketpackagewhichisasub-packageofgonetdoesandisofficiallymaintainedandsupported

Usegogettoinstallthispackage

gogetgolangorgxnetwebsocket

WebSocketshavebothclientandserversidesLetsseeasimpleexamplewhereauserinputssomeinformationontheclientsideandsendsittotheserverthroughaWebSocketfollowedbytheserverpushinginformationbacktotheclient

Clientcode

lthtmlgt

ltheadgtltheadgt

ltbodygt

ltscripttype=textjavascriptgt

varsock=null

varwsuri=ws1270011234

windowonload=function()

consolelog(onload)

sock=newWebSocket(wsuri)

sockonopen=function()

consolelog(connectedto+wsuri)

sockonclose=function(e)

consolelog(connectionclosed(+ecode+))

sockonmessage=function(e)

consolelog(messagereceived+edata)

functionsend()

varmsg=documentgetElementById(message)value

socksend(msg)

ltscriptgt

lth1gtWebSocketEchoTestlth1gt

ltformgt

Messageltinputid=messagetype=textvalue=Helloworldgt

ltformgt

ltbuttononclick=send()gtSendMessageltbuttongt

ltbodygt

lthtmlgt

AsyoucanseeitsveryeasytousetheclientsideJavaScriptfunctionstoestablishaconnectionTheonopeneventgetstriggeredaftersuccessfullycompletingtheaforementionedhandshakingprocessIttellstheclientthattheconnectionhasbeencreatedsuccessfullyClientsattemptingtoopenaconnectiontypicallybindtofourevents

1）onopentriggeredafterconnectionhasbeenestablished2）onmessagetriggeredafterreceivingamessage3）onerrortriggeredafteranerrorhasoccurred

WebSocket

4）onclosetriggeredaftertheconnectionhasclosed

Servercode

packagemain

import(

golangorgxnetwebsocket

nethttp

funcEcho(wswebsocketConn)

varerrerror

varreplystring

iferr=websocketMessageReceive(wsampreply)err=nil

fmtPrintln(Cantreceive)

fmtPrintln(Receivedbackfromclient+reply)

msg=Received+reply

fmtPrintln(Sendingtoclient+msg)

iferr=websocketMessageSend(wsmsg)err=nil

fmtPrintln(Cantsend)

funcmain()

httpHandle(websocketHandler(Echo))

iferr=httpListenAndServe(1234nil)err=nil

WhenaclientSendsuserinputinformationtheserverReceivesitandusesSendonceagaintoreturnaresponse

Figure84WebSocketserverreceivedinformation

ThroughtheexampleabovewecanseethattheclientandserversideimplementationofWebSocketsisveryconvenientWecanusethenetpackagedirectlyinGoWiththerapiddevelopmentofHTML5IthinkthatWebSocketswilltakeonamuchmoreimportantroleinmoderndaywebdevelopmentweshouldallbeatleastalittlebitfamiliarwiththem

LinksDirectoryPrevioussectionSocketsNextsectionREST

WebSocket

83RESTRESTisthemostpopularsoftwarearchitectureontheinternettodaybecauseitisfoundedonwelldefinedstrictstandardsanditseasytounderstandandexpandMoreandmorewebsitesarebasingtheirdesignsontopofRESTInthissectionwearegoingtohaveacloselookatimplementingtheRESTarchitectureinGoand(hopefully)learnhowtoleverageittoourbenefit

WhatisRESTThefirstdeclarationoftheconceptofREST(REpresentationalStateTransfer)wasintheyear2000inRoyThomasFieldingsdoctoraldissertationwhoalsojusthappenstobetheco-founderoftheHTTPprotocolItspecifiesthearchitecturesconstraintsandprinciplesandanythingimplementedwiththisarchitecturecanbecalledaRESTfulsystem

BeforeweunderstandwhatRESTisweneedtocoverthefollowingconcepts

Resources

RESTisthePresentationLayerStateTransferwherethepresentationlayerisactuallytheresourcepresentatio

nlayer

SowhatareresourcesPicturesdocumentsorvideosetcareallexamplesofresourcesandcanbelocatedby

Representation

ResourcesarespecificinformationentitiesthatcanbeshowninavarietyofwayswithinthepresentationlayerForinstanceaTXTdocumentcanberepresentedasHTMLJSONXMLetcanimagecanberepresentedasjpgpngetc

URIsareusedtoidentifyresourcesbuthowdowedetermineitsspecificmanifestationsYouarereferredtotheAcceptandContent-TypeinanHTTPrequestheaderthesetwofieldsdescribethepresentationlayer

StateTransfer

AninteractiveprocessisinitiatedbetweenclientandservereachtimeyouvisitanypageofawebsiteDuringthisprocesscertaindatarelatedtothecurrentpagestateneedtobesavedHoweveryoullrecallthatHTTPisastatelessprotocolItsobviousthatweneedtosavethisclientstateonourserversideItfollowsthatifaclientmodifiessomedataandwantstopersistthechangestheremustbeawaytoinformtheserversideaboutthenewstate

MostofthetimeclientsinformserversofstatechangesusingHTTPTheyhavefouroperationswithwhichtodothis

-GETisusedtoobtainresources-POSTsisusedtocreateorupdateresources-PUTupdatesresources-DELETEdeletesresources

Tosummarizetheabove

（1）EveryURIrepresentsaresource（2）Thereisarepresentationlayerfortransferringresourcesbetweenclientsandservers（3）ClientsusefourHTTPmethodstoimplementPresentationLayerStateTransferallowingthemtooperateonremoteresources

ThemostimportantprincipleofwebapplicationsthatimplementRESTisthattheinteractionbetweenclientsandserversarestatelesseveryrequestshouldencapsulatealloftherequiredinformationServersshouldbeabletorestartatanytimewithouttheclientsbeingnotifiedInadditionrequestscanberespondedbyanyserverofthesameservicewhichisidealforcloudcomputingLastlybecauseitsstatelessclientscancachedataforimprovingperformance

AnotherimportantprincipleofRESTissystemdelaminationwhichmeansthatcomponentsinonelayerhavenowayofinteractingdirectlywithcomponentsinotherlayersThiscanlimitsystemcomplexityandencourageindependenceintheunderlyingcomponents

Figure85RESTarchitecture

WhenRESTfulconstraintsarejudiciouslyabidedbywebapplicationscanbescaledtoaccommodatemassivenumbersofclientsUsingtheRESTarchitecturecanalsohelpreducedelaysbetweenclientsandserverssimplifysystemarchitectureandimprovethevisibilityofsub-systemendpoints

Figure86RESTsexpansibility

RESTfulimplementationGodoesnthavedirectsupportforRESTbutsinceRESTfulwebapplicationsareallHTTP-basedwecanusethenethttppackagetoimplementitonourownOfcoursewewillfirstneedtomakesomemodificationsbeforeweareabletofullyimplementREST

RESTusesdifferentmethodstohandleresourcesdependingontheinteractionthatsrequiredwiththatresourceManyexistingapplicationsclaimtobeRESTfulbuttheydonotactuallyimplementRESTImgoingtocategorizetheseapplicationsintoseverallevelsdependsonwhichHTTPmethodstheyimplement

Figure87RESTslevel

ThepictureaboveshowsthreelevelsthatarecurrentlyimplementedinRESTYoumaynotchoosetofollowalltherulesandconstraintsofRESTwhendevelopingyourownapplicationsbecausesometimesitsrulesarenotagoodfitforallsituationsRESTfulwebapplicationsuseeverysingleHTTPmethodincludingDELETEandPUTbutinmanycasesHTTPclientscanonlysendGETandPOSTrequests

HTMLstandardallowsclientssendGETandPOSTrequeststhroughlinksandformsItsnotpossibletosendPUTorDELETErequestswithoutAJAXsupportSomefirewallsinterceptPUTandDELETErequestsandclientshavetousePOSTinordertoimplementthemFullyRESTfulservicesareinchargeoffindingtheoriginalHTTPmethodsandrestoringthem

WecansimulatePUTandDELETErequestsbyaddingahidden_methodfieldinourPOSTrequestshowevertheserequestsmustbeconvertedontheserversidebeforetheyareprocessedMypersonalapplicationsusethisworkflowtoimplementRESTinterfacesStandardRESTfulinterfacesareeasilyimplementedinGoasthefollowingexampledemonstrates

packagemain

import(

githubcomjulienschmidthttprouter

nethttp

funcIndex(whttpResponseWriterrhttpRequest_httprouterParams)

fmtFprint(wWelcomen)

funcHello(whttpResponseWriterrhttpRequestpshttprouterParams)

fmtFprintf(whellosnpsByName(name))

funcgetuser(whttpResponseWriterrhttpRequestpshttprouterParams)

uid=psByName(uid)

fmtFprintf(wyouaregetusersuid)

funcmodifyuser(whttpResponseWriterrhttpRequestpshttprouterParams)

uid=psByName(uid)

fmtFprintf(wyouaremodifyusersuid)

funcdeleteuser(whttpResponseWriterrhttpRequestpshttprouterParams)

uid=psByName(uid)

fmtFprintf(wyouaredeleteusersuid)

funcadduser(whttpResponseWriterrhttpRequestpshttprouterParams)

uid=rFormValue(uid)

uid=psByName(uid)

fmtFprintf(wyouareaddusersuid)

funcmain()

router=httprouterNew()

routerGET(Index)

routerGET(hellonameHello)

routerGET(useruidgetuser)

routerPOST(adduseruidadduser)

routerDELETE(deluseruiddeleteuser)

routerPUT(moduseruidmodifyuser)

logFatal(httpListenAndServe(8080router))

ThissamplecodeshowsyouhowtowriteaverybasicRESTapplicationOurresourcesareusersandweusedifferentfunctionsfordifferentmethodsHereweimportedathird-partypackagecalledgithubcomjulienschmidthttprouterWevealreadycoveredhowtoimplementacustomrouterinpreviouschapters-thejulienschmidthttprouterpackageimplementssomeveryconvenientroutermappingrulesthatmakeitveryconvenientforimplementingRESTfularchitectureAsyoucanseeRESTrequiresyoutoimplementdifferentlogicfordifferentHTTPmethodsofthesameresource

SummaryRESTisastyleofwebarchitecturebuildingonpastsuccessfulexperienceswithWWWstatelessnessresource-centricfulluseofHTTPandURIprotocolsandtheprovisionofunifiedinterfacesThesesuperiordesignconsiderationshaveallowedRESTtobecomethemostpopularwebservicesstandardInasensebyemphasizingtheURIandleveraging

earlyInternetstandardssuchasHTTPRESThaspavedthewayforlargeandscalablewebapplicationsCurrentlythesupportthatGohasForRESTisstillverybasicHoweverbyimplementingcustomroutingrulesanddifferentrequesthandlersforeachtypeofHTTPrequestwecanachieveRESTfularchitectureinourGowebapps

LinksDirectoryPrevioussectionWebSocketNextsectionRPC

84RPCInprevioussectionswetalkedabouthowtowritenetworkapplicationsbasedonSocketsandHTTPWelearnedthatbothofthemusetheinformationexchangemodelinwhichclientssendrequestsandserversrespondtothemThiskindofdataexchangeisbasedonaspecificformatsothatbothsidesareabletocommunicatewithoneanotherHowevermanyindependentapplicationsdonotusethismodelbutinsteadcallservicesjustliketheywouldcallnormalfunctions

RPCwasintendedtobethefunctioncallmodefornetworkedsystemsClientsexecuteRPCsliketheycallnativefunctionsexcepttheypackagethefunctionparametersandsendthemthroughthenetworktotheserverTheservercanthenunpacktheseparametersandprocesstherequestexecutingtheresultsbacktotheclient

Incomputersciencearemoteprocedurecall(RPC)isatypeofinter-processcommunicationthatallowsacomputerprogramtocauseasubroutineorproceduretoexecuteinanotheraddressspace(commonlyonanothercomputeronasharednetwork)withouttheprogrammerexplicitlycodingthedetailsforthisremoteinteractionThatistheprogrammerwritesessentiallythesamecodewhetherthesubroutineislocaltotheexecutingprogramorremoteWhenthesoftwareinquestionusesobject-orientedprinciplesRPCiscalledremoteinvocationorremotemethodinvocation

RPCworkingprinciple

Figure88RPCworkingprinciple

NormallyanRPCcallfromclienttoserverhasthefollowingtensteps

1 Calltheclienthandleexecutetransferarguments

1 Calllocalsystemkerneltosendnetworkmessages

1 Sendmessagestoremotehosts

1 Theserverreceiveshandleandarguments

1 Executeremoteprocesses

1 Returnexecutionresulttocorrespondinghandle

1 Theserverhandlecallsremotesystemkernel

1 Messagessentbacktolocalsystemkernel

1 Theclienthandlereceivesmessagesfromsystemkernel

1 Theclientgetsresultsfromcorrespondinghandle

GoRPCGohasofficialsupportforRPCinitsstandardlibraryonthreelevelswhichareTCPHTTPandJSONRPCNotethatGoRPCisnotlikeothertraditionalRPCsystemsItrequiresyoutouseGoapplicationsonbothclientandserversidesbecauseitencodescontentusingGob

FunctionsofGoRPCmustabidebythefollowingrulesforremoteaccessotherwisethecorrespondingcallswillbeignored

Functionsareexported(capitalized)FunctionsmusthavetwoargumentswithexportedtypesThefirstargumentisforreceivingfromtheclientandthesecondonehastobeapointerandisforreplyingtotheclientFunctionsmusthaveareturnvalueoferrortype

Forexample

func(tT)MethodName(argTypeT1replyTypeT2)error

WhereTT1andT2mustbeabletobeencodedbythepackagegobpackage

AnykindofRPChastogothroughanetworktotransferdataGoRPCcaneitheruseHTTPorTCPThebenefitsofusingHTTPisthatyoucanreusesomefunctionsfromthenethttppackage

HTTPRPCHTTPserversidecode

packagemain

import(

errors

nethttp

netrpc

typeArgsstruct

typeQuotientstruct

QuoRemint

typeArithint

func(tArith)Multiply(argsArgsreplyint)error

reply=argsAargsB

returnnil

func(tArith)Divide(argsArgsquoQuotient)error

ifargsB==0

returnerrorsNew(dividebyzero)

quoQuo=argsAargsB

quoRem=argsAargsB

returnnil

funcmain()

arith=new(Arith)

rpcRegister(arith)

rpcHandleHTTP()

err=httpListenAndServe(1234nil)

iferr=nil

fmtPrintln(errError())

WeregisteredaRPCserviceofAriththenregisteredthisserviceonHTTPthroughrpcHandleHTTPAfterthatweareabletotransferdatathroughHTTP

Clientsidecode

packagemain

import(

netrpc

typeArgsstruct

typeQuotientstruct

QuoRemint

funcmain()

iflen(osArgs)=2

fmtPrintln(UsageosArgs[0]server)

osExit(1)

serverAddress=osArgs[1]

clienterr=rpcDialHTTP(tcpserverAddress+1234)

iferr=nil

logFatal(dialingerr)

Synchronouscall

args=Args178

varreplyint

err=clientCall(ArithMultiplyargsampreply)

iferr=nil

logFatal(aritherrorerr)

fmtPrintf(Arithdd=dnargsAargsBreply)

varquotQuotient

err=clientCall(ArithDivideargsampquot)

iferr=nil

fmtPrintf(Arithdd=dremainderdnargsAargsBquotQuoquotRem)

WecompiletheclientandtheserversidecodeseparatelythenstarttheserverandclientYoullthenhavesomethingsimilarasfollowsafteryouinputsomedata

$http_clocalhost

Arith178=136

Arith178=2remainder1

AsyoucanseewedefinedastructforthereturntypeWeuseitastypeoffunctionargumentontheserversideandasthetypeofthesecondandthirdargumentsontheclientclientCallThiscallisveryimportantIthasthreeargumentswherethefirstoneisthenameofthefunctionthatisgoingtobecalledthesecondistheargumentyouwanttopassandthelastoneisthereturnvalue(ofpointertype)SofarweseethatitseasytoimplementRPCinGo

TCPRPCLetstrytheRPCthatisbasedonTCPhereistheserversidecode

packagemain

import(

errors

netrpc

typeArgsstruct

typeQuotientstruct

QuoRemint

typeArithint

reply=argsAargsB

returnnil

ifargsB==0

quoQuo=argsAargsB

quoRem=argsAargsB

returnnil

funcmain()

arith=new(Arith)

rpcRegister(arith)

tcpAddrerr=netResolveTCPAddr(tcp1234)

checkError(err)

iferr=nil

continue

rpcServeConn(conn)

iferr=nil

fmtPrintln(FatalerrorerrError())

osExit(1)

ThedifferencebetweenHTTPRPCandTCPRPCisthatwehavetocontrolconnectionsbyourselvesifweuseTCPRPCthenpassconnectionstoRPCforprocessing

AsyoumayhaveguessedthisisablockingpatternYouarefreetousegoroutinestoextendthisapplicationasamoreadvancedexperiment

Theclientsidecode

packagemain

import(

netrpc

typeArgsstruct

typeQuotientstruct

QuoRemint

funcmain()

iflen(osArgs)=2

fmtPrintln(UsageosArgs[0]serverport)

osExit(1)

service=osArgs[1]

clienterr=rpcDial(tcpservice)

iferr=nil

Synchronouscall

args=Args178

varreplyint

iferr=nil

varquotQuotient

iferr=nil

TheonlydifferenceintheclientsidecodeisthatHTTPclientsuseDialHTTPwhereasTCPclientsuseDial(TCP)

JSONRPC

JSONRPCencodesdatatoJSONinsteadofgobLetsseeanexampleofaGoJSONRPContheserver

packagemain

import(

errors

netrpc

netrpcjsonrpc

typeArgsstruct

typeQuotientstruct

QuoRemint

typeArithint

reply=argsAargsB

returnnil

ifargsB==0

quoQuo=argsAargsB

quoRem=argsAargsB

returnnil

funcmain()

arith=new(Arith)

rpcRegister(arith)

checkError(err)

iferr=nil

continue

jsonrpcServeConn(conn)

iferr=nil

osExit(1)

JSONRPCisbasedonTCPanddoesntsupportHTTPyet

Theclientsidecode

packagemain

import(

netrpcjsonrpc

typeArgsstruct

typeQuotientstruct

QuoRemint

funcmain()

iflen(osArgs)=2

logFatal(1)

service=osArgs[1]

clienterr=jsonrpcDial(tcpservice)

iferr=nil

Synchronouscall

args=Args178

varreplyint

iferr=nil

varquotQuotient

iferr=nil

SummaryGohasgoodsupportforHTTPTPCandJSONRPCimplementationwhichallowustoeasilydevelopdistributedwebapplicationshoweveritisregrettablethatGodoesnthavebuilt-insupportforSOAPRPCalthoughsomeopensourcethird-partypackagesdoofferthis

LinksDirectoryPrevioussectionRESTNextsectionSummary

85SummaryInthischapterIintroducedyoutoseveralmainstreamwebapplicationdevelopmentmodelsInsection81IdescribedthebasicsofnetworkprogrammingsocketsBecauseoftherapidevolutionofnetworktechnologyandinfrastructureandgiventhattheSocketisthecornerstoneofthesechangesyoumustmastertheconceptsbehindsocketprogramminginordertobeacompetentwebdeveloperInsection82IdescribedHTML5WebSocketswhichsupportfull-duplexcommunicationsbetweenclientandserverandeliminatetheneedforpollingwithAJAXInsection83weimplementedasimpleapplicationusingtheRESTarchitecturewhichisparticularlysuitableforthedevelopmentofnetworkAPIsduetotherapidriseofmobileapplicationsIbelievethatRESTfulAPIswillbeanongoingtrendInsection84welearnedaboutGoRPCs

GoprovidesexcellentsupportforthefourkindsofdevelopmentmethodsmentionedaboveNotethatthenetpackageanditssub-packagesistheplacewhereGosnetworkprogrammingtoolsGoresideIfyouwantamorein-depthunderstandingoftherelevantimplementationdetailsyoushouldtryreadingthesourcecodeofthosepackages

LinksDirectoryPrevioussectionRPCNextchapterSecurityandencryption

Summary

9SecurityandencryptionSecurityisanextremelyimportantaspectofmostwebapplicationsThistopichasbeengettingmoreandmoreattentionlatelyespeciallyinlightoftherecentCSDNLinkedinandYahoopasswordleaksAsGodeveloperswemustbeawareofvulnerabilitiesinourapplicationsandtakeprecautionsinordertopreventattackersfromtakingoveroursystems

Manyofthesecurityproblemsthatariseinmodernwebapplicationsoriginatefromdataprovidedbythird-partiesForexampleuserinputshouldalwaysbevalidatedandsanitizedbeforebeingstoredassecuredataIfthisisntdonewhenthedataisoutputtedtoaclientitmaycauseacross-sitescriptingattack(XSS)SimilarlyifunsafedataisuseddirectlyasyourapplicationsdatabasequeriesthenyoumaybevulnerabletoSQLinjectionattacksInsections93and94welllookathowtoavoidtheseproblems

Whenusingthird-partydata(whichincludesuser-supplieddata)firstverifytheintegrityofthedatabyfilteringtheinputSection92willdescribehowtofilterinput

UnfortunatelyfilteringinputandescapingoutputdoesnotsolveallsecurityproblemsInsection91wewillexplaincross-siterequestforgery(CSRF)attacksThisisamaliciousexploitwhereunauthorizedcommandsaretransmittedfromauserthatthewebsitetrusts

KeepingconfidentialdataencryptedcanalsohelpyoutosecureyourwebapplicationsInsection95wewilldescribehowtostorepasswordssafelyusingGosencryptionpackage

AgoodhashfunctionmakesithardtofindtwostringsthatwouldproducethesamehashvalueandthisisonewaywithwhichwecanencryptourdataThereisalsotwo-wayencryptionwhereyouuseasecretkeytodecryptencrypteddataInsection96wewilldescribehowtoperformbothone-wayandtwo-wayencryption

LinksDirectoryPreviousChapterChapter8SummaryNextsectionCSRFattacks

91CSRFattacks

WhatisCSRFCSRFandXSRFbothstandforCross-siterequestforgeryItsalsoknownasaoneclickattackorsessionriding

SohowdoesaCSRFattackworkACSRFattackhappenswhenanattackertricksatrusteduserintoaccessingawebsiteorclickingaURLthattransmitsmaliciousrequests(withouttheuserrsquosconsent)toatargetedwebsiteHeresasimpleexampleusingafewsocialengineeringtricksanattackercouldusetheQQchatsoftwaretofindandsendmaliciouslinkstovictimstargetedattheirusersonlinebankingwebsiteIfthevictimlogsintotheironlinebankaccountanddoesnotexitthenclickingonamaliciouslinksentfromtheattackercouldallowtheattackertostealalloftheusersbankaccountfunds

WhenunderaCSRFattackasingleend-userwithanadministratoraccountcanthreatentheintegrityoftheentirewebapplication

CSRFprincipleThefollowingdiagramprovidesasimpleoverviewofaCSRFattack

Figure91CSRFattackprocess

AscanbeseenfromthefiguretocompleteaCSRFattackthevictimmustcompletethefollowingtwosteps

-1LogintotrustedsiteAandstorealocalCookie-2WithoutgoingthroughexistingsiteAaccessthedangerouslinktositeB

AsareaderyoumaybeaskingIfIdonotmeettheabovetwoconditionsIwillnotbesubjectedtoCSRFattacksYesthisistruehoweveryoucannotguaranteethatthefollowingdoesnotoccur

YoucannotguaranteethatwhenyouareloggedintoasitethesitedidntlaunchanyhiddentabsYoucannotguaranteethatwhenyoucloseyourbrowseryourcookieswillimmediatelyexpireandyourlastsessionwillhaveendedTrustedhightrafficwebsiteswilllikelynothavehiddenvulnerabilitieseasilyexploitablebyCSRFbasedattacks

ThusitcanbedifficultforuserstovisitawebsitethroughalinkandknowthatitwillnotcarryoutunknownoperationsintheformofaCSRFattack

CSRFattacksworkmostlybecauseoftheprocessthroughwhichusersareauthenticatedAlthoughyoucanreasonablyguaranteethatarequestoriginatesfromausersbrowserthereisnoguaranteethattheusergrantedapprovalfortherequest

HowtopreventCSRFattacksYoumightbealittlescaredafterreadingthesectionaboveButfearisagoodthingItwillforceyoutoeducateyourselfonhowtopreventvulnerabilitieslikethisfromhappeningtoyou

PreventativemeasuresagainstCSRFattackscanbetakenonboththeserverandclientsidesofawebapplicationHoweverCSRFattacksaremosteffectivelythwartedontheserverside

TherearemanywaysofpreventingCSRFattacksontheserversideMostapproachesstemfromthefollowingtwoaspects

1 MaintainingproperuseofGETPOSTandcookies

CSRFattacks

2 Includingapseudo-randomnumberwithnon-GETrequests

InthepreviouschapteronRESTwesawhowmostwebapplicationsarebasedonGETandPOSTHTTPrequestsandthatcookieswereincludedalongwiththeserequestsWegenerallydesignapplicationsaccordingtothefollowingprinciples

1 GETiscommonlyusedtoviewinformationwithoutalteringanydata

2 POSTisusedinplacingorderschangingthepropertiesofaresourceorperformingothertasks

ImnowgoingtousetheGolanguagetoillustratehowtorestrictaccesstoresourcesmethods

muxGet(useruidgetuser)

muxPost(useruidmodifyuser)

SincewevestipulatedthatmodificationscanonlyusePOSTwhenaGETmethodisissuedinsteadofaPOSTwecanrefusetorespondtotherequestAccordingtothefigureaboveattacksutilizingGETasaCSRFexploitcanbepreventedIsthisenoughtopreventallpossibleCSRFattacksOfcoursenotbecausePOSTscanalsobeforged

Weneedtoimplementasecondstepwhichis(inthecaseofnon-GETrequests)toincreasethelengthofthepseudo-randomnumberincludedwiththerequestThisusuallyinvolvessteps

Foreachusergenerateauniquecookietokenwithapseudo-randomvalueAllformsmustcontainthesamepseudo-randomvalueThisproposalisthesimplestonebecauseintheoryanattackercannotreadthirdpartycookiesAnyformthatanattackermaysubmitwillfailthevalidationprocesswithoutknowingwhattherandomvalueisDifferentformscontaindifferentpseudo-randomvaluesasweveintroducedinsection44HowtopreventmultipleformsubmissionWecanreusetherelevantcodefromthatsectiontomeetourneeds

Generatingarandomnumbertoken

h=md5New()

ioWriteString(hganraomaxxxxxxxxx)

tExecute(wtoken)

Outputtoken

Authenticationtoken

rParseForm()

iftoken=

Verificationtokenoflegitimacy

Errortokendoesnotexist

WecanusetheprecedingcodetosecureourPOSTsYoumightbewonderinginaccordancewithourtheorywhethertherecouldbesomewayforamaliciousthirdpartytosomehowfigureoutoursecrettokenvalueInfactcrackingitisbasicallyimpossible-successfullycalculatingthecorrectstringvalueusingbruteforcemethodsneedsabout2tothe11thtime

Summary

CSRFattacks

Cross-siterequestforgeryalsoknownasCSRFisaverydangerouswebsecuritythreatItisknowninwebsecuritycirclesasasleepinggiantsecurityissueasyoucantellCSRFattackshavequitethereputationThissectionnotonlyintroducedcross-siterequestforgeryitselfbutfactorsunderlyingthisvulnerabilityItconcludeswithsomesuggestionsandmethodsforpreventingsuchattacksIhopethissectionwillhaveinspiredyouasareadertowritebetterandmoresecurewebapplications

LinksDirectoryPrevioussectionSecurityandencryptionNextsectionFilterinputs

CSRFattacks

92FilteringinputsFilteringuserdataisonewaywecanimprovethesecurityofourwebappsusingittoverifythelegitimacyofincomingdataAlloftheinputdataisfilteredinordertoavoidmaliciouscodeordatafrombeingmistakenlyexecutedorstoredMostwebapplicationvulnerabilitiesariseformneglectingtofilterinputdataandnaivelytrustingit

Ourintroductiontofilteringdataisdividedintothreesteps

1 identifyingthedataweneedtofilterthedatatofigureoutwhereitoriginatedfrom2 filteringofthedataitselfweneedtofigureoutwhatkindofdatawehavereceived3 distinguishbetweenfiltered(sanitized)andtainteddataafterthedatahasbeenfilteredwecanbeassuredthatitis

secure

IdentifyingdataIdentifyingthedataisourfirststepbecausemostofthetimeasmentionedwedontknowwhereitoriginatesfromWithoutthisknowledgewewouldbeunabletoproperlyfilteritThedatahereisprovidedinternallyallfromnon-codedataForexamplealldatacomesfromclientshoweverclientsthatareusersarenottheonlyexternalsourcesofdataAdatabaseinterfaceprovidingthirdpartydatacouldalsobeanexternaldatasource

DatathathasbeenenteredbyauserisveryeasytorecognizeinGoWeuserParseFormaftertheuserPOSTsaformtogetallofthedatainsidetherFormOthertypesofinputaremuchhardertoidentifyForexampleinrHeadersmanyoftheelementsareoftenmanipulatedbytheclientItcanoftenbedifficulttoidentifywhichoftheseelementshavebeenmanipulatedbyclientssoitsbesttoconsiderallofthemashavingbeentaintedTherHeaderGet(Accept-Charset)headerfieldforinstanceisalsoconsideredasuserinputalthoughthesearetypicallyonlymanipulatedbybrowsers

FilteringdataIfweknowthesourceofthedatawecanfilteritFilteringisabitofaformaluseofthetermTheprocessisknownbymanyothertermssuchasinputcleaningvalidationandsanitizationDespitethefactthatthesetermsdiffersomewhatintheirmeaningtheyallrefertothesamethingtheprocessofpreventingillegaldatafrommakingitswayintoyourapplications

TherearemanywaystofilterdatasomeofwhicharelesssecurethanothersThebestmethodistocheckwhetherornotthedataitselfmeetsthelegalrequirementsdictatedbyyourapplicationWhenattemptingtodosoitsveryimportantnottomakeanyattemptsatcorrectingtheillegaldatathiscouldallowmalicioususerstomanipulateyourvalidationrulesfortheirownneedsaltogetherdefeatingthepurposeoffilteringthedatainthefirstplaceHistoryhasproventhatattemptingtocorrectinvaliddataoftenleadstosecurityvulnerabilitiesLetstakealookatanoverlysimpleexampleforillustrationpurposesSupposethatabankingsystemasksuserstosupplyasecure6digitpasswordThesystemvalidatesthelengthofallpasswordsOnemightnaivelywriteavalidationrulethatcorrectspasswordsofillegallengthsIfapasswordisshorterthanthelegallengthfillintheremainingdigitswith0sThissimplerulewouldallowattackerstoguessjustthefirstfewdigitsofapasswordtosuccessfullygainaccesstouseraccounts

Wecanuseseverallibrariestohelpustofilterdata

ThestrconvpackagecanhelpustoconvertstringsinputbyusersintospecifictypessincerFormsaremapsofstringvaluesSomecommonstringconversionsprovidedbystrconvareAtoiParseBoolParseFloatandParseIntGosstringspackagecontainssomefilterfunctionslikeTrimToLowerandToTitlewhichcanhelpustoobtaindatainaspecificformatsaccordingtoourneedsGosregexppackagecanbeusedtohandlecaseswhicharemorecomplexinnaturesuchasdeterminingwhetheraninputisanemailaddressabirthdayetc

Filterinputs

FilteringincomingdatainadditiontoauthenticationcanbequiteeffectiveLetsaddanothertechniquetoourrepertoirecalledwhitelistingWhitelistingisagoodwayofconfirmingthelegitimacyofincomingdataUsingthismethodifanerroroccursitcanonlymeanthattheincomingdataisillegalandnottheoppositeOfcoursewedontwanttomakeanymistakesinourwhitelistbyfalselylabellinglegitimatedataasillegalbutthisscenarioismuchbetterthanillegaldatabeinglabeledaslegitimateandthusmuchmoresecure

DistinguishingbetweenfilteredandtainteddataIfyouhavecompletedtheabovestepsthejoboffilteringdatahasbasicallybeencompletedHoweverwhenwritingwebapplicationswealsoneedtodistinguishbetweenfilteredandtainteddatabecausedoingsocanguaranteetheintegrityofourdatafilteringprocesswithoutaffectingtheinputdataLetsputallofourfiltereddataintoaglobalmapvariablecalledCleanMapThentwoimportantstepsarerequiredtopreventcontaminationviadatainjection

EachrequestmustinitializeCleanMapasanemptymapPreventvariablesfromexternaldatasourcesnamedCleanMapfrombeingintroducedintotheapp

Nextletsuseanexampleformtoreinforcetheseconcepts

ltformaction=whoamimethod=POSTgt

WhoamI

ltselectname=namegt

ltoptionvalue=astaxiegtastaxieltoptiongt

ltoptionvalue=herrygtherryltoptiongt

ltoptionvalue=marrygtmarryltoptiongt

ltselectgt

ltinputtype=submitgt

ltformgt

IndealingwiththistypeofformitcanbeveryeasytomakethemistakeofthinkingthatuserswillonlybeabletosubmitoneofthethreeselectoptionsInfactPOSToperationscaneasilybesimulatedbyattackersForexamplebysubmittingthesameformwithname=attackamalicioususercouldintroduceillegaldataintooursystemWecanuseasimplewhitelisttocounterthesetypesofattacks

rParseForm()

name=rFormGet(name)

CleanMap=make(map[string]interface0)

ifname==astaxie||name==herry||name==marry

CleanMap[name]=name

TheabovecodeinitializesaCleanMapvariableandanameisonlyassignedaftercheckingitagainstaninternalwhitelistoflegitimatevalues(astaxieherryandmarryinthiscase)WestorethedataintheCleanMapinstancesoyoucanbesurethatCleanMap[name]holdsavalidatedvalueAnycodewishingtoaccessthisvaluecanthenfreelydosoWecanalsoaddanadditionalelsestatementtotheaboveifwhitelistfordealingwithillegaldataapossibilitybeingthattheformwasdisplayedwithanerrorDonottrytobetooaccommodatingthoughoryouruntheriskofaccidentallycontaminatingyourCleanMap

TheabovemethodforfilteringdataagainstasetofknownlegitimatevaluesisveryeffectiveThereisanothermethodforcheckingwhetherornotincomingdataconsistsoflegalcharactersusingregexphoweverthiswouldbeineffectualintheabovecasewherewerequirethatthenamebeanoptionfromtheselectForexampleyoumayrequirethatusernamesonlyconsistoflettersandnumbers

rParseForm()

username=rFormGet(username)

ifok_=regexpMatchString(^[a-zA-Z0-9]$username)ok

CleanMap[username]=username

Filterinputs

SummaryDatafilteringplaysavitalroleinthesecurityofmodernwebapplicationsMostsecurityvulnerabilitiesaretheresultofimproperlyfilteringdataorneglectingtoproperlyvalidateitBecausetheprevioussectiondealtwithCSRFattacksandthenexttwowillbeintroducingXSSattacksandSQLinjectiontherewasnonaturalsegueintodealingwithatopicasimportantasdatasanitizationsointhissectionwepaidspecialattentiontoit

LinksDirectoryPrevioussectionCSRFattacksNextsectionXSSattacks

Filterinputs

93XSSattacksWiththedevelopmentofInternettechnologywebapplicationsareoftenpackedwithdynamiccontenttoimproveuserexperienceDynamiccontentiscontentthatreactsandchangesaccordingtouserrequestsandactionsDynamicsitesareoftensusceptibletocross-sitescriptingattacks(oftenreferredtobysecurityexpertsinitsabbreviatedformXSS)somethingwhichstaticwebsitesarecompletelyunaffectedby

WhatisXSSAsmentionedthetermXSSisanacronymforCross-SiteScriptingwhichisatypeofattackcommononthewebInordernottoconfuseitwithanothercommonwebacronymCSS(CascadingStyleSheets)weuseanXinsteadofaCforthecrossincross-sitescriptingXSSisacommonwebsecurityvulnerabilitywhichallowsattackerstoinjectmaliciouscodeintowebpagesUnlikemosttypesofattackswhichgenerallyinvolveonlyanattackerandavictimXSSinvolvesthreepartiesanattackeraclientandawebapplicationThegoalofanXSSattackistostealcookiesstoredonclientsbywebapplicationsforthepurposeofreadingsensitiveclientinformationOnceanattackergetsaholdofthisinformationtheycanimpersonateusersandinteractwithwebsiteswithouttheirknowledgeorapproval

XSSattackscanusuallybedividedintotwocategoriesoneisastoredXSSattackThisformofattackariseswhenusersareallowedtoinputdataontoapublicpagewhichafterbeingsavedbytheserverwillbereturned(unescaped)tootherusersthathappentobebrowsingitSomeexamplesofthetypesofpagesthatareoftenaffectedincludecommentsreviewsblogpostsandmessageboardsTheprocessoftengoeslikethisanattackerenterssomehtmlfollowedbyahiddenltscriptgttagcontainingsomemaliciouscodethenhitssaveThewebapplicationsavesthistothedatabaseWhenanotheruserrequeststhispagetheapplicationqueriesthistainteddatafromthedatabaseandservesthepagetotheuserTheattackersscriptthenexecutesarbitrarycodeontheclientscomputer

TheothertypeisareflectedXSSattackThemainideaistoembedamaliciousscriptdirectlyintothequeryparametersofaURLaddressAserverthatimmediatelyparsesthisdataintoapageofresultsandreturnsit(totheclientwhomadetherequest)unsanitizedcanunwittinglycausetheclientscomputertoexecutethiscodeAnattackercansendauseralegitimatelookinglinktoatrustedwebsitewiththeencodedpayloadclickingonthislinkcancausetheusersbrowsertoexecutethemaliciousscript

XSSpresentthemainmeansandendsasfollows

TheftofcookiesaccesstosensitiveinformationTheuseofembeddedFlashthroughcrossdomainpermissionscanalsobeusedbyanattackertoobtainhigheruserprivilegesThisalsoappliesforothersimilarattackvectorssuchasJavaandVBScriptTheuseofiframesframesXMLHttpRequestsetccanallowanattackertoassumetheidentityofausertoperformadministrativeactionssuchasmicro-bloggingaddingfriendssendingprivatemessagesandotherroutineoperationsAwhileagotheSinamicrobloggingplatformsufferedfromthistypeofXSSvulnerabilityWhenmanyusersvisitapageaffectedbyanXSSattacktheeffectonsomesmallersitescanbecomparabletothatofaDDoSattack

XSSprinciplesWebapplicationsthatreturnrequesteddatatouserswithoutfirstinspectingandfilteringitcanallowmalicioususerstoinjectscripts(typicallyembeddedinsideHTMLwithinltscriptgttags)ontootherusersbrowsersWhenthismaliciouscodeisrenderedonausersbrowserwithoutfirsthavingbeenescapedfromtheusersbrowserwillinterpretthiscodethisisthedefinitionofanXSSattackandthistypeofmistakeistheleadingcauseofXSSvulnerabilities

LetsgothroughtheprocessofareflectiveXSSattackLetssaytheresawebsitethatoutputsausersnameaccordingtotheURLqueryparametersaccessthefollowingURLhttp127001name=astaxiewillcausetheservertooutputthefollowing

XSSattacks

helloastaxie

Letssaywepassthefollowingparameterinsteadaccessingthesameurlhttp127001name=ltscriptgtalert(astaxiexss)ltscriptgtIfthiscausesthebrowsertoproduceanalertpop-upboxwecanconfirmthatthesiteisvulnerabletoXSSattacksSohowdomalicioususersstealcookiesusingthesametypeofattack

JustlikebeforewehaveaURL

http127001

name=amp60scriptamp62documentlocationhref=httpwwwxxxcomcookie+documentcookieamp60scriptamp62

ByclickingonthisURLyoudbesendingthecurrentcookietothespecifiedsitewwwxxxcomYoumightbewonderingwhywouldanybodyclickonsuchastrangelookingURLinthefirstplaceWhileitstruethatthiskindofURLwillmakemostpeopleskepticalifanattackerweretouseoneofthemanypopularURLshorteningservicestoobscureitwouldyoustillbeabletoseeitMostattackerswouldobfuscatetheURLinonewayoranotherandyoudonlyknowthelegitimacyofthelinkafterclickingonitHoweverbythispointcookiedatawillhavealreadybeensenttothe3rdpartywebsitecompromisingyoursensitiveinformationYoucanusetoolslikeWebsleuthtoauditthesecurityofyourwebapplicationsforthesetypesofvulnerabilities

ForamoredetailedanalysisonanXSSattackhavealookatthearticle[SinamicrobloggingXSSeventanalysis](httpwwwrisingcomcnnewsletternews2011-08-189621html)

HowtopreventXSSTheanswerissimplenevertrustuserinputandalwaysfilteroutallspecialcharactersinanyinputdatayoumayreceiveThiswilleliminatethemajorityofXSSattacks

UsethefollowingtechniquestodefendagainstXSSattacks

Filterspecialcharacters

OnewaytoavoidXSSistofilteruser-suppliedcontentTheGolanguageprovidessomeHTMLfilteringfunctionsinitstexttemplatepackgesuchasHTMLEscapeStringandJSEscapeStringtonameafew

SpecifythecontenttypeinyourHTTPheaders

wHeader()Set(Content-Typetextjavascript)

Thisallowsclientbrowserstoparsetheresponseasjavascriptcode(applyingtheneccessaryfilters)insteadofrenderingthecontentinanunspecifiedandpotentiallydangerousmanner

SummaryIntroducingXSSvulnerabilitiesisaveryrealhazardwhendevelopingwebapplicationsItisimportanttoremembertofilteralldataespeciallybeforeoutputtingittoclientsthisisnowawell-establishedmeansofpreventingXSS

LinksDirectoryPrevioussectionFilterinputsNextsectionSQLinjection

XSSattacks

94SQLinjection

WhatisSQLinjectionSQLinjectionattacksare(asthenamewouldsuggest)oneofthemanytypesofscriptinjectionattacksInwebdevelopmentthesearethemostcommonformofsecurityvulnerabilitiesAttackerscanuseittoobtainsensitiveinformationfromdatabasesandaspectsofanattackcaninvolveaddinguserstothedatabaseexportingprivatefilesandevenobtainingthehighestsystemprivilegesfortheirownnefariouspurposes

SQLinjectionoccurswhenwebapplicationsdonoteffectivelyfilteroutuserinputleavingthedoorwideopenforattackerstosubmitmaliciousSQLquerycodetotheserverApplicationsoftenreceiveinjectedcodeaspartofanattackersinputwhichaltersthelogicoftheoriginalqueryinsomewayWhentheapplicationattemptstoexecutethequerytheattackersmaliciouscodeisexecutedinstead

SQLinjectionexamplesManywebdevelopersdonotrealizehowSQLqueriescanbetamperedwithandmayholdthemisconceptionthattheyaretrustedcommandsAseveryoneknowsSQLqueriesareabletocircumventaccesscontrolstherebybypassingthestandardauthenticationandauthorizationchecksWhatsmoreitspossibletorunSQLqueriesthroughcommandsatthelevelofthehostsystem

LetshavealookatsomerealexamplestoexplaintheprocessofSQLinjectionindetail

Considerthefollowingsimpleloginform

ltformaction=loginmethod=POSTgt

ltpgtUsernameltinputtype=textname=usernamegtltpgt

ltpgtPasswordltinputtype=passwordname=passwordgtltpgt

ltpgtltinputtype=submitvalue=Logingtltpgt

ltformgt

Ourformprocessingmightlooklikethis

password=rFormGet(password)

sql=SELECTFROMuserWHEREusername=+username+ANDpassword=+password+

Iftheuserinputsausernameorpasswordas

myuserorfoo=foo--

ThenourSQLbecomesthefollowing

SELECTFROMuserWHEREusername=myuserorfoo=foo--ANDpassword=xxx

InSQLanythingafter--isacommentThusinsertingthe--astheattackerdidabovealtersthequeryinafatalwayallowinganattackertosuccessfullyloginasauserwithoutavalidpassword

FarmoredangerousexploitsexistforMSSQLSQLinjectionsandsomecanevenperformsystemcommandsThefollowingexampleswilldemonstratehowterribleSQLinjectionscanbeinsomeversionsofMSSQLdatabases

sql=SELECTFROMproductsWHEREnameLIKE+prod+

DbExec(sql)

SQLinjection

Ifanattackersubmitsaexecmasterxp_cmdshellnetusertesttestpassADD--astheprodvariablethenthesqlwillbecome

sql=SELECTFROMproductsWHEREnameLIKEaexecmasterxp_cmdshellnetusertesttestpassADD--

TheMSSQLServerexecutestheSQLstatementincludingthecommandsintheusersuppliedprodvariablewhichaddsnewuserstothesystemIfthisprogramisrunasisandtheMSSQLSERVERservicehassufficientprivilegesanattackercanregisterasystemaccounttoaccessthismachine

AlthoughtheexamplesabovearetiedtoaspecificdatabasesystemthisdoesnotmeanthatotherdatabasesystemscannotbesubjectedtosimilartypesofattacksTheprinciplesbehindSQLinjectionattacksremainthesamethoughthemethodwithwhichtheyareperpetratedmayvary

HowtopreventSQLinjectionYoumightbethinkingthatanattackerwouldhavetoknowinformationaboutthetargetdatabasesstructureinordertocarryoutanSQLinjectionattackWhilethisistrueitsdifficulttoguaranteethatanattackerwontbeabletofindthisinformationandoncetheygetitthedatabasecanbecompromisedIfyouareusingopensourcesoftwaretoaccessthedatabasesuchasaforumapplicationintruderscaneasilygettherelatedcodeObviouslywithpoorlydesignedcodethesecurityrisksareevengreaterDiscuzphpwindandphpcmsaresomeexamplesofpopularopensourceprogramsthathavebeenvulnerabletoSQLinjectionattacks

TheseattackshappentosystemswheresafetyprecautionsarenotprioritizedWevesaiditbeforewellsayitagainnevertrustanykindofinputespeciallyuserdataThisincludesdatacomingfromselectionboxeshiddeninputfieldsorcookiesAsourfirstexampleabovehasshownevensupposedlynormalqueriescancausedisasters

SQLinjectionattackscanbedevastating-howcandoweevenbegintodefendagainstthemThefollowingsuggestionsareagoodstartingpointforpreventingSQLinjection

1 Strictlylimitpermissionsfordatabaseoperationssothatusersonlyhavetheminimumsetofpermissionsrequiredtoaccomplishtheirworkthusminimizingtheriskofdatabaseinjectionattacks

2 CheckthatinputdatahastheexpecteddataformatandstrictlylimitthetypesofvariablesthatcanbesubmittedThiscaninvolveregexpmatchingorusingthestrconvpackagetoconvertstringsintootherbasictypesforsanitizationandevaluation

3 Transcodeorescapefrompairsofspecialcharacters(ampetc)beforepersistingthemintothedatabaseGostexttemplatepackagehasaHTMLEscapeStringfunctionthatcanbeusedtoreturnescapedHTML

4 UseyourdatabasesparameterizedqueryinterfaceParameterizedstatementsuseparametersinsteadofconcatenatinguserinputvariablesinembeddedSQLstatementsinotherwordstheydonotdirectlyspliceSQLstatementsForexampleusingthePreparefunctioninGosdatabasesqlpackagewecancreatepreparedstatementsforlaterexecutionwithQueryorExec(querystringargsinterface)

5 BeforereleasingyourapplicationthoroughlytestitusingprofessionaltoolsfordetectingSQLinjectionvulnerabilitiesandtorepairthemiftheyexistTherearemanyonlineopensourcetoolsthatdojustthissuchassqlmapSQLninjatonameafew

6 AvoidprintingoutSQLerrorinformationonpublicwebpagesAttackerscanusetheseerrormessagestocarryoutSQLinjectionattacksExamplesofsucherrorsaretypeerrorsfieldsnotmatchingerrorsoranyerrorscontainingSQLstatements

SummaryThroughtheaboveexampleswevelearnedthatSQLinjectionisaveryrealandverydangerouswebsecurityvulnerabilityWhenwewritewebapplicationweshouldpayattentiontoeverylittledetailandtreatsecurityissueswiththeutmostcareDoingsowillleadtobetterandmoresecurewebapplicationsandcanultimatelybethedetermingfactorinwhetherornotyourapplicationsucceeds

SQLinjection

LinksDirectoryPrevioussectionXSSattacksNextsectionPasswordstorage

SQLinjection

95PasswordstorageOvertheyearsmanywebsiteshavesufferedfrombreachesinuserpassworddataEventopinternetcompaniessuchasLinkedinandCSDNnethavebeenaffectedTheimpactoftheseeventshasbeenfeltacrosstheentireinternetandcannotbeunderestimatedThisisespeciallythecasefortodaysinternetuserswhooftenadoptthehabitofusingthesamepasswordformanydifferentwebsites

AswebdeveloperswehavemanychoiceswhenitcomestoimplementingapasswordstorageschemeHoweverthisfreedomisoftenadoubleedgedswordSowhatarethecommonpitfallsandhowcanweavoidfallingintothem

BadsolutionCurrentlythemostfrequentlyusedpasswordstorageschemeistoone-wayhashplaintextpasswordsbeforestoringthemThemostimportantcharacteristicofone-wayhashingisthatitisnotfeasibletorecovertheoriginaldatagiventhehasheddata-hencetheone-wayinone-wayhashingCommonlyusedcryptographicone-wayhashalgorithmsincludeSHA-256SHA-1MD5andsoon

YoucaneasilyusethethreeaforementionedhashingalgorithmsinGoasfollows

importcryptosha256

h=sha256New()

ioWriteString(hHismoneyistwicetaintedtaintyoursandtaintmine)

fmtPrintf(xhSum(nil))

importcryptosha1

h=sha1New()

importcryptomd5

h=md5New()

ioWriteString(h需要加密的密码)

Therearetwokeyfeaturesofone-wayhashing

1)givenaone-wayhashofapasswordtheresultingsummaryisalwaysuniquelydetermined2)calculationspeedAstechnologyadvancesitonlytakesasecondtocompletebillionsofone-wayhashcalculations

GiventhecombinationoftheabovetwocharacteristicsandtakingintoaccountthefactthatthemajorityofpeopleusesomecombinationofcommonpasswordsanattackercancomputeacombinationofallthecommonpasswordsEventhoughthepasswordsyoustoreinyourdatabasemaybehashvaluesonlyifattackersgainaccesstothisdatabasetheycancomparethestoredhashestotheirprecomputedhashestoobtainthecorrespondingpasswordsThistypeofattackreliesonwhatistypicallycalledarainbowtable

Wecanseethathashinguserdatausingone-wayhashesmaynotbeenoughOnceawebsitesdatabasegetsleakedtheusersoriginalpasswordcouldpotentiallyberevealedtotheworld

GoodsolutionThemethodmentionedabovemayhavebeensecureenoughtothwartmosthackingattemptsafewyearsagosincemostattackerswouldnothavehadthecomputingresourcestocomputelargerainbowtablesHoweverwiththeriseofparallelcomputingcapabilitiesthesetypesofattacksarebecomingmoreandmorefeasible

Passwordstorage

HowdowesecurelystoreapasswordsothatitcannotbedecipheredbyathirdpartygivenreallifelimitationsintimeandmemoryresourcesThesolutionistocalculateahashedpasswordtodeliberatelyincreasetheamountofresourcesandtimeitwouldtaketocrackitWewanttodesignahashsuchthatnobodycouldpossiblyhavetheresourcesrequiredtocomputetherequiredrainbowtable

VerysecuresystemsutilizehashalgorithmsthattakeintoaccountthetimeandresourcesitwouldrequiretocomputeagivenpassworddigestThisallowsustocreatepassworddigeststhatarecomputationallyexpensivetoperformonalargescaleThegreatertheintensityofthecalculationthemoredifficultitwillbeforanattackertopre-computerainbowtables-somuchsothatitmayevenbeinfeasibletotry

InGoitsrecommendedthatyouusethebcryptpackage

Thepackagessourcecodecanbefoundatthefollowinglinkhttpsgithubcomgolangcryptoblobmasterbcryptbcryptgo

Hereisanexamplecodesnippetwhichcanbeusedtohashstoreandvalidateuserpasswords

packagemain

import(

golangorgxcryptobcrypt

funcmain()

userPassword1=someuser-providedpassword

Generatehashtostorefromuserpassword

hasherr=bcryptGenerateFromPassword([]byte(userPassword1)bcryptDefaultCost)

iferr=nil

TODOProperlyhandleerror

logFatal(err)

fmtPrintln(Hashtostorestring(hash))

Storethishashsomewhereeginyourdatabase

Afterawhiletheuserwantstologinandyouneedtocheckthepasswordheentered

hashFromDatabase=hash

Comparingthepasswordwiththehash

iferr=bcryptCompareHashAndPassword(hashFromDatabase[]byte(userPassword2))err=nil

logFatal(err)

fmtPrintln(Passwordwascorrect)

SummaryIfyoureworriedaboutthesecurityofyouronlinelifeyoucantakethefollowingsteps

1)AsaregularinternetuserwerecommendusingLastPassforpasswordstorageandgenerationondifferentsitesusedifferentpasswords

2)AsaGowebdeveloperwestronglysuggestthatyouuseoneoftheprofessionalwelltestedmethodsaboveforstoringuserpasswords

LinksDirectory

Passwordstorage

PrevioussectionSQLinjectionNextsectionEncryptanddecryptdata

Passwordstorage

96EncryptinganddecryptingdataTheprevioussectiondescribeshowtosecurelystorepasswordsbutsometimesitmightbeneccessarytomodifysomesensitiveencrypteddatathathasalreadybeenstoredintoourdatabaseWhendatadecryptionisrequiredweshoulduseasymmetricencryptionalgorithminsteadoftheone-wayhashingtechniqueswevepreviouslycovered

AdvancedencryptionanddecryptionTheGolanguagesupportssymmetricencryptionalgorithmsinitscryptopackageDonotuseanythingexceptAESinGCMmodeifyoudontknowwhatyouredoing

cryptoaespackageAES(AdvancedEncryptionStandard)alsoknownasRijndaelencryptionmethodisusedbytheUSfederalgovernmentasablockencryptionstandard

InthefollowingexamplewedemonstratehowtoencryptdatausingAESinGCMmode

packagemain

import(

cryptoaes

cryptocipher

cryptorand

errors

funcmain()

text=[]byte(MynameisAstaxie)

key=[]byte(the-key-has-to-be-32-bytes-long)

ciphertexterr=encrypt(textkey)

iferr=nil

logFatal(err)

fmtPrintf(s=gtxntextciphertext)

plaintexterr=decrypt(ciphertextkey)

iferr=nil

logFatal(err)

fmtPrintf(x=gtsnciphertextplaintext)

funcencrypt(plaintext[]bytekey[]byte)([]byteerror)

cerr=aesNewCipher(key)

iferr=nil

returnnilerr

gcmerr=cipherNewGCM(c)

iferr=nil

returnnilerr

nonce=make([]bytegcmNonceSize())

if_err=ioReadFull(randReadernonce)err=nil

returnnilerr

returngcmSeal(noncenonceplaintextnil)nil

funcdecrypt(ciphertext[]bytekey[]byte)([]byteerror)

iferr=nil

returnnilerr

iferr=nil

returnnilerr

nonceSize=gcmNonceSize()

iflen(ciphertext)ltnonceSize

returnnilerrorsNew(ciphertexttooshort)

nonceciphertext=ciphertext[nonceSize]ciphertext[nonceSize]

returngcmOpen(nilnonceciphertextnil)

CallingtheabovefunctionaesNewCipher(whose[]bytekeyparametermustbe1624or32correspondingtotheAES-128AES-192orAES-256algorithmsrespectively)returnsacipherBlockInterfacethatimplementsthreefunctions

typeBlockinterface

BlockSizereturnstheciphersblocksize

BlockSize()int

Encryptencryptsthefirstblockinsrcintodst

Dstandsrcmaypointatthesamememory

Encrypt(dstsrc[]byte)

Decryptdecryptsthefirstblockinsrcintodst

Decrypt(dstsrc[]byte)

ThesethreefunctionsimplementencryptionanddecryptionoperationsseetheGodocumentationforamoredetailedexplanation

SummaryThissectiondescribesencryptionalgorithmswhichcanbeusedindifferentwaysaccordingtoyourwebapplicationsencryptionanddecryptionneedsForapplicationswithevenbasicsecurityrequirementsitisrecommendedtouseAESinGCMmode

LinksDirectoryPreviousstorepasswordsNextSummary

97SummaryInthischapterwevedescribedCSRFXSSandSQLinjectionbasedattacksMostwebapplicationsarevulnerabletothesetypesofattacksduetoalackofadequateinputfilteringonthepartoftheapplicationSoinadditiontointroducingtheprinciplesbehindtheseattackswevealsointroducedafewtechniquesforeffectivelyfilteringuserdataandpreventingtheseattacksfromevertakingplaceWethendiscussedafewmethodsforsecurelystoringuserpasswordsfirstintroducingbasicone-wayhashingforwebapplicationswithloosesecurityrequirementsthenpasswordsaltingandencryptionalgorithmsformoreseriousapplicationsFinallywebrieflydiscussedtwo-wayhashingandtheencryptionanddecryptionofsensitivedataWelearnedthattheGolanguageprovidespackagesforthreesymmetricencryptionalgorithmsbase64AESandDESThepurposeofthischapteristohelpreadersbecomemoreconsciousofthesecurityissuesthatexistinmoderndaywebapplicationsHopefullyitcanhelpdeveloperstoplananddesigntheirwebapplicationsalittlemorecarefullysotheycanwritesystemsthatareabletopreventhackersfromexploitinguserdataTheGolanguagehasalargeandwelldesignedanti-attacktoolkitandeveryGodevelopershouldtakefulladvantageofthesepackagestobettersecuretheirwebapplications

LinksDirectoryPrevioussectionEncryptanddecryptdataNextchapterInternationalizationandlocalization

Summary

10InternationalizationandlocalizationInordertoadapttotheincreasingglobalizationoftheinternetasdeveloperswemaysometimesneedtobuildmultilingualinternationalwebapplicationsThismeansthatsomepageswillappearindifferentlanguagesaccordingtouserregionsandperhapstheUIandUXwillalsobeadaptedtoshowdifferenteffectsbasedonlocalholidaysorcultureForexampleatruntimetheapplicationwillbeabletorecognizeandprocessrequestscomingfromdifferentgeographicalregionsandrenderpagesinthelocaldialectordisplaydifferentuserinterfaceAscompetentdeveloperswedontwanttohavetomanuallymodifyourapplicationssourcecodetocatertoeverypossibleregionoutthereWhenanapplicationneedstoaddsupportforanewlanguageweshouldbeabletosimplydropintheappropriatelanguagepackandbedonewithit

Inthissectionwellbetalkingaboutinternationalizationandlocalization(usuallyexpressedasi18nandL10Nrespectively)InternationalizationistheprocessofdesigningapplicationsthatareflexibleenoughtobeservedtomultipleregionsaroundtheworldInsomewayswecanthinkofinternationalizationassomethingthathelpstofacilitatelocalizationwhichistheadaptationofawebapplicationscontentanddesigntosuitthelanguageorculturalneedsofspecificlocales

CurrentlyGosstandardpackagedoesnotprovidei18nsupportbuttherearesomeusefulandrelativelysimplethird-partyimplementationsavailableInthischapterwellbeusingtheopen-sourcego-i18nlibrarytosupportinternationalizationinourexamples

WhenwetalkaboutmakingourwebapplicationsinternationalwemeanthateachwebpageshouldbeconstructedwithlocalespecificinformationandassembledwiththecorrespondinglocalstringstimeandcurrencyformatsetcThisinvolvesthreethings

1 howtodeterminetheuserslocale

2 howtosavestringsorotherinformationassociatedwiththelocale

3 howtoembedstringsandotherinformationaccordingtotheuserslocale

InthefirstsectionwelldescribehowtodetectandsetthecorrectlocaleinordertoallowwebsiteusersaccesstotheirlanguagespecificpagesThesecondsectiondescribeshowtohandleorstorestringscurrenciestimesdatesandotherlocalerelatedinformationFinallythethirdsectionwilldescribehowtointernationalizeyourwebapplicationmorespecificallywelldiscusshowtoreturndifferentpageswithlocaleappropriatecontentThroughthesethreesectionswellbeabletosupportfulli18ninourwebapplications

LinksDirectoryPreviousChapterChapter9SummaryNextsectionSettingthedefaultregion

101Settingthedefaultregion

FindingoutthelocaleAlocaleisasetofdescriptorsforaparticulargeographicalregionandcanincludespecificlanguagehabitstextformattingculturalidiomsandamultitudeofothersettingsAlocalesnameisusuallycomposedofthreepartsFirst(andmandatory)isthelocaleslanguageabbreviationsuchasenforEnglishorzhforChineseThesecondpartisanoptionalcountryspecifierandfollowsthefirstwithanminussignThisspecifierallowswebapplicationstodistinguishbetweendifferentcountrieswhichspeakthesamelanguagesuchasen-USforUSEnglishanden-GBforBritishEnglishThelastpartisanotheroptionalspecifierandisaddedtothelocalewithaperiodItspecifieswhichcharactersettouseforinstancezh-CNgb2312specifiesthegb2312charactersetforChinese

GodefaultstotheUTF-8encodingsetsoi18ninGoapplicationsdonotneedtoconsiderthelastparameterThusinourexampleswellonlyusethefirsttwopartsoflocaledescriptionsasourstandardi18nlocalenames

OnLinuxandSolarissystemsyoucanusethelocale-acommandtogetalistofallsupportedregionalnamesYoucanusethislistasexamplesofsomecommonlocalesForBSDandothersystemsthereisnolocalecommandbuttheregionalinformationisstoredinusrsharelocale

SettingthelocaleNowthatwevedefinedwhatalocaleisweneedtobeabletosetitaccordingtovisitingusersinformation(eitherfromtheirpersonalsettingsthevisiteddomainnameetc)Herearesomemethodswecanusetosettheuserslocale

Fromthedomainname

WecansetauserslocaleviathedomainnameitselfwhentheapplicationusesdifferentdomainsfordifferentregionsForexamplewecanusewwwastacomasourdefaultEnglishwebsiteandthedomainnamewwwastacnasitsChinesecounterpartBysettingupseparatedomainsforseparateregionsyoucandetectandservetherequestedlocaleThistypeofsetuphasseveraladvantages

IdentifyingthelocaleviaURLisdistinctiveandunambiguousUsersintuitivelyknowwhichdomainnamestovisitfortheirspecificregionorlanguageImplementingthisschemeinaGoapplicationisverysimpleandconvenientandcanbeachievedthroughamapConducivetosearchenginecrawlerswhichcanimprovethesitesSEO

Wecanusethefollowingcodetoimplementacorrespondingdomainnamelocale

ifrHost==wwwastacom

i18nSetLocale(en)

elseifrHost==wwwastacn

i18nSetLocale(zh-CN)

elseifrHost==wwwastatw

i18nSetLocale(zh-TW)

Alternativelywecouldhavealsosetlocalesthroughtheuseofsub-domainsuchasenastacomforEnglishsitesandcnastacomforChinesesiteThisschemecanberealizedincodeasfollows

Timezone

prefix=stringsSplit(rHost)

ifprefix[0]==en

i18nSetLocale(en)

elseifprefix[0]==cn

elseifprefix[0]==tw

Settinglocalesfromthedomainnameaswevedoneabovehasitsadvantageshoweverl10nisgenerallynotimplementedinthiswayFirstofallthecostofdomainnames(althoughusuallyquiteaffordableindividually)canquicklyaddupgiventhateachlocalewillneeditsowndomainnameandoftenthenameofthedomainwillnotnecessarilyfitinwiththelocalcontextSecondlywedontwanttohavetoindividuallyconfigureeachwebsiteforeachlocaleRatherweshouldbeabletodothisprogrammaticallyforinstancebyusingURLparametersLetshavealookatthefollowingdescription

FromURLparameters

Themostcommonwayofimplementingl10nistosetthedesiredlocaledirectlyintheURLparameterssuchwwwastacomhellolocale=zhorwwwastacomzhhelloThiswaywecansettheregionlikesoi18nSetLocale(params[locale])

ThissetuphasalmostalltheadvantagesofprependingthelocaleinfrontofthedomainanditsRESTfulsowedontneedtoaddadditionalmethodstoimplementitThedownsidetothisapproachisthatitrequiresacorrespondinglocaleparameterinsideeachlinkwhichcanbequitecumbersomeandmayincreasecomplexityHoweverwecanwriteagenericfunctionthatproducestheselocale-specificURLssothatalllinksaregeneratedthroughitThisfunctionshouldautomaticallyaddalocaleparametertoeachlinksowhenusersclickthemweareabletoparsetheirrequestswitheaselocale=params[locale]

PerhapswewantourURLstolookevenmoreRESTfulForexamplewecouldmapeachofourresourcesunderaspecificlocalelikewwwastacomenbooksforourEnglishsiteandwwwastacomzhbooksfortheChineseoneThisapproachisnotonlymoreconducivetoURLSEObutisalsomorefriendlyforusersAnybodyvisitingthesiteshouldbeabletoaccesslocale-specificwebsiteresourcesdirectlyfromtheURLSuchURLaddressescanthenbepassedthroughtheapplicationrouterinordertoobtaintheproperlocale(refertotheRESTsectionwhichdescribestherouterplug-inimplementation)

muxGet(localebookslistbook)

Fromtheclientsettingsarea

InsomespecialcaseswerequireexplicitclientinformationinordertosetthelocaleratherthanobtainingitfromtheURLorURLparametersThisinformationmaycomedirectlyfromtheclientsbrowsersettingstheusersIPaddressorthelocationsettingsfilledoutbytheuseratthetimeofregistrationThisapproachismoresuitableforweb-basedapplications

Accept-Language

WhenaclientrequestsinformationusinganHTTPheadersetwiththeAccept-LanguagefieldwecanusethefollowingGocodetoparsetheheaderandsettheappropriateregioncode

AL=rHeaderGet(Accept-Language)

ifAL==en

i18nSetLocale(en)

elseifAL==zh-CN

elseifAL==zh-TW

Ofcourseinrealworldapplicationswemayrequiremorerigorousprocessesandrulesforsettinguserregions

Timezone

IPAddress

AnotherwayofsettingaclientsregionistolookattheusersIPaddressWecanusethepopularGeoIPGeoLiteCountryorCitylibrariestohelpusrelateuserIPaddressestotheircorrespondingregionalareasImplementingthismechanismisverysimpleweonlyneedtolookuptheusersIPaddressinsideourdatabaseandthenreturnlocale-specificcontentaccordingtowhichregionwasreturned

Userprofile

Youcanalsoletusersprovideyouwiththeirlocaleinformationthroughaninputelementsuchasadrop-downmenu(orsomethingsimilar)WhenwereceivethisinformationwecansaveittotheaccountassociatedwiththeusersprofileWhentheuserlogsinagainwewillbeabletocheckandsettheirlocalesettings-thisguaranteesthateverytimetheuseraccessesthewebsitethereturnedcontentwillbebasedontheirpreviouslysetlocale

SummaryInthissectionwevedemonstratedavarietyofwayswithwhichuserspecificlocalescanbedetectedandsetThesemethodsincludedsettingtheuserlocaleviadomainnamesubdomainnameURLparametersanddirectlyfromclientsettingsBycateringtothespecificneedsofspecificregionswecanprovideacomfortablefamiliarandintuitiveenvironmentforuserstoaccesstheservicesthatweprovide

LinksDirectoryPreviousoneInternationalizationandlocalizationNextsectionLocalizedresources

Timezone

102LocalizedResourcesTheprevioussectiondescribedhowtosetlocalesAfterthelocalehasbeensetwethenneedtoaddresstheproblemofstoringtheinformationcorrespondingtospecificlocalesThisinformationcanincludetextualcontenttimeanddatecurrencyvaluespicturesspecificfilesandotherviewresourcesInGoallofthiscontextualinformationisstoredinJSONformatonourbackendtobecalleduponandinjectedintoourviewswhenusersfromspecificregionsvisitourwebsiteForexampleEnglishandChinesecontentwouldbestoredinenjsonandzh-CNjsonfilesrespectively

LocalizedtextualcontentPlaintextisthemostcommonwayofrepresentinginformationinwebapplicationsandthebulkofyourlocalizedcontentwilllikelytakethisformThegoalistoprovidetextualcontentthatisbothidiomatictoregionalexpressionsandfeelsnaturalforforeignusersofyoursiteOnesolutionistocreateanestedmapoflocalesnativelanguagestringsandtheirlocalcounterpartsWhenclientsrequestpageswithsometextualcontentwefirstchecktheirdesiredlocalethenretrievethecorrespondingstringsfromtheappropriatemapThefollowingsnippetisasimpleexampleofthisprocess

packagemain

importfmt

varlocalesmap[string]map[string]string

funcmain()

locales=make(map[string]map[string]string2)

en=make(map[string]string10)

en[pea]=pea

en[bean]=bean

locales[en]=en

cn=make(map[string]string10)

cn[pea]=豌豆

cn[bean]=毛豆

locales[zh-CN]=cn

lang=zh-CN

fmtPrintln(msg(langpea))

fmtPrintln(msg(langbean))

funcmsg(localekeystring)string

ifvok=locales[locale]ok

ifv2ok=v[key]ok

returnv2

return

Theaboveexamplesetsupmapsoftranslatedstringsfordifferentlocales(inthiscasetheChineseandEnglishlocales)WemapourcntranslationstothesameEnglishlanguagekeyssothatwecanreconstructourEnglishtextmessageinChineseIfwewantedtoswitchourtexttoanyotherlocalewemayhaveimplementeditdbeasimplematterofsettingonelangvariable

Simplekey-valuesubstitutionscansometimesbeinadequateforourneedsForexampleifwehadaphrasesuchasIam30yearsoldwhere30isavariablehowwouldwelocalizeitIncaseslikethesewecancombineusethefmtPrintffunctiontoachievethedesiredresult

en[howold]=Iamdyearsold

cn[howold]=我今年d岁了

fmtPrintf(msg(langhowold)30)

Localizedresources

TheexamplecodeaboveisonlyforthepurposeofdemonstrationactuallocaledataistypicallystoredinJSONformatinourdatabaseallowingustoexecuteasimplejsonUnmarshaltopopulatemaplocaleswithourstringtranslations

LocalizeddateandtimeBecauseofourtimezoneconventionsthetimeinoneregionoftheworldcanbedifferentthanthetimeinanotherregionSimilarlythewayinwhichtimeisrepresentedcanalsovaryfromlocaletolocaleForexampleaChineseenvironmentmayread2012年10月24日星期三23时11分13秒CSTwhileinEnglishitmightbeWedOct24231113CST2012NotonlyaretherevariationsinlanguagebuttherearedifferencesinformattingalsoSowhenitcomestolocalizingdatesandtimesweneedtoaddressthefollowingtwopoints

1 timezones2 formattingissues

The$GOROOTlibtimepackagetimeinfozipdirectorycontainslocalescorrespondingtotimezonedefinitionsInordertoobtainthetimecorrespondingtoauserscurrentlocaleweshouldfirstusetimeLoadLocation(namestring)togetaLocationobjectcorrespondingtoourlocalepassinginastringrepresentingthelocalesuchasAsiaShanghaiorAmericaChicagoWecanthenusethisLocationobjectinconjunctionwithaTimeobject(obtainedbycallingtimeNow)togetthefinaltimeusingtheTimeobjectsInmethodAdetailedlookatthisprocesscanbeseenbelow(thisexampleusessomeofthevariablesfromtheexampleabove)

en[time_zone]=AmericaChicago

cn[time_zone]=AsiaShanghai

loc_=timeLoadLocation(msg(langtime_zone))

t=timeNow()

t=tIn(loc)

fmtPrintln(tFormat(timeRFC3339))

Wecanhandletextformattinginasimilarwaytosolveourtimeformattingproblem

en[date_format]=Y-m-dHMS

cn[date_format]=Y年m月d日H时M分S秒

fmtPrintln(date(msg(langdate_format)t))

funcdate(fomatstringttimeTime)string

yearmonthday=tDate()

hourminsec=tClock()

ParsingthecorrespondingYmdHMSandthenreturningtheinformation

Yreplacedby2012

mreplacedby10

dreplacedby24

LocalizedcurrencyvalueObviouslycurrencydiffersfromregiontoregionalsoWecantreatitthesamewaywetreatedourdates

en[money]=USDd

cn[money]=￥d元

fmtPrintln(date(msg(langdate_format)100))

funcmoney_format(fomatstringmoneyint64)string

returnfmtSprintf(fomatmoney)

Localizedresources

LocalizationofviewsandresourcesWecanservecustomizedviewswithdifferentimagescssjsandotherstaticresourcesdependingonthecurrentlocaleOnewaytoaccomplishthisisbyorganizingthesefilesintotheirrespectivelocalesHeresanexample

|--enEnglishTemplates

|--imagesstorepictureinformation

|--jsJSfiles

|--cssCSSfiles

indextplUserHome

logintplLogHome

|--zh-CNChineseTemplates

|--images

|--css

indextpl

logintpl

Withthisdirectorystructurewecanrenderlocale-specificviewslikeso

s1_=templateParseFiles(views+lang+indextpl)

VVLang=lang

s1Execute(osStdoutVV)

Theresourcesreferencedintheindextplfilecanbedealtwithasfollows

jsfile

ltscripttype=textjavascriptsrc=viewsVVLangjsjqueryjquery-180minjsgtltscriptgt

cssfile

ltlinkhref=viewsVVLangcssbootstrap-responsivemincssrel=stylesheetgt

Picturefiles

ltimgsrc=viewsVVLangimagesbtnpnggt

Withdynamicviewsandthewaywevelocalizedourresourceswewillbeabletoaddmorelocaleswithoutmucheffort

SummaryThissectiondescribedhowtouseandstorelocalresourcesWelearnedthatwecanuseconversionfunctionsandstringinterpolationforthisandsawthatmapscanbeaneffectivewayofstoringlocale-specificdataForthelatterwecouldsimplyextractthecorrespondinglocaleinformationwhenneeded-ifitwastextualcontentwedesiredourmappedtranslationsandidiomscouldbepipeddirectlytotheoutputIfitwassomethingmoresophisticatedliketimeorcurrencywesimplyusedthefmtPrintffunctiontoformatitbefore-handLocalizingourviewsandresourceswastheeasiestcaseandsimplyinvolvedorganizingourfilesintotheirrespectivelocalesthenreferencingthemfromtheirlocalerelativepaths

LinksDirectoryPrevioussectionSettingthedefaultregionNextsectionInternationalsites

Localizedresources

103InternationalsitesTheprevioussectionexplainedhowtodealwithlocalizedresourcesnamelybyusinglocaleconfigurationfilesSowhatcanwedoifweneedtodealwithmultiplelocalizedresourcesliketexttranslationstimesanddatesnumbersetcThissectionwilladdresstheseissuesonebyone

ManagingmultiplelocalepackagesInthedevelopmentofanapplicationoftenthefirstthingyouneedtodoistodecidewhetherornotyouwanttosupportmorethanonelanguageIfyoudodecidetosupportmultiplelanguagesyoullneedtodevelopanorganizationalstructuretofacilitatetheprocessofaddingmorelanguagesinthefutureOnewaywecandothisistoputallourrelatedlocalefilestogetherinaconfiglocalesdirectoryorsomethingofthelikeLetssupposeyouwanttosupportbothChineseandEnglishInthiscaseyoudbeplacingboththeenjsonandzhjsonlocalefilesintotheaforementionedfolderTheircontentswouldprobablylooksomethinglikethefollowing

zhjson

submit提交

create创建

enjson

submitSubmit

createCreate

Wedecidedtousesome3rdpartyGopackagestohelpusinternationalizeourwebapplicationsInthecaseofgo-i18n(Amoreadvancedi18npackagecanbefoundhere)wefirsthavetoregisterourconfiglocalesdirectorytoloadallofourlocalefiles

Tr=i18nNewLocale()

TrLoadPath(configlocales)

ThispackageissimpletouseWecantestthatitworkslikeso

fmtPrintln(TrTranslate(submit))

Outputsubmit

TrSetLocale(zn)

Outputs递交

AutomaticallyloadlocalpackageWevejustdescribedhowtoautomaticallyloadcustomlanguagepacksInfactthego-i18nlibrarycomespre-loadedwithabunchofdefaultformattinginformationsuchastimeandcurrencyformatsThesedefaultconfigurationscanbeoverriddenandcustomizedbyuserstosuittheirneedsConsiderthefollowingprocess

Internationalsites

Loadthedefaultconfigurationfileswhichareplacedbelowin`go-i18nlocales`

Fileshouldbenamedzhjsonen-jsonen-USjsonetcsowecancontinuouslysupportmorelanguages

func(ilIL)loadDefaultTranslations(dirPathstring)error

direrr=osOpen(dirPath)

iferr=nil

returnerr

deferdirClose()

nameserr=dirReaddirnames(-1)

iferr=nil

returnerr

for_name=rangenames

fullPath=pathJoin(dirPathname)

fierr=osStat(fullPath)

iferr=nil

returnerr

iffiIsDir()

iferr=illoadTranslations(fullPath)err=nil

returnerr

elseiflocale=ilmatchingLocaleFromFileName(name)locale=

fileerr=osOpen(fullPath)

iferr=nil

returnerr

deferfileClose()

iferr=illoadTranslation(filelocale)err=nil

returnerr

returnnil

Usingtheabovecodetoloadallofourdefaulttranslationswecanthenusethefollowingcodetoselectandusealocale

fmtPrintln(TrTime(timeNow()))

Output2009年1月08日星期四203758CST

fmtPrintln(TrTime(timeNow()long))

Output2009年1月08日

fmtPrintln(TrMoney(1111))

Outputyen1111

TemplatemapfuncAbovewevepresentedonewayofmanagingandintegratinganumberoflanguagepacksSomeofthefunctionsweveimplementedarebasedonthelogicallayerforexampleTrTranslateTrTimeTrMoneyandsoonInthelogicallayerwecanusethesefunctions(aftersupplyingtherequiredparameters)forapplyingyourtranslationsoutputtingtheresultsdirectlytothetemplatelayeratrendertimeWhatcanwedoifwewanttousethesefunctionsdirectlyinthetemplatelayerIncaseyouveforgottenearlierinthebookwementionedthatGotemplatessupportcustomtemplatefunctionsThefollowingcodeshowshoweasymapfuncistoimplement

1textinformation

Internationalsites

AsimpletextconversionfunctionimplementingamapfunccanbeseenbelowItusesTrTranslatetoperformtheappropriatetranslations

funcI18nT(argsinterface)string

ok=false

varsstring

iflen(args)==1

sok=args[0](string)

s=fmtSprint(args)

returnTrTranslate(s)

Weregisterthefunctionlikeso

tFuncs(templateFuncMapTI18nT)

Thenuseitfromyourtemplate

VSubmit|T

1 Thedateandtime

DatesandtimescalltheTrTimefunctiontoperformtheirtranslationsThemapfuncisimplementedasfollows

funcI18nTimeDate(argsinterface)string

ok=false

varsstring

iflen(args)==1

sok=args[0](string)

s=fmtSprint(args)

returnTrTime(s)

Registerthefunctionlikeso

tFuncs(templateFuncMapTDI18nTimeDate)

VNow|TD

3CurrencyInformation

CurrenciesusetheTrMoneyfunctiontoconvertmoneyThemapFuncisimplementedasfollows

Internationalsites

funcI18nMoney(argsinterface)string

ok=false

varsstring

iflen(args)==1

sok=args[0](string)

s=fmtSprint(args)

returnTrMoney(s)

tFuncs(templateFuncMapMI18nMoney)

VMoney|M

SummaryInthissectionwelearnedhowtoimplementmultiplelanguagepacksinourwebapplicationsWesawthatthroughcustomlanguagepackswecannotonlyeasilyinternationalizeourapplicationsbutfacilitatetheadditionofotherlanguagesalso(throughtheuseofaconfigurationfile)Bydefaultthego-i18npackagewillprovidesomecommonconfigurationsfortimecurrencyetcwhichcanbeveryconvenienttouseWelearnedthatthesefunctionscanalsobeuseddirectlyfromourtemplatesusingmappingfunctionseachtranslatedstringcanbepipeddirectlytoourtemplatesThisenablesourwebapplicationstoaccommodatemultiplelanguageswithminimaleffort

LinksDirectoryPrevioussectionLocalizedresourcesNextsectionSummary

Internationalsites

104SummaryThroughthisintroductorychapteroni18nyoushouldnowbefamiliarwithsomeofthestepsandprocessesthatarenecessaryforinternationalizingandlocalizingyourwebsitesIvealsointroducedanopensourcesolutionfori18ninGogo-i18nUsingthisopensourcelibrarywecaneasilyimplementmulti-languageversionsofourwebapplicationsThisallowsourapplicationstobeflexibleandresponsivetolocalaudiencesallaroundtheworldIfyoufindanerrorinthisopensourcelibraryoranymissingfeaturespleaseopenanissueorapullrequestLetsstrivetomakeitoneofGosstandardlibraries

LinksDirectoryPrevioussectionInternationalsitesNextchapterErrorhandlingdebuggingandtesting

Summary

11ErrorHandlingDebuggingandTestingWeoftenseethemajorityofaprogrammersprogrammingtimespentoncheckingforbugsandworkingonbugfixesWhetheryouarerefactoringcodeorre-configuringsystemsmuchofyourtimewillundoubtedlybespenttroubleshootingandtestingFromtheoutsidepeoplemaythinkthatallwedoasprogrammersisdesignoursystemsandthenwriteourcodeTheymightthinkthatwehavetheidealjobWedoworkthatisveryengagingandimplementsystemsthathaveneverbeendonebeforeWhilethislastpartmaybetruewhattheydontknowisthatwespendthemajorityofourtimecyclingbetweentroubleshootingdebuggingandtestingourcodeOfcourseifyouhavegoodprogramminghabitsandthetechnologicalsolutionstohelpyoutakeonthesetasksthenyoucanminimizethetimespentdoingthesethingsenablingyoutofocusinsteadonmorevaluablethingsliketheapplicationlogic

UnfortunatelymanyprogrammersarenotthoroughinfulfillingtheirerrorhandlingdebuggingandtestingresponsibilitiesbeforehandInexperiencedprogrammerswilloftenonlymakeanefforttofinderrorsandflawsaftertheyhaveoccurredspendinghourslocatingandfixingproblemsaftertheapplicationisalreadyonlineItsgoodpractice(andprobablycommonsense)thatweshoulddesignourapplicationswithpropererrorhandlingtestcasesetcfromthegetgoThiswillmakeyourjobandthejobsofalltheotherdeveloperswhomaybeworkingonyourapplicationsomedaymucheasierwhentheyinevitablyneedtomodifythecodeorupgradethesystem

IntheprocessofdevelopingwebapplicationsyouwillinevitablyencounterunforeseenerrorsWhatsthemostefficientwayoffindingthecausesoftheseerrorsandsolvingthemSection111describeshowtohandleerrorsintheGolanguageaswellashowtodesignyourownerrorhandlingpackageandfunctionsSection112describeshowtouseGDBtodebugprogramsunderdynamicoperatingconditionsdependingonavarietyofvariableinformationWethendiscussapplicationmonitoringanddebuggingoperations

Section113willexplainunittestinginGoandfeaturesomein-depthdiscussionsandexamplesonhowtowriteunittestsaswellasdefiningGosunittestingrulesWellseehowfollowingtheseruleswillensurethatwhenupgradingormodifyingyourapplicationthetestcodewillbeabletorunsmoothly

ManyprogrammersavoidspendingtimetolearnandcultivategooddebuggingandtestinghabitsThischaptertakesontheseissueshead-onsoyouwonthavetorunawayfromthesetasksanylongerSinceyourejustlearninghowtobuildwebapplicationsinGoletsusethisopportunitytoestablishthesegoodhabitsfromtheverybeginning

LinksDirectoryPreviouschapterChapter10summaryNextsectionErrorhandling

111ErrorhandlingGosmajordesignconsiderationsarerootedinthefollowingideasasimpleclearandconcisesyntax(similartoC)andstatementswhichareexplicitanddontcontainanyhiddenorunexpectedthingsGoserrorhandlingschemereflectsalloftheseprinciplesinthewaythatitsimplementedIfyourefamiliarwiththeClanguageyoullknowthatitscommontoreturn-1orNULLvaluestoindicatethatanerrorhasoccurredHoweveruserswhoarenotfamiliarwithCsAPIwillnotknowexactlywhatthesereturnvaluesmeanInCitsnotexplicitwhetheravalueof0indicatessuccessoffailureOntheotherhandGoexplicitlydefinesatypecallederrorforthesolepurposeofexpressingerrorsWheneverafunctionreturnswechecktoseewhethertheerrorvariableisnilornottodetermineiftheoperationwassuccessfulForexampletheosOpenfunctionfailsitwillreturnanon-nilerrorvariable

funcOpen(namestring)(fileFileerrerror)

HeresanexampleofhowwedhandleanerrorinosOpenFirstweattempttoopenafileWhenthefunctionreturnswechecktoseewhetheritsucceededornotbycomparingtheerrorreturnvaluewithnilcallinglogFataltooutputanerrormessageifitsanon-nilvalue

ferr=osOpen(filenameext)

iferr=nil

logFatal(err)

SimilartotheosOpenfunctionthefunctionsinGosstandardpackagesallreturnerrorvariablestofacilitateerrorhandlingThissectionwillgointodetailaboutthedesignoferrortypesanddiscusshowtoproperlyhandleerrorsinwebapplications

Errortypeerrorisaninterfacetypewiththefollowingdefinition

typeerrorinterface

Error()string

errorisabuilt-ininterfacetypeWecanfinditsdefinitioninthebuiltinpackagebelowWealsohavealotofinternalpackageswhichuseerrorinaprivatestructurecallederrorStringwhichimplementstheerrorinterface

errorStringisatrivialimplementationoferror

typeerrorStringstruct

sstring

func(eerrorString)Error()string

returnes

YoucanconvertaregularstringtoanerrorStringthrougherrorsNewinordertogetanobjectthatsatisfiestheerrorinterfaceItsinternalimplementationisasfollows

Newreturnsanerrorthatformatsasthegiventext

funcNew(textstring)error

returnamperrorStringtext

Errorhandling

ThefollowingexampledemonstrateshowtouseerrorsNew

funcSqrt(ffloat64)(float64error)

ifflt0

return0errorsNew(mathsquarerootofnegativenumber)

implementation

InthefollowingexamplewepassanegativenumbertoourSqrtfunctionCheckingtheerrvariablewecheckwhethertheerrorobjectisnon-nilusingasimplenilcomparisonTheresultofthecomparisonistruesofmtPrintln(thefmtpackagecallstheerrormethodwhendealingwitherrorcalls)iscalledtooutputanerror

ferr=Sqrt(-1)

iferr=nil

fmtPrintln(err)

CustomErrorsThroughtheabovedescriptionweknowthatagoErrorisaninterfaceBydefiningastructthatimplementsthisinterfacewecanimplementtheirerrordefinitionsHeresanexamplefromtheJSONpackage

typeSyntaxErrorstruct

msgstringerrordescription

Offsetint64wheretheerroroccurred

func(eSyntaxError)Error()stringreturnemsg

TheerrorsOffsetfieldwillnotbeprintedatruntimewhensyntaxerrorsoccurbutusingatypeassertionerrortypeyoucanprintthedesirederrormessage

iferr=decDecode(ampval)err=nil

ifserrok=err(jsonSyntaxError)ok

linecol=findLine(fserrOffset)

returnfmtErrorf(sddvfName()linecolerr)

returnerr

ItshouldbenotedthatwhenthefunctionreturnsacustomerrorthereturnvalueissettotherecommendedtypeoferrorratherthanacustomerrortypeBecarefulnottopre-declarevariablesofcustomerrortypesForexample

funcDecode()SyntaxError

errorwhichmayleadtothecallerserr=nilcomparisontoalwaysbetrue

varerrSyntaxErrorpre-declareerrorvariable

ifanerrorcondition

err=ampSyntaxError

returnerrerrorerralwaysequalnon-nilcausescallerserr=nilcomparisontoalwaysbetrue

Seehttpgolangorgdocfaqnil_errorforanindepthexplanation

TheaboveexampleshowshowtoimplementasimplecustomErrortypeButwhatifweneedmoresophisticatederrorhandlingInthiscasewehavetorefertothenetpackageapproach

Errorhandling

packagenet

typeErrorinterface

Timeout()boolIstheerroratimeout

Temporary()boolIstheerrortemporary

UsingtypeassertionwecancheckwhetherornotourerrorisoftypenetErrorasshowninthefollowingexampleThisallowsustorefineourerrorhandling-ifatemporaryerroroccursonthenetworkitwillsleepfor1secondthenretrytheoperation

ifnerrok=err(netError)okampampnerrTemporary()

timeSleep(1e9)

continue

iferr=nil

logFatal(err)

ErrorhandlingGohandleserrorsandchecksthereturnvaluesoffunctionsinaC-likefashionwhichisdifferenttohowmostoftheothermajorlanguagesdoThismakesthecodemoreexplicitandpredictablebutalsomoreverboseToreducetheredundancyofourerror-handlingcodewecanuseabstracterrorhandlingfunctionsthatallowustoimplementsimilarerrorhandlingbehaviour

funcinit()

httpHandleFunc(viewviewRecord)

funcviewRecord(whttpResponseWriterrhttpRequest)

c=appengineNewContext(r)

key=datastoreNewKey(cRecordrFormValue(id)0nil)

record=new(Record)

iferr=datastoreGet(ckeyrecord)err=nil

httpError(werrError()500)

return

iferr=viewTemplateExecute(wrecord)err=nil

TheaboveexampledemonstratehowthedataaccessandtemplatecallhasdetectedanerrorWhenanerroroccursacalltounifiedhandlerhttpErrorreturnsa500errorcodetotheclientanddisplaysthecorrespondingerrordataButwhenmoreandmoreHandleFunccallsaremadesoerror-handlinglogiccodewillincreaseWecancustomizetheroutertoreducecode(refertothethirdchapterofHTTPformoredetail)

typeappHandlerfunc(httpResponseWriterhttpRequest)error

func(fnappHandler)ServeHTTP(whttpResponseWriterrhttpRequest)

iferr=fn(wr)err=nil

AbovewevedefinedacustomrouterWecanthenregisterourhandlerasusual

Errorhandling

funcinit()

httpHandle(viewappHandler(viewRecord))

Theviewhandlercanthenbehandledbythefollowingcodeitisalotsimplerthanouroriginalimplementationisntit

funcviewRecord(whttpResponseWriterrhttpRequest)error

record=new(Record)

returnerr

returnviewTemplateExecute(wrecord)

Theerrorhandlerexampleabovewillreturnthe500InternalErrorcodetouserswhenanyerrorsoccurinadditiontoprintingoutthecorrespondingerrorcodeInfactwecancustomizethetypeoferrorreturnedtooutputamoredeveloperfriendlyerrormessagewithinformationthatisusefulfordebugginglikeso

typeappErrorstruct

Errorerror

Messagestring

Codeint

Ourcustomroutercanbechangedaccordingly

typeappHandlerfunc(httpResponseWriterhttpRequest)appError

ife=fn(wr)e=nileisappErrornotosError

cErrorf(veError)

httpError(weMessageeCode)

Afterwevefinishedmodifyingourcustomerrorourlogiccanbechangedasfollows

funcviewRecord(whttpResponseWriterrhttpRequest)appError

record=new(Record)

returnampappErrorerrRecordnotfound404

returnampappErrorerrCantdisplayrecord500

returnnil

AsshownabovewecanreturndifferenterrorcodesanderrormessagesinourviewsdependingonthesituationAlthoughthisversionofourcodefunctionssimilarlytothepreviousversionitsmoreexplicitanditserrormessagepromptsaremorecomprehensibleAllofthesefactorscanhelptomakeyourapplicationmorescalableascomplexityincreases

Summary

Errorhandling

FaulttoleranceisaveryimportantaspectofanyprogramminglanguageInGoitisachievedthrougherrorhandlingAlthoughErrorisonlyoneinterfaceitcanhavemanyvariationsinthewaythatitsimplementedandwecancustomizeitaccordingtoourneedsonacasebycasebasisByintroducingthesevariouserrorhandlingconceptswehopethatyouwillhavegainedsomeinsightonhowtoimplementbettererrorhandlingschemesinyourownwebapplications

LinksDirectoryPrevioussectionErrorhandlingdebuggingandtestingNextsectionDebuggingbyusingGDB

Errorhandling

112DebuggingwithGDBDuringthedevelopmentprocessofanyapplicationdeveloperswillalwaysneedtoperformsomekindofcodedebuggingPHPPythonandmostoftheotherdynamiclanguagesareabletobemodifiedatruntimeaslongasthemodificationsdonotexplicitlyneedtobecompiledWecaneasilyprintdataindynamicoperatingenvironmentsoutputtingourchangesandprintingvariableinformationdirectlyInGoyoucanofcoursespeckleyourcodewithPrintlnsbefore-handtodisplayvariableinformationfordebuggingpurposesbutanychangestoyourcodeneedtoberecompiledeverytimeThiscanquicklybecomecumbersomeIfyouveprogrammedinPythonorJavascriptyoullknowthattheformerprovidestoolssuchaspdbandipdbfordebuggingandthelatterhassimilartoolsthatareabletodynamicallydisplayvariableinformationandfacilitatesingle-stepdebuggingFortunatelyGohasnativesupportforasimilartoolwhichprovidessuchdebuggingfeaturesGDBThissectionservesasabriefintroductionintodebuggingGoapplicationsusingGDB

GDBdebuggingprofileGDBisapowerfuldebuggingtooltargetingUNIX-likesystemsreleasedbytheFSF(FreeSoftwareFoundation)GDBallowsustodothefollowingthings

1 Initialsettingscanbecustomizeaccordingtothespecificrequirementsofyourapplication2 Canbesetsothattheprogrambeingdebuggedinthedevelopersconsolestopsattheprescribedbreakpoints

(breakpointscanbeconditionalexpressions)3 Whentheprogramhasbeenstoppedyoucancheckitscurrentstatetoseewhathappened4 Dynamicallychangethecurrentprogramsexecutionenvironment

TodebugyourGoapplicationsusingGDBtheversionofGDByouusemustbegreaterthan71

WhencompilingGoprogramsthefollowingpointsrequireparticularattention

1 Using-ldflags-swillpreventthestandarddebugginginformationfrombeingprinted2 Using-gcflags-N-lwillpreventGofromperformingsomeofitsautomatedoptimizations-optimizationsof

aggregatevariablesfunctionsetcTheseoptimizationscanmakeitverydifficultforGDBtodoitsjobsoitsbesttodisablethematcompiletimeusingtheseflags

SomeofGDBsmostcommonlyusedcommandsareasfollows

AlsousedinitsabbreviatedformllistisusedtodisplaythesourcecodeBydefaultitdisplaystenlinesofcodeandyoucanspecifythelineyouwishtodisplayForexamplethecommandlist15displaystenlinesofcodecenteredaroundline15asshownbelow

10timeSleep(2timeSecond)

11clt-i

13close(c)

16funcmain()

17msg=Startingmain

18fmtPrintln(msg)

19bus=make(chanint)

AlsousedinitsabbreviatedformbbreakisusedtosetbreakpointsandtakesasanargumentthatdefineswhichpointtosetthebreakpointatForexampleb10setsabreakpointatthetenthrow

delete

DebuggingbyusingGDB

AlsousedinitsabbreviatedformddeleteisusedtodeletebreakpointsThebreakpointissetfollowedbytheserialnumberTheserialnumbercanbeobtainedthroughtheinfobreakpointscommandBreakpointssetwiththeircorrespondingserialnumbersaredisplayedasfollowstosetabreakpointnumber

NumTypeDispEnbAddressWhat

2breakpointkeepy0x0000000000400dc3inmainmainathomexiemengjungdbgo23

breakpointalreadyhit1time

backtrace

Abbreviatedasbtthiscommandisusedtoprinttheexecutionofthecodeforinstance

0mainmain()athomexiemengjungdbgo23

10x000000000040d61einruntimemain()athomexiemengjungosrcpkgruntimeprocc244

20x000000000040d6c1inschedunlock()athomexiemengjungosrcpkgruntimeprocc267

30x0000000000000000in()

TheinfocommandcanbeusedinconjunctionwithseveralparameterstodisplayinformationThefollowingparametersarecommonlyused

infolocals

Displaysthecurrentlyexecutingprogramsvariablevalues

infobreakpoints

Displaysalistofcurrentlysetbreakpoints

infogoroutines

Displaysthecurrentlistofrunninggoroutinesasshowninthefollowingcodewiththeindicatingthecurrentexecution

1runningruntimegosched

2syscallruntimeentersyscall

3waitingruntimegosched

4runnableruntimegosched

AbbreviatedaspthiscommandisusedtoprintvariablesorotherinformationIttakesasargumentsthevariablenamestobeprintedandofcoursetherearesomeveryusefulfunctionssuchas$len()and$cap()thatcanbeusedtoreturnthelengthorcapacityofthecurrentstringsslicesormaps

whatis

whatisisusedtodisplaythecurrentvariabletypefollowedbythevariablenameForinstancewhatismsgwilloutputthefollowing

type=structstring

Abbreviatedasnnextisusedinsingle-stepdebuggingtoskiptothenextstepWhenthereisabreakpointyoucanenterntojumptothenextsteptocontinue

continue

AbbreviatedasccontinueisusedtojumpoutofthecurrentbreakpointandcanbefollowedbyaparameterNwhichspecifiesthenumberoftimestoskipthebreakpoint

setvariable

DebuggingbyusingGDB

ThiscommandisusedtochangethevalueofavariableintheprocessItcanbeusedlikesosetvariableltvargt=ltvaluegt

ThedebuggingprocessNowletstakealookatthefollowingcodetoseehowGDBistypicallyusedtodebugGoprograms

packagemain

import(

funccounting(cchanlt-int)

fori=0ilt10i++

timeSleep(2timeSecond)

close(c)

funcmain()

msg=Startingmain

fmtPrintln(msg)

bus=make(chanint)

msg=startingagofunc

gocounting(bus)

forcount=rangebus

fmtPrintln(countcount)

Nowwecompilethefilecreatinganexecutablefilecalledgdbfile

gobuild-gcflags-N-lgdbfilego

UsetheGDBcommandtostartdebugging

gdbgdbfile

AfterfirststartingGDByoullhavetoentertheruncommandtoseeyourprogramrunningYouwillthenseetheprogramoutputthefollowingexecutingtheprogramdirectlyfromthecommandlinewilloutputexactlythesamething

(gdb)run

Startingprogramhomexiemengjungdbfile

Startingmain

count0

count1

count2

count3

count4

count5

count6

count7

count8

count9

[LWP2771exited]

[Inferior1(process2771)exitednormally]

Oknowthatweknowhowtogettheprogramupandrunningletstakealookatsettingbreakpoints

DebuggingbyusingGDB

(gdb)b23

Breakpoint1at0x400d8dfilehomexiemengjungdbfilegoline23

(gdb)run

Startingmain

[NewLWP3284]

[SwitchingtoLWP3284]

Breakpoint1mainmain()athomexiemengjungdbfilego23

23fmtPrintln(countcount)

Intheaboveexampleweusetheb23commandtosetabreakpointonline23ofourcodethenenterruntostarttheprogramWhenourprogramstopsatourbreakpointwetypicallyneedtolookatthecorrespondingsourcecodecontextEnteringthelistcommandintoourGDBsessionwecanseethefivelinesofcodeprecedingourbreakpoint

(gdb)list

18fmtPrintln(msg)

19bus=make(chanint)

20msg=startingagofunc

21gocounting(bus)

22forcount=rangebus

NowthatGDBisrunningthecurrentprogramenvironmentwehaveaccesstosomeusefuldebugginginformationthatwecanprintoutToseethecorrespondingvariabletypesandvaluestypeinfolocals

(gdb)infolocals

count=0

bus=0xf840001a50

(gdb)pcount

(gdb)pbus

$2=(chanint)0xf840001a50

(gdb)whatisbus

type=chanint

Tolettheprogramcontinueitsexecutionuntilthenextbreakpointentertheccommand

(gdb)c

Continuing

count0

[NewLWP3303]

(gdb)c

Continuing

count1

AftereachcthecodewillexecuteoncethenjumptothenextiterationoftheforloopItwillofcoursecontinuetoprintouttheappropriateinformation

LetssaythatyouneedtochangethecontextvariablesinthecurrentexecutionenvironmentskiptheprocessthencontinuetothenextstepYoucandosobyfirstusinginfolocalstogetthevariablestatesthenthesetvariablecommandtomodifythem

DebuggingbyusingGDB

(gdb)infolocals

count=2

bus=0xf840001a50

(gdb)setvariablecount=9

(gdb)infolocals

count=9

bus=0xf840001a50

(gdb)c

Continuing

count9

FinallywhilerunningtheprogramcreatesanumberofgoroutinesWecanseewhateachgoroutineisdoingusinginfogoroutines

(gdb)infogoroutines

(gdb)goroutine1bt

00x000000000040e33binruntimegosched()athomexiemengjungosrcpkgruntimeprocc927

10x0000000000403091inruntimechanrecv(c=voidep=voidselected=voidreceived=void)

athomexiemengjungosrcpkgruntimechanc327

20x000000000040316finruntimechanrecv2(t=voidc=void)

30x0000000000400d6finmainmain()athomexiemengjungdbfilego22

40x000000000040d0c7inruntimemain()athomexiemengjungosrcpkgruntimeprocc244

50x000000000040d16ainschedunlock()athomexiemengjungosrcpkgruntimeprocc267

60x0000000000000000in()

FromthegoroutinescommandwecanhaveabetterpictureofwhatGosruntimesystemisdoinginternallythecallingsequenceforeachfunctionisplainlydisplayed

SummaryInthissectionweintroducedsomebasiccommandsfromtheGDBdebuggerthatyoucanusetodebugyourGoapplicationsTheseincludedtherunprintinfosetvariablecontinuelistandbreakcommandsamongothersFromthebriefexamplesaboveIhopethatyouwillhaveabetterunderstandingofhowthedebuggingprocessworksinGousingtheGDBdebuggerIfyouwanttogetmoredebuggingtipspleaserefertotheGDBmanualonitsofficialwebsite

LinksDirectoryPrevioussectionErrorhandlingNextsectionWritetestcases

DebuggingbyusingGDB

113WritingtestcasesInthecourseofdevelopmentaveryimportantstepistotestourcodetoensureitsqualityandintegrityWeneedtomakesurethateveryfunctionreturnstheexpectedresultandthatourcodeperformsoptimallyWealreadyknowthatthefocusofunittestsistofindlogicalerrorsinthedesignorimplementationofprogramsTheyareusedtodetectandexposeproblemsincodeearlyonsothatwecanmoreeasilyfixthembeforetheygetoutofhandWealsoknowthatperformancetestsareconductedforthepurposeofoptimizingourcodesothatitisstableunderloadandcanmaintainahighlevelofconcurrencyInthissectionwelltakealookatsomecommonlyaskedquestionsabouthowunitandperformancetestsareimplementedinGo

TheGolanguagecomeswithalightweighttestingframeworkcalledtestingandwecanusethegotestcommandtoexecuteunitandperformancetestsGostestingframeworkworkssimilarlytotestingframeworksinotherlanguagesYoucandevelopallsortsoftestsuiteswiththemwhichmayincludetestsforunittestesbenchmarkingstresstestsetcLetslearnabouttestinginGostepbystep

HowtowritetestcasesSincethegotestcommandcanonlybeexecutedinadirectorycontainingallcorrespondingfileswearegoingtocreateanewprojectdirectorygotestsothatallofourcodeandtestcodeareinthesamedirectory

Letsgoaheadandcreatetwofilesinthedirectorycalledgotestgoandgotest_testgo

1 GotestgoThisfiledeclaresourpackagenameandhasafunctionthatperformsadivisionoperation

packagegotest

import(

errors

funcDivision(abfloat64)(float64error)

ifb==0

return0errorsNew(Divisorcannotbe0)

returnabnil

2 Gotest_testgoThisisourunittestfileKeepinmindthefollowingprinciplesfortestfiles

3 Filenamesmustendin_testgosothatgotestcanfindandexecutetheappropriatecode

4 Youhavetoimportthetestingpackage5 AlltestcasefunctionsbeginwithTest6 Testcasesfollowthesourcecodeorder7 TestfunctionsoftheformTestXxx()takeatestingTargumentwecanusethistypetorecorderrorsortogetthe

testingstatus8 InfunctionsoftheformfuncTestXxx(ttestingT)theXxxsectioncanbeanyalphanumericcombinationbutthe

firstlettercannotbealowercaseletter[az]ForexampleTestintdivwouldbeaninvalidfunctionname9 BycallingoneoftheErrorErrorfFailNowFatalorFatalIfmethodsoftestingTonourtestingfunctions

wecanfailthetestInadditionwecancalltheLogmethodoftestingTtorecordtheinformationintheerrorlog

Hereisourtestcode

Writetestcases

packagegotest

import(

testing

funcTest_Division_1(ttestingT)

tryaunittestonfunction

ifie=Division(62)i=3||e=nil

Ifitisnotasexpectedthenthetesthasfailed

tError(divisionfunctiontestsdonotpass)

recordtheexpectedinformation

tLog(firsttestpassed)

tError(justdoesnotpass)

Whenexecutinggotestintheprojectdirectoryitwilldisplaythefollowinginformation

---FAILTest_Division_2(000seconds)

gotest_testgo16isnotpassed

exitstatus1

FAILgotest0013s

Wecanseefromthisresultthatthesecondtestfunctiondoesnotpasssincewewroteinadead-endusingtErrorButwhatabouttheperformanceofourfirsttestfunctionBydefaultexecutinggotestdoesnotdisplaytestresultsWeneedtosupplytheverboseargument-vlikegotest-vtodisplaythefollowingoutput

===RUNTest_Division_1

---PASSTest_Division_1(000seconds)

gotest_testgo11firsttestpassed

exitstatus1

FAILgotest0012s

TheaboveoutputshowsindetailtheresultsofourtestWeseethatthetestfunction1Test_Division_1passesandthetestfunction2Test_Division_2failsfinallyconcludingthatourtestsuitedoesnotpassNextwemodifythetestfunction2withthefollowingcode

if_e=Division(60)e==nil

Ifitisnotasexpectedthentheerror

tError(Divisiondidnotworkasexpected)

recordsomeoftheinformationyouexpecttorecord

tLog(onetestpassede)

Weexecutegotest-vonceagainThefollowinginformationshouldnowbedisplayed-thetestsuitehaspassed~

Writetestcases

gotest_testgo20onetestpasseddivisorcannotbe0

okgotest0013s

HowtowritestresstestsStresstestingisusedtodetectfunctionperformanceandbearssomeresemblancetounittesting(whichwewillnotgetintohere)howeverweneedtopayattentiontothefollowingpoints

StresstestsmustfollowthefollowingformatwhereXXXcanbeanyalphanumericcombinationanditsfirstlettercannotbealowercaseletter

funcBenchmarkXXX(btestingB)

BydefaultGotestdoesnotperformfunctionstresstestsIfyouwanttoperformstresstestsyouneedtosettheflag-testbenchwiththeformat-testbench=test_name_regexForinstancetorunallstresstestsinyoursuiteyouwouldrungotest-testbench=

InyourstresstestspleaseremembertousetestingBNanyloopbodiessothatthetestscanberunproperlyAsbeforetestfilenamesmustendin_testgo

Herewecreateastresstestfilecalledwebbench_testgo

packagegotest

import(

testing

funcBenchmark_Division(btestingB)

fori=0iltbNi++usebNforlooping

Division(45)

funcBenchmark_TimeConsumingFunction(btestingB)

bStopTimer()callthefunctiontostopthestresstesttimecount

Dosomeinitializationworksuchasreadingfiledatadatabaseconnectionsandthelike

Sothatourbenchmarksreflecttheperformanceofthefunctionitself

bStartTimer()re-starttime

fori=0iltbNi++

Division(45)

Wethenexecutethegotest-filewebbench_testgo-testbench=commandwhichoutputsthefollowingresults

Benchmark_Division500000000776nsop

Benchmark_TimeConsumingFunction500000000780nsop

okgotest9364s

TheaboveresultsshowthatwedidnotperformanyofourTestXXXunittestfunctionsandinsteadonlyperformedourBenchmarkXXXtests(whichisexactlyasexpected)ThefirstBenchmark_DivisiontestshowsthatourDivision()functionexecuted500milliontimeswithanaverageexecutiontimeof776nsThesecondBenchmark_TimeConsumingFunctionshows

Writetestcases

thatourTmeConsumingFunctionexecuted500milliontimeswithanaverageexecutiontimeof780nsFinallyitoutputsthetotalexecutiontimeofourtestsuite

SummaryFromourbriefencounterwithunitandstresstestinginGowecanseethatthetestingpackageisverylightweightyetpackedwithusefulutilitiesWesawthatwritingunitandstresstestscanbeverysimpleandrunningthemcanbeeveneasierwithGosbuilt-ingotestcommandEverytimewemodifyourcodewecansimplyrungotesttobeginregressiontesting

LinksDirectoryPrevioussectionDebuggingusingGDBNextsectionSummary

Writetestcases

114SummaryOverthecourseofthelastthreesectionsweveintroducedhowtohandleerrorsinGofirstlookingatgooderrorhandlingpracticesanddesignthenlearninghowtousetheGDBdebuggereffectivelyWesawthatwithGDBwecanperformsingle-stepdebuggingviewandmodifyourprogramvariablesduringexecutionandprintouttherelevantprocessinformationFinallywedescribedhowtouseGosbuilt-intestingframeworktowriteunitandstresstestsProperlyusingthisframeworkallowsustoeasilymakeanyfuturechangestoourcodeandperformthenecessaryregressiontestingGoodwebapplicationsmusthavegooderrorhandlingandpartofthatishavingreadableerrorsanderrorhandlingmechanismswhichcanscaleinapredictablemannerUsingthetoolsmentionedaboveaswellaswritinghighqualityandthoroughunitandstresstestswecanhavepeaceofmindknowingthatonceourapplicationsarelivetheycanmaintainoptimalperformanceandrunasexpected

LinksDirectoryPrevioussectionWritetestcasesNextchapterDeploymentandmaintenance

Summary

12DeploymentandmaintenanceSofarwevecoveredthebasicsofdevelopingdebuggingandtestingwebapplicationsinGoAsisoftensaidhoweverthelast10ofdevelopmenttakes90ofthetimeInthischapterwewillbeemphasizingthislast10ofapplicationdevelopmentinordertotrulycraftreliableandhighqualitywebapplicationsInthefirstsectionwewillexaminehowproductionservicesgeneratelogsandtheprocessofloggingitselfThesecondsectionwilldescribedealingwithruntimeerrorsandhowtomanagethemwhentheyoccursothattheimpactonendusersisminimizedInthethirdsectionwetacklethesubjectofdeployingstandaloneGoprogramswhichcanbetrickyatfirstAsyoumightknowGoprogramscannotbewrittenwithdaemonslikeyouwouldwithalanguagesuchasCWelldiscusshowbackgroundprocessesaretypicallymanagedinGoFinallyourfourthandlastsectionwilladdresstheprocessofbackingupandrecoveringapplicationdatainGoWelltakealookatsometechniquesforensuringthatintheeventofacrashwewillbeabletomaintaintheintegrityofourdata

LinksDirectoryPreviouschapterChapter11summaryNextsectionLogs

121LogsWewanttobuildwebapplicationsthatcankeeptrackofeventswhichhaveoccurredthroughoutexecutioncombiningthemallintooneplaceforeasyaccesslateronwhenweinevitablyneedtoperformdebuggingoroptimizationtasksGoprovidesasimplelogpackagewhichwecanusetohelpusimplementsimpleloggingfunctionalityLogscanbeprintedusingGosfmtpackagecalledinsideerrorhandlingfunctionsforgeneralerrorloggingGosstandardpackageonlycontainsbasicfunctionalityforlogginghoweverTherearemanythirdpartyloggingtoolsthatwecanusetosupplementitifyourneedsaremoresophisticated(toolssimilartolog4jandlog4cppifyouveeverhadtodealwithlogginginJavaorC++)Apopularandfullyfeaturedopen-sourceloggingtoolinGoistheseelogloggingframeworkLetstakealookathowwecanuseseelogtoperformlogginginourGoapplications

IntroductiontoseelogSeelogisaloggingframeworkforGothatprovidessomesimplefunctionalityforimplementingloggingtaskssuchasfilteringandformattingItsmainfeaturesareasfollows

DynamicconfigurationviaXMLyoucanloadconfigurationparametersdynamicallywithoutrecompilingyourprogramSupportshotupdatestheabilitytodynamicallychangetheconfigurationwithouttheneedtorestarttheapplicationSupportsmulti-outputstreamsthatcansimultaneouslypipelogoutputtomultiplestreamssuchasafilestreamnetworkflowetcSupportfordifferentlogoutputs

CommandlineoutputFileOutputCachedoutputSupportlogrotateSMTPMail

TheaboveisonlyapartiallistofseelogsfeaturesTofullytakeadvantageofallofseelogsfunctionalityhavealookatitsofficialwikiwhichthoroughlydocumentswhatyoucandowithitLetsseehowweduseseeloginourprojects

Firstinstallseelog

goget-ugithubcomcihubseelog

Thenletswriteasimpleexample

packagemain

importloggithubcomcihubseelog

funcmain()

deferlogFlush()

logInfo(HellofromSeelog)

CompileandruntheprogramIfyouseeaHellofromseeloginyourapplicationlogseeloghasbeensuccessfullyinstalledandisrunningoperatingnormally

CustomlogprocessingwithseelogSeelogsupportscustomlogprocessingThefollowingcodesnippetisbasedontheitscustomlogprocessingpartofitspackage

packagelogs

import(

errors

seeloggithubcomcihubseelog

varLoggerseelogLoggerInterface

funcloadAppConfig()

appConfig=`

ltseelogminlevel=warngt

ltoutputsformatid=commongt

ltrollingfiletype=sizefilename=datalogsrolllogmaxsize=100000maxrolls=5gt

ltfilterlevels=criticalgt

ltfilepath=datalogscriticallogformatid=criticalgt

ltsmtpformatid=criticalemailsenderaddress=astaxiegmailcomsendername=ShortUrlAPIhostname=smtp

gmailcomhostport=587username=mailusernamepassword=mailpasswordgt

ltrecipientaddress=xiemengjungmailcomgt

ltsmtpgt

ltfiltergt

ltoutputsgt

ltformatsgt

ltformatid=commonformat=DateTime[LEV]Msgngt

ltformatid=criticalformat=FileFullPathFuncMsgngt

ltformatid=criticalemailformat=CriticalerroronourservernTimeDateRelFileFuncMsgnSent

bySeeloggt

ltformatsgt

ltseeloggt

loggererr=seelogLoggerFromConfigAsBytes([]byte(appConfig))

iferr=nil

fmtPrintln(err)

return

UseLogger(logger)

funcinit()

DisableLog()

loadAppConfig()

DisableLogdisablesalllibrarylogoutput

funcDisableLog()

Logger=seelogDisabled

UseLoggerusesaspecifiedseelogLoggerInterfacetooutputlibrarylog

UsethisfuncifyouareusingSeelogloggingsysteminyourapp

funcUseLogger(newLoggerseelogLoggerInterface)

Logger=newLogger

Theaboveimplementsthethreemainfunctions

DisableLog

InitializesaglobalvariableLoggerwithseelogdisabledmainlyinordertopreventtheloggerfrombeingrepeatedlyinitialized

LoadAppConfig

InitializestheconfigurationsettingsofseelogaccordingtoaconfigurationfileInourexamplewearereadingtheconfigurationfromanin-memorystringbutofcourseyoucanreaditfromanXMLfilealsoInsidetheconfigurationwesetupthefollowingparameters

Seelog

TheminlevelparameterisoptionalIfconfiguredlogginglevelswhicharegreaterthanorequaltothespecifiedlevelwillberecordedTheoptionalmaxlevelparameterissimilarlyusedtoconfigurethemaximumloggingleveldesired

Outputs

ConfigurestheoutputdestinationInourparticularcasewechannelourloggingdataintotwooutputdestinationsThefirstisarollinglogfilewherewecontinuouslysavethemostrecentwindowofloggingdataTheseconddestinationisafilteredlogwhichrecordsonlycriticallevelerrorsWeadditionallyconfigureittoalertusviaemailwhenthesetypesoferrorsoccur

Formats

DefinesthevariousloggingformatsYoucanusecustomformattingorpredefinedformatting-afulllistofpredefinedformatscanbefoundonseelogswiki

UseLogger

Setthecurrentloggerasourlogprocessor

AbovewevedefinedandconfiguredacustomlogprocessingpackageThefollowingcodedemonstrateshowweduseit

packagemain

import(

nethttp

projectlogs

projectconfigs

projectroutes

funcmain()

addr_=configsMainConfigString(serveraddr)

logsLoggerInfo(Startserveratvaddr)

err=httpListenAndServe(addrroutesNewMux())

logsLoggerCritical(Servererrverr)

EmailnotificationsTheaboveexampleexplainshowtosetupemailnotificationswithseelogAsyoucanseeweusedthefollowingsmtpconfiguration

ltsmtpformatid=criticalemailsenderaddress=astaxiegmailcomsendername=ShortUrlAPIhostname=smtpgmailcom

hostport=587username=mailusernamepassword=mailpasswordgt

ltsmtpgt

WesettheformatofouralertmessagesthroughthecriticalemailconfigurationprovidingourmailserverparameterstobeabletoreceivethemWecanalsoconfigureournotifiertosendoutalertstoadditionalusersusingtherecipientconfigurationItsasimplematterofaddingonelineforeachadditionalrecipient

Totestwhetherornotthiscodeisworkingproperlyyoucanaddafakecriticalmessagetoyourapplicationlikeso

logsLoggerCritical(testCriticalmessage)

Dontforgettodeleteitonceyouredonetestingorwhenyourapplicationgoesliveyourinboxmaybefloodedwithemailnotifications

NowwheneverourapplicationlogsacriticalmessagewhileonlineyouandyourspecifiedrecipientswillreceiveanotificationemailYouandyourteamcanthenprocessandremedythesituationinatimelymanner

UsingapplicationlogsWhenitcomestologseachapplicationsuse-casemayvaryForexamplesomepeopleuselogsfordataanalysispurposesothersforperformanceoptimizationSomelogsareusedtoanalyzeuserbehaviorandhowpeopleinteractwithyourwebsiteOfcoursetherearelogswhicharesimplyusedtorecordapplicationeventsasauxiliarydataforfindingproblems

AsanexampleletssayweneedtotrackuserattemptsatloggingintooursystemThisinvolvesrecordingbothsuccessfulandunsuccessfulloginattemptsintoourlogWedtypicallyusetheInfologleveltorecordthesetypesofeventsratherthansomethingmoreseriouslikewarnIfyoureusingalinux-typesystemyoucanconvenientlyviewallunsuccessfulloginattemptsfromthelogusingthegrepcommandlikeso

catdatalogsrolllog|grepfailedlogin

2012-12-11111200WARNfailedloginattemptfrom11223344usernamepassword

ThiswaywecaneasilyfindtheappropriateinformationinourapplicationlogwhichcanhelpustoperformstatisticalanalysisifneededInadditionwealsoneedtoconsiderthesizeoflogsgeneratedbyhigh-trafficwebapplicationsTheselogscansometimesgrowunpredictablyToresolvethisissuewecansetseelogupwiththelogrotateconfigurationtoensurethatsinglelogfilesdonotconsumeexcessivediskspace

SummaryInthissectionwevelearnedthebasicsofseelogandhowtobuildacustomloggingsystemwithitWesawthatwecaneasilyconfigureseelogintoaspowerfulalogprocessingsystemasweneedusingittosupplyuswithreliablesourcesofdataforanalysisThroughloganalysiswecanoptimizeoursystemandeasilylocatethesourcesofproblemswhentheyariseInadditionseelogshipswithvariousdefaultloglevelsWecanusetheminlevelconfigurationinconjunctionwithalogleveltoeasilysetuptestsorsendautomatednotificationmessages

LinksDirectoryPrevioussectionDeploymentandmaintenanceNextsectionErrorsandcrashes

122ErrorsandcrashesOnceourwebapplicationsgoliveitslikelythattherewillbesomeunforeseenerrorsAfewexampleofcommonerrorsthatmayoccurinthecourseofyourapplicationsdailyoperationsarelistedbelow

DatabaseErrorserrorsrelatedtoaccessingthedatabaseserverorstoreddataThefollowingaresomedatabaseerrorswhichyoumayencounter

ConnectionErrorsindicatesthataconnectiontothenetworkdatabaseservercouldnotbeestablishedasuppliedusernameorpasswordisincorrectorthatthedatabasedoesnotexist

QueryErrorstheillegalorincorrectuseofanSQLquerycanraiseanerrorsuchasthisThesetypesoferrorscanbeavoidedthroughrigoroustestingDataErrorsdatabaseconstraintviolationsuchasattemptingtoinsertafieldwithaduplicateprimarykeyThesetypesoferrorscanalsobeavoidedthroughrigoroustestingbeforedeployingyourapplicationintoaproductionenvironmentApplicationRuntimeErrorsThesetypesoferrorsvarygreatlycoveringalmostallerrorcodeswhichmayappearduringruntimePossibleapplicationerrorsareasfollows

FilesystemandpermissionerrorswhentheapplicationattemptstoreadafilewhichdoesnotexistordoesnothavepermissiontoreadorwhenitattemptstowritetoafilewhichitisnotallowedtowritetoerrorsofthiscategorywilloccurAfilesystemerrorwillalsooccurifanapplicationreadsafilewithanunexpectedformatforinstanceaconfigurationfilethatshouldbeintheINIformatbutisinsteadstructuredasJSON

Third-partyapplicationerrorsTheseerrorsoccurinapplicationswhichinterfacewithotherthird-partyapplicationsorservicesForinstanceifanapplicationpublishestweetsaftermakingcallstoTwittersAPIitsobviousthatTwittersservicesmustbeupandrunninginorderforourapplicationtocompleteitstaskWemustalsoensurethatwesupplythesethird-partyinterfaceswiththeappropriateparametersinourcallsorelsetheywillalsoreturnerrors

HTTPerrorsTheseerrorsvarygreatlyandarebasedonuserrequestsThemostcommonisthe404NotFounderrorwhichariseswhenusersattempttoaccessnon-existentresourcesinyourapplicationAnothercommonHTTPerroristhe401Unauthorizederror(authenticationisrequiredtoaccesstherequestedresource)403Forbiddenerror(usersarealtogetherrefusedaccesstothisresource)and503ServiceUnavailableerrors(indicativeofaninternalprogramerror)

OperatingsystemerrorsThesesortsoferrorsoccurattheoperatingsystemlayerandcanhappenwhenoperatingsystemresourcesareover-allocatedleadingtocrashesandsysteminstabilityAnothercommonoccurrenceatthisleveliswhentheoperatingsystemdiskgetsfilledtocapacitymakingitimpossibletowritetoThisnaturallyproducesinmanyerrorsNetworkerrorsnetworkerrorstypicallycomeintwoflavorsoneiswhenusersissuerequeststotheapplicationandthenetworkdisconnectsthusdisruptingitsprocessingandresponsephaseTheseerrorsdonotcausetheapplicationtocrashbutcanaffectuseraccesstothewebsitetheotheriswhenapplicationsattemptstoreaddatafromdisconnectednetworkscausingreadfailuresJudicioustestingisparticularlyimportantwhenmakingnetworkcallstoavoidsuchproblemswhichcancauseyourapplicationtocrash

ErrorhandlinggoalsBeforeimplementingerrorhandlingwemustbeclearaboutwhatgoalswearetryingtoachieveIngeneralerrorhandlingsystemsshouldaccomplishthefollowing

UsererrornotificationswhensystemorusererrorsoccurcausingcurrentuserrequeststofailtocompleteaffectedusersshouldbenotifiedoftheproblemForexampleforerrorscausebyuserrequestsweshowaunifiederrorpage(404html)Whenasystemerroroccursweuseacustomerrorpagetoprovidefeedbackforusersastowhathappened-forinstancethatthesystemistemporarilyunavailable(errorhtml)Logerrorswhensystemerrorsoccur(ingeneralwhenfunctionsreturnnon-nilerrorvariables)aloggingsystemsuch

Errorsandcrashes

astheonedescribedearliershouldbeusedtorecordtheeventintoalogfilefileIfitisafatalerrorthesystemadministratorshouldalsobenotifiedviae-mailIngeneralhowevermost404errorsdonotwarrantthesendingofemailnotificationsrecordingtheeventintoalogforlaterscrutinyisoftenadequateRollbackthecurrentrequestoperationIfauserrequestcausesaservererrorthenweneedtobeabletorollbackthecurrentoperationLetslookatanexampleasystemsavesauser-submittedformtoitsdatabasethensubmitsthisdatatoathird-partyserverHoweverthethird-partyserverdisconnectsandweareunabletoestablishaconnectionwithitwhichresultsinanerrorInthiscasethepreviouslystoredformdatashouldbedeletedfromthedatabase(voidshouldbeinformed)andtheapplicationshouldinformtheuserofthesystemerrorEnsurethattheapplicationcanrecoverfromerrorsweknowthatitsdifficultforanyprogramtoguarantee100uptimesoweneedtomakeprovisionforscenarioswhereourprogramsfailForinstanceifourprogramcrasheswefirstneedtologtheerrornotifytherelevantpartiesinvolvedthenimmediatelygettheprogramupandrunningagainThiswayourapplicationcancontinuetoprovideserviceswhileasystemadministratorinvestigatesandfixesthecauseoftheproblem

HowtohandleerrorsInchapter11weaddressedtheprocessoferrorhandlinganddesignusingsomeexamplesLetsgointotheseexamplesinabitmoredetailandseesomeothererrorhandlingscenarios

Notifytheuseroferrors

Whenanerroroccurswecanpresenttheuseraccessingthepagewithtwokindsoferrorspages404htmlanderrorhtmlHereisanexampleofwhatthesourcecodeofanerrorpagemightlooklike

lthtmllang=engt

ltheadgt

ltmetahttp-equiv=Content-Typecontent=texthtmlcharset=utf-8gt

lttitlegtPageNotFound

lttitlegt

ltmetaname=viewportcontent=width=device-widthinitial-scale=10gt

ltheadgt

ltbodygt

ltdivclass=containergt

ltdivclass=rowgt

ltdivclass=span10gt

ltdivclass=hero-unitgt

lth1gt404lth1gt

ltpgtErrorInfoltpgt

ltdivgt

lt--span--gt

ltdivgt

ltbodygt

lthtmlgt

Anotherexample

Errorsandcrashes

lthtmllang=engt

ltheadgt

lttitlegtsystemerrorpage

lttitlegt

ltheadgt

ltbodygt

ltdivclass=rowgt

ltdivclass=span10gt

lth1gtsystemistemporarilyunavailablelth1gt

ltpgtErrorInfoltpgt

ltdivgt

lt--span--gt

ltdivgt

ltbodygt

lthtmlgt

404error-handlinglogicintheoccurrenceofasystemerror

ifrURLPath==

sayhelloName(wr)

return

NotFound404(wr)

return

funcNotFound404(whttpResponseWriterrhttpRequest)

logError(pagenotfound)errorlogging

t_=tParseFiles(tmpl404htmlnil)parsethetemplatefile

ErrorInfo=FilenotfoundGetthecurrentuserinformation

tExecute(wErrorInfo)executethetemplatemergeroperation

funcSystemError(whttpResponseWriterrhttpRequest)

logCritical(SystemError)systemerrortriggeredCriticalthenloggingwillnotonly

sendamessage

t_=tParseFiles(tmplerrorhtmlnil)parsethetemplatefile

ErrorInfo=systemistemporarilyunavailableGetthecurrentuserinformation

HowtohandleexceptionsWeknowthatmanyotherlanguageshavetrycatchkeywordsusedtocapturetheunusualcircumstancesbutinfactmanyerrorscanbeexpectedtooccurwithouttheneedforexceptionhandlingandcanbeinsteadtreatedasanerrorsItsforthisreasonthatGofunctionsreturnerrorsbydesignForexampleifafileisnotfoundorifosOpenreturnsanerrorthesefunctionswillnotpanicasanotherexampleifanetworkconnectiongetsdisconnectedduringadatawriteoperationthenetConnfamilyofWritefunctionswillreturnerrorsinsteadofpanickingTheseerrorstatesaretobeexpectedinmostapplicationsandGoparticularlymakesitexplicitwhenoperationsmightfailbyreturningerrorvariablesLookingattheexampleabovewecanclearlyseetheerrorsthatcanbeexpectedtooccur

Errorsandcrashes

TherearehowevercaseswherepanicshouldbeusedForinstanceinoperationswherefailureisalmostimpossibleorincertainsituationswherethereisnowaytoreturnanerrorandtheoperationcannotcontinuepanicshouldbeusedTakeforexampleaprogramthattriestoobtainthevalueofanarrayatx[j]buttheindexjisoutofboundsThispartofthecodewillcausetheprogramtopanicaswillothercriticalunexpectederrorsofthisnatureBydefaultpanickingwillkillofftheoffendingprocess(goroutine)allowingthecodewhichdispatchedthegoroutineanopportunitytorecoverfromtheerrorThiswaythefunctioninwhichtheerroroccurredaswellasallsubsequentcodeafteritwillnotcontinuetoexecuteGospanicwasdeliberatelydesignedwiththisbehaviorinmindwhichisdifferentthantypicalerrorhandlingpanicisreallyjustexceptionhandlingIntheexamplebelowweexpectthatUser[UID]willreturnausernamefromtheUserarraybuttheUIDthatweuseisoutofboundsandthrowsanexceptionIfwedonothavearecoverymechanismtodealwiththisimmediatelytheprocesswillbekilledandthepanicwillpropagateupthestackuntilourprogramfinallycrashesInorderforourapplicationtoberobustandresilienttothesekindsofruntimeerrorsweneedtoimplementrecoverymechanismsincertainplaces

funcGetUser(uidint)(usernamestring)

deferfunc()

ifx=recover()x=nil

username=

username=User[uid]

return

TheabovedescribesthedifferencesbetweenerrorsandexceptionsSowhenitcomesdowntodevelopingourGoapplicationswhendoweuseoneortheotherTherulesaresimpleifyoudefineafunctionthatyouanticipatemightfailthenreturnanerrorvariableWhencallinganotherpackagesfunctionifitisimplementedwellthereshouldbenoneedtoworrythatitwillpanicunlessatrueexceptionhasoccurred(whetherrecoverylogichasbeenimplementedornot)PanicandrecovershouldonlybeusedinternallyinsidepackagestodealwithspecialcaseswherethestateoftheprogramcannotbeguaranteedorwhenaprogrammerserrorhasoccurredExternallyfacingAPIsshouldexplicitlyreturnerrorvalues

SummaryThisissectionsummarizeshowwebapplicationsshouldhandlevariouserrorssuchasnetworkdatabaseandoperatingsystemerrorsamongothersWeveoutlineseveraltechniquestoeffectivelydealwithruntimeerrorssuchasdisplayinguser-friendlyerrornotificationsrollingbackactionsloggingandalertingsystemadministratorsFinallyweexplainedhowtocorrectlyhandleerrorsandexceptionsTheconceptofanerrorisoftenconfusedwiththatofanexceptionhoweverinGothereisacleardistinctionbetweenthetwoForthisreasonwevediscussedtheprinciplesofprocessingbotherrorsandexceptionsinwebapplications

LinksDirectoryPrevioussectionLogsNextsectionDeployment

Errorsandcrashes

123DeploymentWhenourwebapplicationisfinallyproductionreadywhatarethestepsnecessarytogetitdeployedInGoanexecutablefileencapsulatingourapplicationiscreatedafterwecompileourprogramsProgramswritteninCcanrunperfectlyasbackgrounddaemonprocesseshoweverGodoesnotyethavenativesupportfordaemonsThegoodnewsisthatwecanusethirdpartytoolstohelpusmanagethedeploymentofourGoapplicationsexamplesofwhichareSupervisordupstartanddaemontoolsamongothersThissectionwillintroduceyoutosomebasicsoftheSupervisordprocesscontrolsystem

DaemonsCurrentlyGoprogramscannotberunasdaemonprocesses(foradditionalinformationseetheopenissueongithubhere)ItsdifficulttoforkexistingthreadsinGobecausethereisnowayofensuringaconsistentstateinallthreadsthathavebeenused

Wecanhoweverseemanyattemptsatimplementingdaemonsonlinesuchasinthetwofollowingways

MarGooneimplementationoftheconceptofusingCommandtodeployapplicationsIfyoureallywanttodaemonizeyourapplicationsitisrecommendedtousecodesimilartothefollowing

d=flagBool(dfalseWhetherornottolaunchinthebackground(likea

daemon))

cmd=execCommand(osArgs[0]

-close-fds

-addraddr

-callcall

serrerr=cmdStderrPipe()

iferr=nil

logFatalln(err)

err=cmdStart()

iferr=nil

logFatalln(err)

serr=ioutilReadAll(serr)

s=bytesTrimSpace(s)

ifbytesHasPrefix(s[]byte(addr))

fmtPrintln(string(s))

cmdProcessRelease()

logPrintf(unexpectedresponsefromMarGo`s`error`v`nserr)

cmdProcessKill()

Anothersolutionistousesyscallbutthissolutionisnotperfect

Deployment

packagemain

import(

syscall

funcdaemon(nochdirnocloseint)int

varretret2uintptr

varerruintptr

darwin=syscallOS==darwin

alreadyadaemon

ifsyscallGetppid()==1

return0

forkofftheparentprocess

retret2err=syscallRawSyscall(syscallSYS_FORK000)

iferr=0

return-1

failure

ifret2lt0

osExit(-1)

handleexceptionfordarwin

ifdarwinampampret2==1

ifwegotagoodPIDthenwecallexittheparentprocess

ifretgt0

osExit(0)

Changethefilemodemask

_=syscallUmask(0)

createanewSIDforthechildprocess

s_rets_errno=syscallSetsid()

ifs_errno=0

logPrintf(ErrorsyscallSetsiderrnods_errno)

ifs_retlt0

return-1

ifnochdir==0

osChdir()

ifnoclose==0

fe=osOpenFile(devnullosO_RDWR0)

ife==nil

fd=fFd()

syscallDup2(fdosStdinFd())

syscallDup2(fdosStdoutFd())

syscallDup2(fdosStderrFd())

return0

Deployment

WhilethetwosolutionsaboveimplementdaemonizationinGoIstillcannotrecommendthatyouuseeithermethodssincethereisnoofficialsupportfordaemonsinGoNotwithstandingthisfactthefirstoptionisthemorefeasibleoneandiscurrentlybeingusedbysomewell-knownopensourceprojectslikeskynetforimplementingdaemons

SupervisordAbovewevelookedattwoschemesthatarecommonlyusedtoimplementdaemonsinGohoweverbothmethodslackofficialsupportSoitsrecommendedthatyouuseathird-partytooltomanageapplicationdeploymentHerewetakealookattheSupervisordprojectimplementedinPythonwhichprovidesextensivetoolsforprocessmanagementSupervisordwillhelpyoutodaemonizeyourGoapplicationsalsoallowingyoutodothingslikestartshutdownandrestartyourapplicationswithsomesimplecommandsamongmanyotheractionsInadditionSupervisordmanagedprocessescanautomaticallyrestartprocesseswhichhavecrashedensuringthatprogramscanrecoverfromanyinterruptions

AsanasideIrecentlyfellintoacommonpitfallwhiletryingtodeployanapplicationusingSupervisordAllapplicationsdeployedusingSupervisordarebornoutoftheSupervisordparentprocessWhenyouchangeanoperatingsystemfiledescriptordontforgettocompletelyrestartSupervisord-simplyrestartingtheapplicationitismanagingwillnotsufficeWhenIfirstdeployedanapplicationwithSupervisordImodifiedthedefaultfiledescriptorfieldchangingthedefaultnumberfrom1024to100000andthenrestartingmyapplicationInrealitySupervisordcontinuedusingonly1024filedescriptorstomanageallofmyapplicationsprocessesUpondeployingmyapplicationtheloggerbeganreportingalackoffiledescriptorsItwasalongprocessfindingandfixingthismistakesobeware

InstallingSupervisord

Supervisordcaneasilybeinstalledusingsudoeasy_installsupervisorOfcoursethereisalsotheoptionofdirectlydownloadingitfromitsofficialwebsiteuncompressingitgoingintothefolderthenrunningsetuppyinstalltoinstallitmanually

Ifyouregoingtheeasy_installroutethenyouneedtofirstinstallsetuptools

GotohttppypipythonorgpypisetuptoolsfilesanddownloadtheappropriatefiledependingonyoursystemspythonversionEnterthedirectoryandexecuteshsetuptoolsxxxxeggWhenthenscriptisdoneyoullbeabletousetheeasy_installcommandtoinstallSupervisord

ConfiguringSupervisord

SupervisordsdefaultconfigurationfilepathisetcsupervisordconfandcanbemodifiedusingatexteditorThefollowingiswhatatypicalconfigurationfilemaylooklike

Deployment

etcsupervisordconf

[unix_http_server]

file=varrunsupervisordsock

chmod=0777

chown=rootroot

[inet_http_server]

Webmanagementinterfacesettings

port=9001

username=admin

password=yourpassword

[supervisorctl]

Mustunix_http_servermatchthesettingsinside

serverurl=unixvarrunsupervisordsock

[supervisord]

logfile=varlogsupervisordsupervisordlog(mainlogfiledefault$CWDsupervisordlog)

logfile_maxbytes=50MB(maxmainlogfilebytesb4rotationdefault50MB)

logfile_backups=10(numofmainlogfilerotationbackupsdefault10)

loglevel=info(logleveldefaultinfoothersdebugwarntrace)

pidfile=varrunsupervisordpid(supervisordpidfiledefaultsupervisordpid)

nodaemon=true(startinforegroundiftruedefaultfalse)

minfds=1024(minavailstartupfiledescriptorsdefault1024)

minprocs=200(minavailprocessdescriptorsdefault200)

user=root(defaultiscurrentuserrequiredifroot)

childlogdir=varlogsupervisord(AUTOchildlogdirdefault$TEMP)

[rpcinterfacesupervisor]

supervisorrpcinterface_factory=supervisorrpcinterfacemake_main_rpcinterface

Managetheconfigurationofasingleprocessyoucanaddmultipleprogram

[programblogdemon]

command=datablogblogdemon

autostart=true

startsecs=5

user=root

redirect_stderr=true

stdout_logfile=varlogsupervisordblogdemonlog

SupervisordmanagementAfterinstallationiscompletetwoSupervisordcommandsbecomeavailabletoyouonthecommandlinesupervisorandsupervisorctlThecommandsareasfollows

supervisordinitialstartuplaunchandprocessconfigurationmanagementsupervisorctlstopprogramxxxstoptheprogramxxxprocesswhereprogramxxxisavalueconfiguredinyoursupervisordconffileForinstanceifyouhavesomethinglike[programblogdemon]configuredyouwouldusethesupervisorctlstopblogdemoncommandtokilltheprocesssupervisorctlstartprogramxxxstarttheprogramxxxprocesssupervisorctlrestartprogramxxxrestarttheprogramxxxprocesssupervisorctlstopallstopallprocessesnotestartrestartstopwillnotloadthelatestconfigurationfilessupervisorctlreloadloadthelatestconfigurationfilelaunchthemandmanageallprocesseswiththenewconfiguration

SummaryInthissectionwedescribedhowtoimplementdaemonsinGoWelearnedthatGodoesnotnativelysupportdaemonsandthatweneedtousethird-partytoolstohelpusmanagethemOnesuchtoolistheSupervisordprocesscontrolsystemwhichwecanusetoeasilydeployandmanageourGoprograms

Deployment

DirectoryPrevioussectionErrorsandcrashesNextsectionBackupandrecovery

Deployment

124BackupandrecoveryInthissectionwelldiscussanotheraspectofapplicationmanagementdatabackupandrecoveryonproductionserversWeoftenencountersituationswhereproductionserversdontbehaveasweexpectthemtoServernetworkoutagesharddrivemalfunctionsoperatingsystemcrashesandothersimilareventscancausedatabasestobecomeunavailableTheneedtorecoverfromthesetypesofeventshasledtotheemergenceofmanycoldstandbyhotstandbytoolsthatcanhelptofacilitatedisasterrecoveryremotelyInthissectionwellexplainhowtobackupdeployedapplicationsinadditiontobackingupandrestoringanyMySQLandRedisdatabasesyoumightbeusing

ApplicationBackupInmostclusterenvironmentswebapplicationsdonotneedtobebackedupsincetheyareactuallycopiesofcodefromourlocaldevelopmentenvironmentorfromaversioncontrolsystemInmanycaseshoweverweneedtobackupdatawhichhasbeensuppliedbytheusersofoursiteForinstancewhensitesrequireuserstouploadfilesweneedtobeabletobackupanyfilesthathavebeenuploadedbyuserstoourwebsiteThecurrentapproachforprovidingthiskindofredundancyistoutilizeso-calledcloudstoragewhereuserfilesandotherrelatedresourcesarepersistedintoahighlyavailablenetworkofserversIfoursystemcrashesaslongasuserdatahasbeenpersistedontothecloudwecanatleastbesurethatnodatawillbelost

ButwhataboutthecaseswherewedidnotbackupourdatatoacloudserviceorwherecloudstoragewasnotanoptionHowdowebackupdatafromourwebapplicationsthenHerewedescribeatoolcalledrsyncwhichcanbecommonlyfoundonunix-likesystemsRsyncisatoolwhichcanbeusedtosynchronizefilesresidingondifferentsystemsandaperfectuse-caseforthisfunctionalityistokeepourwebsitebackedup

NoteCwrsyncisanimplementationofrsyncfortheWindowsenvironment

RsyncinstallationYoucanfindthelatestversionofrsyncfromitsofficialwebsiteOfcoursebecausersyncisveryusefulsoftwaremanyLinuxdistributionswillalreadyhaveitinstalledbydefault

PackageInstallation

sudoapt-getinstallrsyncNotedebianubuntuandotheronlineinstallationmethods

yuminstallrsyncNoteFedoraRedhatCentOSandotheronlineinstallationmethods

rpm-ivhrsyncNoteFedoraRedhatCentOSandotherrpmpackageinstallationmethods

FortheotherLinuxdistributionspleaseusetheappropriatepackagemanagementmethodstoinstallitAlternativelyyoucanbuildityourselffromthesource

tarxvfrsync-xxxtargz

cdrsync-xxx

configure-prefix=usrmakemakeinstall

NoteIfwanttocompileandinstallthersyncfromitssourceyouhavetoinstallgcccompilertoolssuchasjob

NoteBeforeusingsourcepackagescompiledandinstalledyouhavetoinstallgcccompilertoolssuchasjob

RsyncConfiguration

Rsynccanbeconfiguredfromthreemainconfigurationfilesrsyncdconfwhichisthemainconfigurationfilersyncdsecretswhichholdspasswordsandrsyncdmotdwhichcontainsserverinformation

Backupandrecovery

Youcanrefertotheofficialdocumentationonrsyncswebsiteformoredetailedexplanationsbutherewewillsimplyintroducethebasicsofsettinguprsync

Startinganrsyncdaemonserver-side

usrbinrsync--daemon--config=etcrsyncdconf

the--daemonparameterisforrunningrsyncinservermodeMakethisthedefaultboot-timesettingbyjoiningittotherclocalfile

echorsync--daemongtgtetcrcdrclocal

SetupanrsyncusernameandpasswordmakingsurethatitsownedonlybyrootsothatlocalunauthorizedusersorexploitsdonothaveaccesstoitIfthesepermissionsarenotsetcorrectlyrsyncmaynotboot

echoYourUsernameYourPasswordgtetcrsyncdsecrets

chmod600etcrsyncdsecrets

Clientsynchronization

Clientscansynchronizeserverfileswiththefollowingcommand

rsync-avzP--delete--password-file=rsyncdsecretsusername1921681455wwwvarrsyncbackup

Letsbreakthisdownintoafewkeypoints

1 -avzParesomecommonoptionsUsersync--helptoreviewwhatthesedo2 --deletedeletesextraneousfilesonthereceivingsideForexampleiffilesaredeletedonthesendingsidethenext

timethetwomachinesaresynchronizedthereceivingsideswillautomaticallydeletethecorrespondingfiles3 --password-filespecifiesapasswordfileforaccessinganrsyncdaemonOntheclientsidethisistypicallythe

clientetcrsyncdsecretsfileandontheserversideitsetcrsyncdsecretsWhenusingsomethinglikeCrontoautomatersyncyouwontneedtomanuallyenterapassword

4 usernamespecifiestheusernametobeusedinconjunctionwiththeserver-sideetcrsyncdsecretspassword5 1921681455istheIPaddressoftheserver6 www(notethedoublecolons)specifiescontactinganrsyncdaemondirectlyviaTCPforsynchronizingthewww

moduleaccordingtotheserver-sideconfigurationslocatedinetcrsyncdconfWhenonlyasinglecolonisusedthersyncdaemonisnotcontacteddirectlyinsteadaremote-shellprogramsuchassshisusedasthetransport

InordertoperiodicallysynchronizefilesyoucansetupacrontabfilethatwillrunrsynccommandsasoftenasneededOfcourseuserscanvarythefrequencyofsynchronizationaccordingtohowcriticalitistokeepcertaindirectoriesorfilesuptodate

MySQLbackupMySQLdatabasesarestillthemainstreamgo-tosolutionformostwebapplicationsThetwomostcommonmethodsofbackingupMySQLdatabasesarehotbackupsandcoldbackupsHotbackupsareusuallyusedwithsystemssetupinamasterslaveconfigurationtobackuplivedata(themasterslavesynchronizationmodeistypicallyusedforseparatingdatabasereadwriteoperationsbutcanalsobeusedforbackinguplivedata)ThereisalotofinformationavailableonlinedetailingthevariouswaysonecanimplementthistypeofschemeForcoldbackupsincomingdataisnotbackedupinreal-timeasisthecasewithhotbackupsInsteaddatabackupsareperformedperiodicallyThiswayifthesystemfailstheintegrityofdatabeforeacertainperiodoftimecanstillbeguaranteedForinstanceincaseswhereasystemmalfunctioncausesdatatobelostandthemasterslavemodelisunabletoretrieveitcoldbackupscanbeusedforapartialrestoration

Ashellscriptisgenerallyusedtoimplementregularcoldbackupsofdatabasesexecutingsynchronizationtasksusingrsyncinanon-localmode

Backupandrecovery

ThefollowingisanexampleofabackupscriptthatperformsscheduledbackupsforaMySQLdatabaseWeusethemysqldumpprogramwhichallowsustoexportthedatabasetoafile

binbash

Configurationinformationmodifyitasneeded

mysql_user=USERMySQLbackupuser

mysql_password=PASSWORDMySQLbackupuserspassword

mysql_host=localhost

mysql_port=3306

mysql_charset=utf8MySQLencoding

backup_db_arr=(db1db2)Nameofthedatabasetobebackedupseparatingmultipledatabaseswihspaces(DB1

DB2db3)

backup_location=varwwwmysqlBackupdatastoragelocationpleasedonotendwithaandleaveitatitsdefau

ltfortheprogramtoautomaticallycreateafolder

expire_backup_delete=ONWhethertodeleteoutdatedbackupsornot

expire_days=3Settheexpirationtimeofbackupsindays(defaultstothreedays)thisisonlyvalidwhenthe`ex

pire_backup_delete`optionisON

Wedonotneedtomodifythefollowinginitialsettingsbelow

backup_time=`date+YmdHM`Definethebackuptimeformat

backup_Ymd=`date+Y-m-d`Definethebackupdirectorydatetime

backup_3ago=`date-d3daysago+Y-m-d`3daysbeforethedate

backup_dir=$backup_location$backup_YmdFullpathtothebackupfolder

welcome_msg=WelcometouseMySQLbackuptoolsGreeting

DeterminewhethertoMySQLisrunningifnotthenabortthebackup

mysql_ps=`ps-ef|grepmysql|wc-l`

mysql_listen=`netstat-an|grepLISTEN|grep$mysql_port|wc-l`

if[[$mysql_ps==0]-o[$mysql_listen==0]]then

echoERRORMySQLisnotrunningbackupaborted

echo$welcome_msg

Connecttothemysqldatabaseifaconnectioncannotbemadeabortthebackup

mysql-h$mysql_host-P$mysql_port-u$mysql_user-p$mysql_passwordltltend

usemysql

selecthostuserfromuserwhereuser=rootandhost=localhost

flag=`echo$`

if[$flag=0]then

echoERRORCantconnectmysqlserverbackupaborted

echoMySQLconnectokPleasewait

DeterminewhetherabackupdatabaseisdefinedornotIfsobeginthebackupifnotthenabort

if[$backup_db_arr=]then

dbnames=$(cut-d-f1-5$backup_database)

echoarris($backup_db_arr[])

fordbnamein$backup_db_arr[]

echodatabase$dbnamebackupstart

`mkdir-p$backup_dir`

`mysqldump-h$mysql_host-P$mysql_port-u$mysql_user-p$mysql_password$dbname-default-character-set=

$mysql_charset|gzipgt$backup_dir$dbname-$backup_timesqlgz`

flag=`echo$`

if[$flag==0]then

echodatabase$dbnamesuccessfullybackedupto$backup_dir$dbname-$backup_timesqlgz

echodatabase$dbnamebackuphasfailed

echoERRORNodatabasetobackupbackupaborted

Ifdeletingexpiredbackupsisenableddeleteallexpiredbackups

Backupandrecovery

if[$expire_backup_delete==ON-a$backup_location=]then

`find$backup_location-typed-o-typef-ctime+$expire_days-execrm-rf`

`find$backup_location-typed-mtime+$expire_days|xargsrm-rf`

echoExpiredbackupdatadeletecomplete

echoAlldatabaseshavebeensuccessfullybackedupThankyou

Modifythepropertiesoftheshellscriptlikeso

chmod600rootmysql_backupsh

chmod+xrootmysql_backupsh

Thenaddthecrontabcommand

0000rootmysql_backupsh

Thissetsupregularbackupsofyourdatabasestothevarwwwmysqldirectoryeverydayat0000whichcanthenbesynchronizedusingrsync

MySQLRecoveryWevejustdescribedsomecommonlyusedbackuptechniquesforMySQLnamelyhotbackupsandcoldbackupsTorecapthemaingoalofahotbackupistobeabletorecoverdatainreal-timeafteranapplicationhasfailedinsomewaysuchasinthecaseofaserverhard-diskmalfunctionWelearnedthatthistypeofschemecanbeimplementedbymodifyingdatabaseconfigurationfilessothatdatabasesarereplicatedontoaslaveminimizinginterruptiontoservices

ButsometimesweneedtoperformacoldbackupoftheSQLdatarecoveryaswithdatabasebackupyoucanimportthroughthecommandHotbackupsarehoweversometimesinadequateTherearecertainsituationswherecoldbackupsarerequiredtoperformdatarecoveryevenifitsonlyapartialoneWhenyouhaveacoldbackupofyourdatabaseyoucanusethefollowingMySQLcommandtoimportit

mysql-uusername-pdatabseltbackupsql

AsyoucanseeimportingandexportingdatabaseisafairlysimplematterIfyouneedtomanageadministrativeprivilegesordealwithdifferentcharactersetsthisprocessmaybecomealittlemorecomplicatedthoughthereareanumberofcommandswhichwillhelpyoutodothis

RedisbackupRedisisoneofthemostpopularNoSQLdatabasesandbothhotandcoldbackuptechniquescanalsobeusedinsystemswhichuseitLikeMySQLRedisalsosupportsmasterslavemodewhichisidealforimplementinghotbackups(refertoRedisofficialdocumentationtolearnhowtoconfigurethistheprocessisverystraightforward)AsforcoldbackupsRedisroutinelysavescacheddatainmemorytothedatabasefileon-diskWecansimplyusethersyncbackupmethoddescribedabovetosynchronizeitwithanon-localmachine

RedisrecoverySimilarlyRedisrecoverycanbedividedintohotandcoldbackuprecoveryThemethodsandobjectivesofrecoveringdatafromahotbackupofaRedisdatabasearethesameasthosementionedaboveforMySQLaslongastheRedisapplicationisusingtheappropriatedatabaseconnection

Backupandrecovery

ARediscoldbackuprecoverysimplyinvolvescopyingbacked-updatabasefilesintotheworkingdirectorythenstartingRedisonitThedatabasefilesareautomaticallyloadedintomemoryatboottimethespeedwithwhichRedisbootswilldependonthesizeofthedatabasefiles

SummaryInthissectionwelookedatsometechniquesforbackingupdataaswellasrecoveringfromdisasterswhichmayoccurafterdeployingourapplicationsWealsointroducedrsyncatoolwhichcanbeusedtosynchronizefilesondifferentsystemsUsingrsyncwecaneasilyperformbackupandrestorationproceduresforbothMySQLandRedisdatabasesamongothersWehopethatbybeingintroducedtosomeoftheseconceptsyouwillbeabletodevelopdisasterrecoveryprocedurestobetterprotectthedatainyourwebapplications

LinksDirectoryPrevioussectionDeploymentNextsectionSummary

Backupandrecovery

125SummaryInthischapterwediscussedhowtodeployandmaintainourGowebapplicationsWealsolookedatsomecloselyrelatedtopicswhichcanhelpustokeepthemrunningsmoothlywithminimalmaintenance

Specificallywelookedat

CreatingarobustloggingsystemcapableofrecordingerrorsandnotifyingsystemadministratorsHandlingruntimeerrorsthatmayoccurincludingloggingthemandhowtorelaythisinformationinauser-friendlymannerthatthereisaproblemHandling404errorsandnotifyingusersthattherequestedpagecannotbefoundDeployingapplicationstoaproductionenvironment(includinghowtodeployupdates)HowtodeployhighlyavailableapplicationsBackingupandrestoringfilesanddatabases

Afterreadingthecontentsofthischapterthosethinkingaboutdevelopingawebapplicationfromscratchshouldalreadyhavethefullpictureonhowtodosothischapterprovidedanintroductiononhowtomanagedeploymentenvironmentswhilepreviouschaptershavefocusedonthedevelopmentofcode

LinksDirectoryPrevioussectionBackupandrecoveryNextchapterBuildingawebframework

Summary

13BuildingawebframeworkThePrecedingtwelvechaptersdescribehowtodevelopwebapplicationsinGointroducingalotofbasicknowledgedevelopmenttoolsandtechniquesInthischapterwewillbeusingthisknowledgetoimplementasimplewebframeworkThefirstsectionofthischapterwilltakeyouthroughtheplanninganddesignstageofbuildingawebframeworkWelllookatleveragingtheMVCpatternaswellasdesigningprogramexecutionflowamongotherthingsThesecondsectionwilldescribethefirstfeatureofourframeworkRoutingnamelyhowtomapURLstoprocessinglogicTheninthethirdsectionwedescribetheprocessinglogicitselfwhichinvolvesdesigninggenericcontrollersandhowtohandlerequestsandreturnresponsesafterinheritingfromanobjecthandlerNextwedescribesomeoftheauxiliaryfunctionalitycommontomostwebframeworkssuchaslogprocessinginformationconfigurationetcFinallywellimplementasimplebloggingsystemontopofourframeworkwhichwilldemonstratetheapplicationlogicnecessaryforpublishingmodifyingdeletinganddisplayinglistsofblogposts

Byseeingfirst-handhowtoimplementsuchacompleteprojectfromscratchyouwillhopefullyhaveabetterunderstandingoftheinnerworkingsofGowebapplicationsYoullbecomfortablebuildingyourownprojectdirectorystructuresimplementingURLroutersandutilizingMVCamongotheraspectsofwebdevelopmentAmongtheframeworksprevalenttodayMVCisnolongeramythItsnotuncommontohearprogrammersarguingaboutwhichframeworksaregoodandwhicharebadwhichisoftentooshallowofanapproachFrameworksareonlytoolsandsometoolsaremoresuitableforcertainapplicationsthanothersTherearenouniversallygoodorbadtoolsThusbyteachingyourselfhowtowriteaframeworkfromscratchyouwillbeabletotailor-maketheperfecttooltobestrealizeyourideas

LinksDirectoryPreviouschapterChapter12summaryNextsectionProjectprogram

Buildawebframework

131ProjectplanningAnythingyouintendtodowellmustfirstbeplannedwellInourcaseourintentionistodevelopabloggingsystemsothefirststepweshouldtakeistodesigntheflowoftheapplicationinitsentiretyWhenwehaveaclearunderstandingoftheourapplicationsprocessofexecutionthesubsequentdesignandcodingstepsbecomemucheasier

GOPATHandprojectsettingsLetsproceedbyassumingthatourGOPATHpointstoafolderwithanordinarydirectoryname(ifnotwecaneasilysetupasuitabledirectoryandsetitspathastheGOPATH)AswevedescribeearlieraGOPATHcancontainmorethanonedirectoryinWindowswecansetthisasanenvironmentvariableinlinuxOSXsystemsGOPATHcanbesetusingexportieexportgopath=pathtoyourdirectoryaslongasthedirectorywhichGOPATHpointstocontainsthethreesub-directoriespkgbinandsrcBelowweveplacedthesourcecodeofournewprojectinthesrcdirectorywiththetentativenamebeelogHerearesomescreenshotsoftheWindowsenvironmentvariablesaswellasofthedirectorystructure

Figure131SettingtheGOPATHenvironmentvariable

Figure132Theworkingdirectoryunder$gopathsrc

ApplicationflowchartOurbloggingsystemwillbebasedonthemodel-view-controllerdesignpatternMVCistheseparationoftheapplicationlogicfromthepresentationlayerInpracticewhenwekeepthepresentationlayerseparatedwecandrasticallyreducetheamountofcodeneededonourwebpages

ModelsrepresentdataaswellastherulesandlogicgoverningitInGeneralamodelclasswillcontainfunctionsforremovinginsertingandupdatingdatabaseinformationViewsarearepresentationofthestateofamodelAviewisusuallyapagebutinGoaviewcanalsobeafragmentofapagesuchasaheaderorfooterItcanalsobeanRSSfeedoranyothertypeofpageGostemplatepackageprovidesverygoodsupportforviewlayerfunctionalityControllersarethegluelogicbetweenthemodelandviewlayersandencompassesalltheintermediarylogicnecessaryforhandlingHTTPrequestsandgeneratingWebpages

Thefollowingfigureisanoverviewoftheprojectframeworkanddemonstrateshowdatawillflowthroughthesystem

Figure133frameworkdataflow

1 Maingoistheapplicationsentrypointandinitializessomebasicresourcesrequiredtoruntheblogsuchasconfigurationinformationlisteningportsetc

2 RoutingchecksallincomingHTTPrequestsandaccordingtothemethodURLandparametersmatchesitwiththecorrespondingcontrolleraction

3 Iftherequestedresourcehasalreadybeencachedtheapplicationwillbypasstheusualexecutionprocessandreturnaresponsedirectlytotheusersbrowser

4 SecuritydetectionTheapplicationwillfilterincomingHTTPrequestsandanyotherusersubmitteddatabeforehandingitofftothecontroller

5 ControllerloadsmodelscorelibrariesandanyotherresourcesrequiredtoprocessspecificrequestsThecontrollerisprimarilyresponsibleforhandlingbusinesslogic

Projectprogram

6 OutputtherenderedviewtobesenttotheclientswebbrowserIfcachinghasbeenenabledthefirstviewiscachedforfuturerequeststothesameresource

DirectorystructureAccordingtotheframeworkflowwevedesignedaboveourblogprojectsdirectorystructureshouldlooksomethinglikethefollowing

|mdashmdashmaingoimportdocuments

|mdashmdashconfconfigurationfilesandprocessingmodule

|mdashmdashcontrollerscontrollerentry

|mdashmdashmodelsdatabaseprocessingmodule

|mdashmdashutilsusefulfunctionlibrary

|mdashmdashstaticstaticfiledirectory

|mdashmdashviewsviewgallery

FrameworkdesignInordertoquicklybuildourblogweneedtodevelopaminimalframeworkbasedontheapplicationwevedesignedaboveTheframeworkshouldincluderoutingcapabilitiessupportforRESTfulcontrollersautomatedtemplaterenderingaloggingsystemconfigurationmanagementandmore

SummaryThissectiondescribestheinitialdesignofourbloggingsystemfromsettingupourGOPATHtobrieflyintroducingtheMVCpatternWealsolookedattheflowofdataandtheexecutionsequenceofourbloggingsystemFinallywedesignedthestructureofourprojectdirectoryAtthispointwevebasicallycompletedthegroundworkrequiredforassemblingourframeworkInthenextfewsectionswewillimplementeachofthecomponentswevediscussedonebyone

LinksDirectoryPrevioussectionBuildingawebframeworkNextsectionCustomizingrouters

Projectprogram

132Customizingrouters

HTTProutingTheHTTProutingcomponentisresponsibleformappingHTTPrequeststoacorrespondingfunctionorstructmethodTheroutertakestwokeypiecesofinformationfromincomingrequests

-Theuserrequestedpath(forexampleuser123article123)andanyquerystringsorparametersthatcomewithit(forexampleid=11)-TheHTTPrequestmethod(GETPOSTPUTandDELETEPATCHetc)

Therouterthenforwardstherequesttothehandlerfunction(controllerlayer)thathasbeenregisteredwiththatparticularHTTPmethodandpath

DefaultroutingimplementationInsection34weintroducedGoshttppackageindetailwhichincludedhowtodesignandimplementroutingHerewetakeanotherlookatanexamplethatillustratestheroutingprocess

funcfooHandler(whttpResponseWriterrhttpRequest)

fmtFprintf(wHelloqhtmlEscapeString(rURLPath))

httpHandle(foofooHandler)

httpHandleFunc(barfunc(whttpResponseWriterrhttpRequest)

logFatal(httpListenAndServe(8080nil))

TheexampleabovecallshttpsdefaultmuxcalledDefaultServeMuximplicitlyspecifiedbythenilparameterinthecalltohttpListenAndServeThehttpHandlefunctiontakestwoparametersthefirstparameteristheresourceyouwantuserstoaccessspecifiedbyitsURLpath(whichisstoredinrURLPath)andthesecondargumentbindsahandlerfunctionwiththispathTheRouterhastwomainjobs

ToaddandstoreroutinginformationToforwardrequeststoahandlerfunctionforprocessing

BydefaultGoroutesarehandledwithhttpHandleandhttpHandleFunctypesregisteredbydefaultthroughtheunderlyingDefaultServeMuxHandle(patternstringhandlerHandler)functionThisfunctionmapsresourcepathstohandlersandstorestheminamap[string]muxEntrymapThisisthefirstjobthatwementionedabove

WhentheapplicationisrunningtheGoserverlistenstoaportWhenitreceivesatcpconnectionitusesaHandlertoprocessitAsaforementionedsincetheHandlerintheexampleaboveisnilthedefaultrouterhttpDefaultServeMuxisusedUsingthemapofpreviouslystoredroutesDefaultServeMuxServeHTTPwilldispatchtherequesttothefirsthandlerwithamatchingpathThisistherouterssecondjob

forkv=rangemuxm

ifpathMatch(kpath)

continue

ifh==nil||len(k)gtn

n=len(k)

Customizedrouters

RoutingwithBeegoAtpresentmostGowebapplicationsbasetheirroutingonhttpsdefaultrouterhoweverthishasseverallimitations

DoesnotsupportdynamicrouteswithparameterssuchastheuserUIDDoesnothavegoodsupportforRESTTheaccessmethodscannotberestrictedforinstanceintheaboveexamplewhenusersaccessfootheycanusetheGETPOSTDELETEandHEADHTTPmethodsamongothersInlargeappsroutingrulescanbecomerepetitiveandcumbersomePersonallyIvedevelopedsimplewebAPIscomposedofnearlythirtyroutingruleswheninfacttheserulescouldhavebeenfurthersimplifiedusingmethodstructs

TheBeegoframeworksrouterisdesignedtoovercometheselimitationstakingtheRESTparadigmintoconsiderationandsimplifyingthestoringandforwardingofroutesandrequests

Storingroutes

ToaddressthefirstlimitationofthedefaultrouterweneedtobeabletosupportdynamicURLparametersForthesecondandthirdpointsweadoptanalternativeapproachmappingRESTmethodstostructmethodsandroutingrequeststothisstructinsteadoftohandlerfunctionsThiswayaforwardedrequestcanbehandledaccordingtoitsHTTPmethod

BasedontheaboveideaswevedesignedtwodatatypescontrollerInfowhichsavesthepathandthecorrespondingcontrollerTypestructasareflectTypetypeandControllerRegistorwhichsavesroutinginformationforthespecifiedBeegoapplication

typecontrollerInfostruct

regexregexpRegexp

paramsmap[int]string

controllerTypereflectType

typeControllerRegistorstruct

routers[]controllerInfo

ApplicationApp

ControllerRegistorsexternalinterfacecontainsthefollowingmethod

func(pControllerRegistor)Add(patternstringcControllerInterface)

Itsdetailedimplementationisasfollows

Customizedrouters

parts=stringsSplit(pattern)

params=make(map[int]string)

foripart=rangeparts

ifstringsHasPrefix(part)

expr=([^]+)

ausermaychoosetooverridethedefaultexpression

similartoexpressjslsquouserid([0-9]+)rsquo

ifindex=stringsIndex(part()index=-1

expr=part[index]

part=part[index]

params[j]=part

parts[i]=expr

recreatetheurlpatternwithparametersreplaced

byregularexpressionsThencompiletheregex

pattern=stringsJoin(parts)

regexregexErr=regexpCompile(pattern)

ifregexErr=nil

TODOadderrorhandlingheretoavoidpanic

panic(regexErr)

return

nowcreatetheRoute

t=reflectIndirect(reflectValueOf(c))Type()

route=ampcontrollerInfo

routeregex=regex

routeparams=params

routecontrollerType=t

prouters=append(proutersroute)

StaticroutingWeveimplementeddynamicroutinginourexampleaboveBydefaultGoshttppackagesupportsservingstaticfileswithhttpFileServerwhichreturnsaHandlerSincewehaveimplementedacustomrouterwewillalsoneedawayofhandlingstaticfilesBeegosstaticfolderpathissavedinaglobalvariablecalledStaticDirwhichmapstheURLtocorrespondingpathsTheSetStaticPathsimplementationcanbeseenbelow

func(appApp)SetStaticPath(urlstringpathstring)App

StaticDir[url]=path

returnapp

Theapplicationsstaticroutescanbesetlikeso

beegoSetStaticPath(imgstaticimg)

Forwardingroutes

Customizedrouters

WecanforwardroutesbasedontheforwardinginformationcontainedwithinControllerRegistorThedetailedimplementationcanbeseeninthefollowingcodesnippet

AutoRoute

func(pControllerRegistor)ServeHTTP(whttpResponseWriterrhttpRequest)

deferfunc()

iferr=recover()err=nil

ifRecoverPanic

gobacktopanic

panic(err)

Critical(Handlercrashedwitherrorerr)

fori=1i+=1

_filelineok=runtimeCaller(i)

Critical(fileline)

varstartedbool

forprefixstaticDir=rangeStaticDir

ifstringsHasPrefix(rURLPathprefix)

file=staticDir+rURLPath[len(prefix)]

httpServeFile(wrfile)

started=true

return

requestPath=rURLPath

findamatchingRoute

for_route=rangeprouters

checkifRoutepatternmatchesurl

ifrouteregexMatchString(requestPath)

continue

getsubmatches(params)

matches=routeregexFindStringSubmatch(requestPath)

doublecheckthattheRoutematchestheURLpattern

iflen(matches[0])=len(requestPath)

continue

params=make(map[string]string)

iflen(routeparams)gt0

addurlparameterstothequeryparammap

values=rURLQuery()

forimatch=rangematches[1]

valuesAdd(routeparams[i]match)

params[routeparams[i]]=match

reassemblequeryparamsandaddtoRawQuery

rURLRawQuery=urlValues(values)Encode()+amp+rURLRawQuery

rURLRawQuery=urlValues(values)Encode()

Invoketherequesthandler

vc=reflectNew(routecontrollerType)

init=vcMethodByName(Init)

in=make([]reflectValue2)

ct=ampContextResponseWriterwRequestrParamsparams

in[0]=reflectValueOf(ct)

in[1]=reflectValueOf(routecontrollerTypeName())

initCall(in)

Customizedrouters

method=vcMethodByName(Prepare)

methodCall(in)

ifrMethod==GET

method=vcMethodByName(Get)

methodCall(in)

elseifrMethod==POST

method=vcMethodByName(Post)

methodCall(in)

elseifrMethod==HEAD

method=vcMethodByName(Head)

methodCall(in)

elseifrMethod==DELETE

method=vcMethodByName(Delete)

methodCall(in)

elseifrMethod==PUT

method=vcMethodByName(Put)

methodCall(in)

elseifrMethod==PATCH

method=vcMethodByName(Patch)

methodCall(in)

elseifrMethod==OPTIONS

method=vcMethodByName(Options)

methodCall(in)

ifAutoRender

method=vcMethodByName(Render)

methodCall(in)

method=vcMethodByName(Finish)

methodCall(in)

started=true

ifnomatchestourlthrowanotfoundexception

ifstarted==false

httpNotFound(wr)

GettingstartedUsingourrouterdesignwecansolvethethreelimitationsmentionedearlierThethreemainuse-casesare

Registeringroutehandlers

beegoBeeAppRegisterController(ampcontrollersMainController)

Handlingdynamicparameters

beegoBeeAppRegisterController(paramampcontrollersUserController)

Regexmatching

beegoBeeAppRegisterController(usersuid([0-9]+)ampcontrollersUserController)

LinksDirectoryPrevioussectionProjectplanningNextsectionDesigningcontrollers

Customizedrouters

133DesigningcontrollersMosttraditionalMVCframeworksarebasedonsuffixactionmappingNowadaystheRESTstylewebarchitectureisbecomingincreasinglypopularOnecanimplementREST-styleURLsbyfilteringorrewritingthembutwhynotjustdesignanewREST-styleMVCframeworkinsteadThissectionisbasedonthisideaandfocusesondesigningandimplementingacontrollerbasedREST-styleMVCframeworkfromscratchOurgoalistosimplifythedevelopmentofwebapplicationsperhapsevenallowingustowriteasinglelineofcodecapableofservingHelloworld

ThecontrollersroleTheMVCdesignpatterniscurrentlythemostusedframeworkmodelforwebapplicationsBykeepingModelsViewsandControllersseparatedwecankeepourwebapplicationsmodularmaintainabletestableandextensibleAmodelencapsulatesdataandanyofthebusinesslogicthatgovernsthatdatasuchasaccessibilityrulespersistencevalidationetcViewsserveasthedatasrepresentationandinthecaseofwebapplicationstheyusuallyliveastemplateswhicharethenrenderedintoHTMLandservedControllersserveasthegluelogicbetweenModelsandViewsandtypicallyhavemethodsforhandlingdifferentURLsAsdescribedintheprevioussectionwhenaURLrequestisforwardedtoacontrollerbytherouterthecontrollerdelegatescommandstotheModeltoperformsomeactionthennotifiestheViewofanychangesIncertaincasesthereisnoneedformodelstoperformanykindoflogicalordataprocessingorforanyviewstoberenderedForinstanceinthecaseofanHTTP302redirectnoviewneedstoberenderedandnoprocessingneedstobeperformedbytheModelhowevertheControllersjobisstillessential

RESTfuldesigninBeegoTheprevioussectiondescribesregisteringroutehandlerswithRESTfulstructsNowweneedtodesignthebaseclassforalogiccontrollerthatwillbecomposedoftwopartsastructandinterfacetype

typeControllerstruct

CtContext

TpltemplateTemplate

Datamap[interface]interface

ChildNamestring

TplNamesstring

Layout[]string

TplExtstring

typeControllerInterfaceinterface

Init(ctContextcnstring)Initializethecontextandsubclassname

Prepare()someprocessingbeforeexecutionbegins

Get()method=GETprocessing

Post()method=POSTprocessing

Delete()method=DELETEprocessing

Put()method=PUThandling

Head()method=HEADprocessing

Patch()method=PATCHtreatment

Options()method=OPTIONSprocessing

Finish()executedaftercompletionoftreatment

Render()errormethodexecutedafterthecorrespondingmethodtorenderthepage

ThenaddtheroutehandlingfunctiondescribedearlierinthischapterWhenarouteisdefinedtobeaControllerInterfacetypesolongaswecanimplementthisinterfacewecanhaveaccesstothefollowingmethodsofourbaseclasscontroller

func(cController)Init(ctContextcnstring)

cData=make(map[interface]interface)

cLayout=make([]string0)

Designcontrollers

cTplNames=

cChildName=cn

cCt=ct

cTplExt=tpl

func(cController)Prepare()

func(cController)Finish()

func(cController)Get()

httpError(cCtResponseWriterMethodNotAllowed405)

func(cController)Post()

func(cController)Delete()

func(cController)Put()

func(cController)Head()

func(cController)Patch()

func(cController)Options()

func(cController)Render()error

iflen(cLayout)gt0

varfilenames[]string

for_file=rangecLayout

filenames=append(filenamespathJoin(ViewsPathfile))

terr=templateParseFiles(filenames)

iferr=nil

Trace(templateParseFileserrerr)

err=tExecuteTemplate(cCtResponseWritercTplNamescData)

iferr=nil

Trace(templateExecuteerrerr)

ifcTplNames==

cTplNames=cChildName++cCtRequestMethod++cTplExt

terr=templateParseFiles(pathJoin(ViewsPathcTplNames))

iferr=nil

err=tExecute(cCtResponseWritercData)

iferr=nil

returnnil

Designcontrollers

func(cController)Redirect(urlstringcodeint)

cCtRedirect(codeurl)

AbovethecontrollerbaseclassalreadyimplementsthefunctionsdefinedintheinterfaceThroughourroutingrulestherequestwillberoutedtotheappropriatecontrollerwhichwillinturnexecutethefollowingmethods

Init()initializationroutine

Prepare()pre-initializationroutineeachinheritingsubclassmayimplementthisfunction

method()dependingontherequestmethodperformdifferentfunctionsGETPOSTPUTHEADetcSubclassesshouldi

mplementthesefunctionsifnotimplementedthenthedefaultis403

Render()optionalmethodDeterminewhetherornottoexecuteaccordingtotheglobalvariableAutoRender

Finish()isexecutedaftertheactionbeencompletedEachinheritingsubclassmayimplementthisfunction

ApplicationguideAbovewevejustfinisheddiscussingBeegosimplementationofthebasecontrollerclassWecannowusethisinformationtodesignourrequesthandlinginheritingfromthebaseclassandimplementingthenecessarymethodsinourowncontroller

packagecontrollers

import(

githubcomastaxiebeego

typeMainControllerstruct

beegoController

func(thisMainController)Get()

thisData[Username]=astaxie

thisData[Email]=astaxiegmailcom

thisTplNames=indextpl

InthecodeaboveweveimplementedasubclassofControllercalledMainControllerwhichonlyimplementstheGet()methodIfausertriestoaccesstheresourceusinganyoftheotherHTTPmethods(POSTHEADetc)a403ForbiddenwillbereturnedHoweverifausersubmitsaGETrequesttotheresourceandwehavetheAutoRendervariablesettotruetheresourcescontrollerwillautomaticallycallitsRender()functionrenderingthecorrespondingtemplateandrespondingwiththefollowing

Theindextplcodecanbeseenbelowasyoucanseeparsingmodeldataintoatemplateisquitesimple

ltDOCTYPEhtmlgt

lthtmlgt

ltheadgt

lttitlegtbeegowelcometemplatelttitlegt

ltheadgt

ltbodygt

lth1gtHelloworldUsernameEmaillth1gt

ltbodygt

lthtmlgt

LinksDirectory

Designcontrollers

PrevioussectionCustomizingroutersNextsectionLogsandconfigurations

Designcontrollers

134Loggingandconfiguration

TheimportanceofloggingandconfigurationPreviouslyinthebookwesawthateventloggingplaysaveryimportantroleinapplicationdevelopmentWithadequateloggingwecanrecordcrucialinformationthatcanlaterbedissectedfordebuggingandoptimizationpurposesInthesectionwherewelookedattheseelogloggingutilitywesawthatithadsettingsforvariousloglevelgradationswhichcanbeessentialforprogramdevelopmentanddeploymentwecansetthelogginglevellowerinadevelopmentenvironmentwhilesettingithighinproductionsothatwecanmaskextraneousinformationwhenwearetryingtodebugourapplication

SettinguptheserverconfigurationmodulefordeployinganapplicationinvolvesanumberofdifferentserversettingsForexamplewetypicallyneedtoprovideinformationregardingdatabaseconfigurationlisteningportsetcviatheconfigurationfileSettingupacentralizedconfigurationfileallowsustheflexibilityofdeployingtheapplicationtodifferentmachinesandconnectingtoremotedatabasesifneeded

TheBeegologgingsystemTheBeegologgersdesignborrowsideasfromseelogandprovidessimilarfunctionalityintermsofsettinglogginglevelsBeegossystemishowevermorelightweightandmakesuseoftheGoslogLoggerinterfaceBydefaultlogsareoutputtoosStdoutbutuserscanimplementthisinterfacethroughbeegoSetLoggertocustomizethisAdetailedexampleofanimplementedinterfacecanbeseenbelow

Loglevelsforcontrollingtheloggingoutput

const(

LevelTrace=iota

LevelDebug

LevelInfo

LevelWarning

LevelError

LevelCritical

logLevelcontrolsthegloballoglevelusedbythelogger

varlevel=LevelTrace

LogLevelreturnsthegloballoglevelandcanbeusedin

acustomimplementationsoftheloggerinterface

funcLevel()int

returnlevel

SetLogLevelsetsthegloballoglevelusedbythesimple

logger

funcSetLevel(lint)

level=l

ThissectionimplementstheaboveloggradingsystemThedefaultlevelissettoTraceanduserscancustomizegradinglevelsusingSetLevel

loggerreferencestheusedapplicationlogger

varBeeLogger=logNew(osStdoutlogLdate|logLtime)

SetLoggersetsanewlogger

funcSetLogger(llogLogger)

BeeLogger=l

Tracelogsamessageattracelevel

funcTrace(vinterface)

iflevellt=LevelTrace

BeeLoggerPrintf([T]vnv)

Debuglogsamessageatdebuglevel

funcDebug(vinterface)

iflevellt=LevelDebug

BeeLoggerPrintf([D]vnv)

Infologsamessageatinfolevel

funcInfo(vinterface)

iflevellt=LevelInfo

BeeLoggerPrintf([I]vnv)

Warninglogsamessageatwarninglevel

funcWarn(vinterface)

iflevellt=LevelWarning

BeeLoggerPrintf([W]vnv)

Errorlogsamessageaterrorlevel

funcError(vinterface)

iflevellt=LevelError

BeeLoggerPrintf([E]vnv)

Criticallogsamessageatcriticallevel

funcCritical(vinterface)

iflevellt=LevelCritical

BeeLoggerPrintf([C]vnv)

ThecodesnippetaboveinitializesaBeeLoggerobjectbydefaultoutputtinglogstoosStdoutAsmentioneduserscanimplementbeegoSetLoggertocustomizetheloggersoutputBeeLoggerimplementssixfunctions

Trace(recordgeneralinformationforexample)EnteredparsefunctionvalidationblockValidationenteredsecondifDictionaryDictisemptyUsingdefaultvalue

Debug(debugginginformationforexample)WebpagerequestedhttpsomesitecomParams=ResponsegeneratedResponsesize10000SendingNewfilereceivedTypePNGSize20000

Info(printinggeneralinformationforexample)WebserverrestartedHourlystatisticsRequestedpages12345Errors123ServicepausedWaitingforresumecall

Warn(warningmessagesforexample)Cachecorruptedforfile=testfileReadingfromback-endDatabase19216807DBnotrespondingUsingbackup19216808DBNoresponsefromstatisticsserverStatisticsnotsent

Error(errormessagesforexample)InternalerrorCannotprocessrequest12345ErrorCannotperformlogincredentialsDBnotresponding

Critical(fatalerrorsforexample)CriticalpanicreceivedShuttingdownFatalerrorAppisshuttingdowntopreventdatacorruptionorloss

YoucanseethateachoftheselevelshasaspecificpurposeForinstanceifwesettheloggingleveltoWarn(level=LevelWarning)atthetimeofdeploymentallofthelowerlevellogs(TraceDebugInfo)willnotoutputanything

BeegoconfigurationdesignForprocessingconfigurationinformationBeegoimplementsakey=valuefileparserwhichreadsinformationformattedsimilarlytoiniconfigurationfilesTheparserreadstheconfigurationdataandsavesittoamapFinallyitcallsseveralfunctionsforretrievingthevaluesdatatype(intstringetc)Thedetailedimplementationcanbeseenbelow

Definesomeglobalconstantsfortheiniconfigurationfile

bComment=[]byte

bEmpty=[]byte

bEqual=[]byte=

bDQuote=[]byte

Definestheformatoftheconfigurationfile

AConfigrepresentstheconfiguration

typeConfigstruct

filenamestring

commentmap[int][]stringid[]commentkeyid1isformaincomment

datamap[string]stringkeyvalue

offsetmap[string]int64keyoffsetforediting

syncRWMutex

DefinesafunctionforparsingthefileTheprocessbeginsbyopeningthefilethenreadingitlinebylineandparsingcommentsblanklinesandkey=valuedata

ParseFilecreatesanewConfigandparsesthefileconfigurationfromthe

namedfile

funcLoadConfig(namestring)(Configerror)

fileerr=osOpen(name)

iferr=nil

returnnilerr

cfg=ampConfig

fileName()

make(map[int][]string)

make(map[string]string)

make(map[string]int64)

syncRWMutex

cfgLock()

defercfgUnlock()

deferfileClose()

varcommentbytesBuffer

buf=bufioNewReader(file)

fornCommentoff=0int64(1)

line_err=bufReadLine()

iferr==ioEOF

ifbytesEqual(linebEmpty)

continue

off+=int64(len(line))

ifbytesHasPrefix(linebComment)

line=bytesTrimLeft(line)

line=bytesTrimLeftFunc(lineunicodeIsSpace)

commentWrite(line)

commentWriteByte(n)

continue

ifcommentLen()=0

cfgcomment[nComment]=[]stringcommentString()

commentReset()

nComment++

val=bytesSplitN(linebEqual2)

ifbytesHasPrefix(val[1]bDQuote)

val[1]=bytesTrim(val[1]``)

key=stringsTrimSpace(string(val[0]))

cfgcomment[nComment-1]=append(cfgcomment[nComment-1]key)

cfgdata[key]=stringsTrimSpace(string(val[1]))

cfgoffset[key]=off

returncfgnil

BelowareanumberoffunctionstheparserusesforreadingtheconfigurationfileThereturnvalueisdeterminedaseitheraboolintfloat64orstring

Boolreturnsthebooleanvalueforagivenkey

func(cConfig)Bool(keystring)(boolerror)

returnstrconvParseBool(cdata[key])

Intreturnstheintegervalueforagivenkey

func(cConfig)Int(keystring)(interror)

returnstrconvAtoi(cdata[key])

Floatreturnsthefloatvalueforagivenkey

func(cConfig)Float(keystring)(float64error)

returnstrconvParseFloat(cdata[key]64)

Stringreturnsthestringvalueforagivenkey

func(cConfig)String(keystring)string

returncdata[key]

ApplicationguideThefollowingfunctionisanexampleofanapplicationIusedtofetchjsondatafromaremoteurladdress

funcGetJson()

resperr=httpGet(beegoAppConfigString(url))

iferr=nil

beegoCritical(httpgetinfoerror)

return

err=jsonUnmarshal(bodyampAllInfo)

iferr=nil

beegoCritical(errorerr)

BeegosCritical()loggingfunctioniscalledtoreportanyerrorswhichmayoccurintheGetJson()functionbeegoAppConfigString(url)isusedtoobtaininformationfromaconfigurationfile(typicallyappconf)whichmightlooksomethinglikethefollowing

appname=hs

url=httpwwwapicomapihtml

LinksDirectoryPrevioussectionDesigningcontrollersNextsectionAddingdeletingandupdatingblogs

135AddingdeletingandupdatingblogsWevealreadyintroducedtheentireconceptbehindtheBeegoframeworkthroughexamplesandpseudo-codeThissectionwilldescribehowtoimplementabloggingsystemusingBeegoincludingtheabilitytobrowseaddmodifyanddeleteblogposts

BlogdirectoryOurblogsdirectorystructurecanbeseenbelow

maingo

viewtpl

newtpl

layouttpl

indextpl

edittpl

modelsmodelgo

controllers

indexgo

viewgo

deletego

editgo

BlogroutingOurblogsmainroutingrulesareasfollows

ShowblogHome

beegoRegisterController(ampcontrollersIndexController)

Viewblogdetails

beegoRegisterController(viewid([0-9]+)ampcontrollersViewController)

CreateblogBowen

beegoRegisterController(newampcontrollersNewController)

DeleteBowen

beegoRegisterController(deleteid([0-9]+)ampcontrollersDeleteController)

EditBowen

beegoRegisterController(editid([0-9]+)ampcontrollersEditController)

DatabasestructureAtrivialdatabasetabletostorebasicbloginformation

CREATETABLEentries(

idINTAUTO_INCREMENT

titleTEXT

contentTEXT

createdDATETIME

primarykey(id)

ControllerIndexController

typeIndexControllerstruct

beegoController

func(thisIndexController)Get()

thisData[blogs]=modelsGetAll()

thisLayout=layouttpl

ViewController

typeViewControllerstruct

beegoController

func(thisViewController)Get()

inputs=thisInput()

id_=strconvAtoi(thisCtxParams[id])

thisData[Post]=modelsGetBlog(id)

thisTplNames=viewtpl

NewController

typeNewControllerstruct

beegoController

func(thisNewController)Get()

thisTplNames=newtpl

func(thisNewController)Post()

inputs=thisInput()

varblogmodelsBlog

blogTitle=inputsGet(title)

blogContent=inputsGet(content)

blogCreated=timeNow()

modelsSaveBlog(blog)

thisCtxRedirect(302)

EditController

typeEditControllerstruct

beegoController

func(thisEditController)Get()

inputs=thisInput()

thisTplNames=edittpl

func(thisEditController)Post()

inputs=thisInput()

varblogmodelsBlog

blogId_=strconvAtoi(inputsGet(id))

DeleteController

typeDeleteControllerstruct

beegoController

func(thisDeleteController)Get()

id_=strconvAtoi(thisCtxInputParams[id])

blog=modelsGetBlog(id)

thisData[Post]=blog

modelsDelBlog(blog)

Modellayer

packagemodels

import(

databasesql

typeBlogstruct

Idint`PK`

Titlestring

Contentstring

CreatedtimeTime

funcGetLink()beedbModel

dberr=sqlOpen(mymysqlblogastaxie123456)

iferr=nil

panic(err)

orm=beedbNew(db)

returnorm

funcGetAll()(blogs[]Blog)

db=GetLink()

dbFindAll(ampblogs)

return

funcGetBlog(idint)(blogBlog)

db=GetLink()

dbWhere(id=id)Find(ampblog)

return

funcSaveBlog(blogBlog)(bgBlog)

db=GetLink()

dbSave(ampblog)

returnbg

funcDelBlog(blogBlog)

db=GetLink()

dbDelete(ampblog)

return

Viewlayerlayouttpl

lthtmlgt

ltheadgt

lttitlegtMyBloglttitlegt

ltstylegt

width200px

floatright

ltstylegt

ltheadgt

ltbodygt

ltulid=menugt

ltligtltahref=gtHomeltagtltligt

ltligtltahref=newgtNewPostltagtltligt

ltulgt

LayoutContent

ltbodygt

lthtmlgt

indextpl

lth1gtBlogpostslth1gt

ltulgt

rangeblogs

ltligt

ltahref=viewIdgtTitleltagt

fromCreated

ltahref=editIdgtEditltagt

ltahref=deleteIdgtDeleteltagt

ltligt

ltulgt

viewtpl

lth1gtPostTitlelth1gt

PostCreatedltbrgt

PostContent

newtpl

lth1gtNewBlogPostlth1gt

ltformaction=method=postgt

Titleltinputtype=textname=titlegtltbrgt

Contentlttextareaname=contentcolspan=3rowspan=10gtlttextareagt

ltformgt

edittpl

lth1gtEditPostTitlelth1gt

Titleltinputtype=textname=titlevalue=PostTitlegtltbrgt

Contentlttextareaname=contentcolspan=3rowspan=10gtPostContentlttextareagt

ltinputtype=hiddenname=idvalue=PostIdgt

ltformgt

LinksDirectoryPrevioussectionLogsandconfigurationsNextsectionSummary

136SummaryInthischapterwedescribedhowtoimplementthemajorcomponentsofaGowebframeworkWefirstdesignedaroutertomakeupforsomeofshortcomingsinGosbuilt-inhttppackagecreatingaroutercapableofdynamicroutingandRESTsupportWealsodesignedourownRESTfulControllerclassinaccordwiththeprinciplesofMVCborrowingideasfromframeworkssuchasTornadoNextwedesignedandimplementedatemplatelayoutandautomatedrenderingsystemmainlyusingGosbuilt-intemplatingengineWethenimplementedacustomloggerandtalkedaboutframeworkconfigurationtoallowforflexibleapplicationdeploymentThroughthisprocesswehaveimplementedabasicwebframeworkcalledBeegowhichatpresenthasbeenopen-sourcedonGithubLastlyweimplementedasimplebloggingapplicationontopofBeegoAfterhavinggonethroughalloftheseexamplesyouwillhopefullyhavelearnedhowtoquicklydevelopwebsitesinGo

LinksDirectoryPrevioussectionAdddeleteandupdateblogsNextchapterDevelopwebframework

Summary

14DevelopingawebframeworkChapter13describedhowtodevelopawebframeworkinGoWeintroducedtheMVCarchitecturearoutingandloggingsystemandwealsolookedatsimpleserverconfigurationThesearethebasicbuildingblocksofmostframeworksanditsagoodstartHoweverformoresophisticatedneedssomeauxiliarytoolsareneededtofacilitaterapidwebsitedevelopmentInthischapterwewillprovidesomequicktipsandtoolsforspeedingupdevelopmentThefirstsectionwillcoverthehow-toshowprocessingstaticfilesandwewillbeusingTwittersopensourceCSSandJavascriptframeworkcalledBootstrapforbeautifyingourwebsiteThesecondsectiondescribeshowtousethepreviouslydescribedsessionsforuserloginprocessingNextthethirdsectiondescribeshowtogenerateformsandhowtoprocesstheseformsforvaliddataWewillalsotalkabouthowtobindmodelsforCRUDoperationsInsection4welldescribehowtoperformsomeuserauthenticationincludingbasicHTTPauthenticationandHTTPdigestauthenticationFinallythelastsectionwilltalkaboutimplementingthepreviouslydescribedi18ntosupportmulti-lingualwebapplications

ByextendingBeegointhischapterwewillbeabletorapidlydevelopfullstackwebapplicationsOfcoursewellgothroughthefeaturesoftheseextensionsstep-by-stepapplyingthemtothebloggingsystemwedevelopedinChapter13ThroughthedevelopmentofacompleteandbeautifulbloggingsystemuserswillhopefullybeabletoseehowBeegocanhelptoboostdeveloperproductivity

LinksDirectoryPreviouschapterChapter13summaryNextsectionStaticfiles

Developwebframework

141StaticfilesWevealreadytalkedabouthowtodealwithstaticfilesinprevioussectionsNowletslookathowtosetupandusestaticfilesinsideofBeegoThenthroughintroducingTwittersopensourceHTMLandCSSframeworkBootstrapwellbeablequicklycreatebeautifullookingwebsiteswithouthavingtodotoomuchdesignwork

BeegostaticfilesandsettingsGosnethttppackageprovidesastaticfileserverwithfunctionssuchasServeFileandFileServerBeegosstaticfilehandlingisbasedonthislayeranditsspecificimplementationisasfollow

staticfileserver

wstarted=true

return

StaticDirstorestheURLwhichcorrespondstoastaticfiledirectorysowhenhandlingrequestswesimplyneedtodeterminewhetherornottheURLbeginswithastaticfilepathIfsowecansimplyrespondusinghttpServeFile

Thefollowingisanexample

beegoStaticDir[asset]=static

ThenarequestwithaURLsuchashttpwwwbeegomeassetbootstrapcsswillresultinstaticbootstrapcssbeingservedtotheclient

BootstrapintegrationBootstrapisanopensourceToolkitforfront-enddevelopmentlaunchedbyTwitterFordevelopersBootstrapisoneofthebestfrontendkitsforrapidWebapplicationdevelopmentItisacollectionofHTMLCSSandjavascriptcomponentsusingthelatestHTML5standardsTheseincludearesponsivegridformsbuttonstablesandmanyotherusefulthings

ComponentsBootstrapcontainsawealthofWebcomponentsUsingthesecomponentsyoucanquicklybuildabeautifulfullyfunctionalwebsitewhichincludesthefollowingcomponentsPull-downmenusbuttongroupsbuttondrop-downmenusnavigationnavigationbarsbreadcrumbspaginationlayoutthumbnailswarningdialogsprogressbarsandothermediaobjectsJavaScriptpluginsBootstrapcomeswith13jQueryplug-insforBootstrapcomponentswhichgivesthemlifeTheseincludeModaldialogstabsscrollbarspop-upboxesandsoonBootstrapframeworkcustomizationAllBootstrapcssvariablescanbemodifiedaccordingtoyourneeds

Figure141abootstrapwebsite

NextletsseehowwecanuseBootstrapinsideourBeegoapplicationtoquicklycreateabeautifulwebsite

1 Firstletsdownloadthebootstrapdirectoryintoourprojectsstaticdirectoryasshowninthefollowingscreenshot

Staticfiles

Figure142Projectstaticfiledirectorystructure

2 BecauseBeegosetsadefaultvalueforStaticDirifyourstaticfilesdirectoryisstaticthenyouneednotgoanyfurther

StaticDir[static]=static

3 Ourtemplatesusethefollowingassetpaths

cssfile

ltlinkhref=staticcssbootstrapcssrel=stylesheetgt

jsfile

ltscriptsrc=staticjsbootstrap-transitionjsgtltscriptgt

Picturefiles

ltimgsrc=staticimglogopnggt

WiththeabovecodeweareintegratingBootstrapintoourBeegoapplicationThefigurebelowdemonstratestherenderedpage

Figure143websiteintegratedwithBootstrap

ThesetemplatesandformatsallcomeshippedwithBootstrapsowewontrepeatthecompletecodeherehoweveryoucantakealookattheprojectsofficialpagetolearnhowtowriteyourowntemplates

LinksDirectoryPrevioussectionDevelopingawebframeworkNextsectionSessions

Staticfiles

142SessionsInchapter6weintroducedsomebasicconceptspertainingtosessionsinGoandweimplementedasessionmanagerTheBeegoframeworkusesthissessionmanagertoimplementsomeconvenientsession-handlingfunctionality

IntegratingsessionsBeegohandlessessionsmainlyaccordingtothefollowingglobalvariables

relatedtosession

SessionOnboolwhetherornottoopenthesessionmoduleDefaultstofalse

SessionProviderstringthedesiredsessionbackendprocessingmoduleDefaultstoanin-memorysessionManager

SessionNamestringthenameoftheclientsavedcookies

SessionGCMaxLifetimeint64cookievalidity

GlobalSessionssessionManagerglobalsessioncontroller

OfcoursethevaluesofthesevariablesshownaboveneedtobeinitializedYoucanalsousethevaluesfromthefollowingconfigurationfilecodetosetthesevalues

ifarerr=AppConfigBool(sessionon)err=nil

SessionOn=false

SessionOn=ar

ifar=AppConfigString(sessionprovider)ar==

SessionProvider=memory

SessionProvider=ar

ifar=AppConfigString(sessionname)ar==

SessionName=beegosessionID

SessionName=ar

ifarerr=AppConfigInt(sessiongcmaxlifetime)err=nilampampar=0

int64val_=strconvParseInt(strconvItoa(ar)1064)

SessionGCMaxLifetime=int64val

SessionGCMaxLifetime=3600

AddthefollowingcodeinthebeegoRunfunction

ifSessionOn

GlobalSessions_=sessionNewManager(SessionProviderSessionNameSessionGCMaxLifetime)

goGlobalSessionsGC()

AslongasSessionOnissettotrueitwillopenthesessionbydefaultwithanindependentgoroutinesessionhandler

InordertofacilitateourcustomControllerquicklyusingsessiontheauthorbeegoControllerprovidesthefollowingmethods

ToassistusinquicklyusingsessionsinacustomControllerbeegoControllerprovidesthefollowingmethod

Session

func(cController)StartSession()(sesssessionSession)

sess=GlobalSessionsSessionStart(cCtxResponseWritercCtxRequest)

return

UsingsessionsFromthecodeabovewecanseethattheBeegoframeworksimplyinheritsitssessionfunctionalitySohowdoweuseitinourprojects

Firstofallweneedtoopenthesessionattheentrypointofourapplication

beegoSessionOn=true

Wecanthenusethecorrespondingsessionmethodinsideourcontrollerlikeso

varintcountint

sess=thisStartSession()

count=sessGet(count)

ifcount==nil

intcount=0

intcount=count(int)

intcount=intcount+1

sessSet(countintcount)

thisData[Count]=intcount

ThecodeaboveshowshowtousesessionsinthecontrollerlogicTheprocesscanbedividedintotwosteps

1 Gettingsessionobject

GettheobjectsimilarinPHPsession_start()

2 Usingthesessionforgeneraloperations

GetthesessionvaluessimilarinPHP$_SESSION[count]

sessGet(count)

Setthesessionvalue

AsyoucanseeapplicationsbasedontheBeegoframeworkcaneasilyimplementsessionsTheprocessisverysimilartocallingsession_start()inPHPapplications

LinksDirectoryPrevioussectionStaticfilesNextsectionForms

Session

143FormsInwebdevelopmentthefollowingworkflowwillprobablylookquitefamiliar

OpenawebpageshowingaformUsersfilloutandsubmittheformIfausersubmitssomeinvalidinformationorhasneglectedtofilloutarequiredfieldtheformwillbereturnedtotheuser(alongwiththefilledindata)withsomedescriptiveinformationabouttheproblemUsersre-filltheinvalidfieldsandcontinueattemptingtosubmittheformuntilitsaccepted

Atthereceivingendthescriptmust

ChecktheusersubmittedformdataVerifywhetherthedataisthecorrecttypeandoftheappropriatestandardForexampleifausernameissubmitteditmustverifythatitcontainsonlyvalidcharactersOtherexampleswouldbecheckingforminimumandmaximumlengthsusernameuniquenessandsoonFilteringdataandcleaningupunsafecharacterstoguaranteethatourapplicationonlyprocessesdatawhichissafeIfnecessarypre-formatthedata(ordatagapsneedtobeclearedthroughtheHTMLcodingandsoon)Preparethedataforinsertionintothedatabase

AlthoughtheprocedureisnotverycomplexitusuallyrequiresalotofboilerplateInadditionwebapplicationsoftenuseavarietyofdifferentcontrolstructurestodisplayerrormessagesonreturnedpagesImplementingformvalidationisasimplebutboringtask

FormsandvalidationFordevelopersthegeneraldevelopmentprocesscanbequitecomplexbutitsmostlyrepetitiveworkSupposeascenarioariseswhereyousuddenlyneedtoaddaformtoyourprojectcausingyoutorewriteallofthelocalcodetiedinwiththeformWeknowthatstructsareaverycommonlyuseddatastructureinGoandBeegousesthemtoitsadvantageforprocessingforminformation

FirstwedefineastructwithfieldscorrespondingtothefieldsinourformelementWecanusestructtagswhichmaptotheformelementasshownbelow

WhendevelopingWebapplicationsfirstdefineastructthatmatchesafieldtoacorrespondingformelementdefinedbyusingastructtagcorrespondingtotheelementinformationandauthenticationinformationasshownbelow

FordevelopersthegeneraldevelopmentprocessisverycomplexandmostlyconsistsofrepeatingthesameworkprocessAssumingascenarioforaprojectwherebyaneedarisestoadddatatoaformthenthelocalcodeoftheentireprocessneedstobemodifiedWeknowinGoastructisacommondatastructuresobeegousesaformstructtoprocessforminformation

Firstdefineastructwithfieldscorrespondingtoourformelementusingstructtagstodefinethecorrespondingformelementandauthenticationinformationlikeso

typeUserstruct

Usernamestring`formtextvalidrequired`

Nicknamestring`formtextvalidrequired`

Ageint`formtextvalidrequired|numeric`

Emailstring`formtextvalidrequired|valid_email`

Introducestring`formtextarea`

Afterdefiningourstructwecanaddthisactioninourcontroller

func(thisAddController)Get()

thisData[form]=beegoForm(ampUser)

thisLayout=adminlayouthtml

thisTplNames=adminaddtpl

Theformisdisplayedinourtemplatelikeso

formrender()

ltformgt

AbovewevedefinedtheentirefirststepofdisplayingaformmappedtoastructThenextstepisforuserstofillintheirinformationandsubmittheformafterwhichtheserverwillreceivethedataandverifyitFinallytherecordwillbeinsertedintothedatabase

func(thisAddController)Post()

varuserUser

form=thisGetInput(ampuser)

ifformValidates()

return

modelsUserInsert(ampuser)

thisCtxRedirect(302adminindex)

FormtypeThefollowingtableliststhecorrespondingformelementinformation

lttablecellpadding=0cellspacing=1border=0style=width100class=tablebordergt

lttbodygt

lttrgt

ltthgtNameltthgt

ltthgtparameterltthgt

ltthgtDescriptionltthgt

lttrgt

lttdclass=tdgtltstronggttextltstronggt

lttdgt

lttdclass=tdgtNolttdgt

lttdclass=tdgttextboxinputboxlttdgt

lttrgt

lttdclass=tdgtltstronggtbuttonltstronggt

lttdgt

lttdclass=tdgtbuttonlttdgt

lttrgt

lttdclass=tdgtltstronggtcheckboxltstronggt

lttdgt

lttdclass=tdgtmulti-selectboxlttdgt

lttrgt

lttdclass=tdgtltstronggtdropdownltstronggt

lttdgt

lttdclass=tdgtdrop-downselectionboxlttdgt

lttrgt

lttdclass=tdgtltstronggtfileltstronggt

lttdgt

lttdclass=tdgtfileuploadlttdgt

lttrgt

lttdclass=tdgtltstronggthiddenltstronggt

lttdgt

lttdclass=tdgthiddenelementslttdgt

lttrgt

lttdclass=tdgtltstronggtpasswordltstronggt

lttdgt

lttdclass=tdgtpasswordinputboxlttdgt

lttrgt

lttdclass=tdgtltstronggtradioltstronggt

lttdgt

lttdclass=tdgtsingleboxlttdgt

lttrgt

lttdclass=tdgtltstronggttextarealtstronggt

lttdgt

lttdclass=tdgttextinputboxlttdgt

lttrgt

lttbodygt

lttablegt

FormvalidationThefollowingtablelistssomeformvalidationrulesnativetoBeegothatcanbeused

lttbodygt

lttrgt

ltthgtrulesltthgt

ltthgtExampleltthgt

lttrgt

lttdclass=tdgtltstronggtrequiredltstronggt

lttdgt

lttdclass=tdgtIftheelementisemptyitreturnsFALSElttdgt

lttdclass=tdgtlttdgt

lttrgt

lttdclass=tdgtltstronggtmatchesltstronggt

lttdgt

lttdclass=tdgtYeslttdgt

lttdclass=tdgtiftheformelementsvaluewiththecorrespondingformfieldparametervaluesarenotequalth

enreturn

FALSElttdgt

lttdclass=tdgtmatches[form_item]lttdgt

lttrgt

lttdclass=tdgtltstronggtis_uniqueltstronggt

lttdgt

lttdclass=tdgtiftheformelementsvaluewiththespecifiedfieldinatablehasduplicatedataitreturnsF

alse(Translators

NoteForexampleis_unique[UserEmail]thenthevalidationclasswilllookfortheUsertableinthe

Emailfieldthereisnoformelementswiththesamevaluesuchasdepositrepeatitreturnsfalseso

developersdonothavetowriteanotherCallbackverificationcode)lttdgt

lttdclass=tdgtis_unique[tablefield]lttdgt

lttrgt

lttdclass=tdgtltstronggtmin_lengthltstronggt

lttdgt

lttdclass=tdgtformelementvaluesifthecharacterlengthislessthanthenumberofdefinedparametersitre

turnsFALSElttdgt

lttdclass=tdgtmin_length[6]lttdgt

lttrgt

lttdclass=tdgtltstronggtmax_lengthltstronggt

lttdgt

lttdclass=tdgtiftheformelementsvalueisgreaterthanthelengthofthecharacterdefinednumericargument

itreturns

FALSElttdgt

lttdclass=tdgtmax_length[12]lttdgt

lttrgt

lttdclass=tdgtltstronggtexact_lengthltstronggt

lttdgt

lttdclass=tdgtiftheformelementvaluesandparametersdefinedcharacterlengthnumberdoesnotmatchitret

urnsFALSElttdgt

lttdclass=tdgtexact_length[8]lttdgt

lttrgt

lttdclass=tdgtltstronggtgreater_thanltstronggt

lttdgt

lttdclass=tdgtIftheformelementvaluesnon-numerictypesorlessthanthevaluedefinedparametersitret

urnsFALSElttdgt

lttdclass=tdgtgreater_than[8]lttdgt

lttrgt

lttdclass=tdgtltstronggtless_thanltstronggt

lttdgt

lttdclass=tdgtIftheformelementvaluesnon-numerictypesorgreaterthanthevaluedefinedparametersit

returnsFALSElttdgt

lttdclass=tdgtless_than[8]lttdgt

lttrgt

lttdclass=tdgtltstronggtalphaltstronggt

lttdgt

lttdclass=tdgtIftheformelementvaluecontainscharactersotherthanlettersbesidesitreturnsFALSElttdgt

lttrgt

lttdclass=tdgtltstronggtalpha_numericltstronggt

lttdgt

lttdclass=tdgtIftheformelementvaluescontainedinadditiontolettersandothercharactersotherthannumb

ersitreturns

FALSElttdgt

lttrgt

lttdclass=tdgtltstronggtalpha_dashltstronggt

lttdgt

lttdclass=tdgtIftheformelementvaluecontainsinadditiontotheletternumberunderlinecharactersothe

rthandash

returnsFALSElttdgt

lttrgt

lttdclass=tdgtltstronggtnumericltstronggt

lttdgt

lttdclass=tdgtIftheformelementvaluecontainscharactersotherthannumbersinadditionitreturnsFALSElt

lttrgt

lttdclass=tdgtltstronggtintegerltstronggt

lttdgt

lttdclass=tdgtexceptiftheformelementcontainscharactersotherthananintegeritreturnsFALSElttdgt

lttrgt

lttdclass=tdgtltstronggtdecimalltstronggt

lttdgt

lttdclass=tdgtIftheformelementtype(non-decimal)isnotcompleteitreturnsFALSElttdgt

lttrgt

lttdclass=tdgtltstronggtis_naturalltstronggt

lttdgt

lttdclass=tdgtvalueiftheformelementcontainsanumberofotherunnaturalvalues(othervaluesexcludingz

ero)it

returnsFALSENaturalnumberslikethis0123andsoonlttdgt

lttrgt

lttdclass=tdgtltstronggtis_natural_no_zeroltstronggt

lttdgt

lttdclass=tdgtvalueiftheformelementcontainsanumberofotherunnaturalvalues(othervaluesincludingz

ero)it

returnsFALSENonzeronaturalnumbers123andsoonlttdgt

lttrgt

lttdclass=tdgtltstronggtvalid_emailltstronggt

lttdgt

lttdclass=tdgtIftheformelementvaluecontainsinvalidemailaddressitreturnsFALSElttdgt

lttrgt

lttdclass=tdgtltstronggtvalid_emailsltstronggt

lttdgt

lttdclass=tdgtformelementvaluesifanyonevaluecontainsinvalidemailaddress(addressesseparatedbycomm

asinEnglish

)itreturnsFALSElttdgt

lttrgt

lttdclass=tdgtltstronggtvalid_ipltstronggt

lttdgt

lttdclass=tdgtiftheformelementsvalueisnotavalidIPaddressitreturnsFALSElttdgt

lttrgt

lttdclass=tdgtltstronggtvalid_base64ltstronggt

lttdgt

lttdclass=tdgtiftheformelementsvaluecontainsthebase64-encodedcharactersinadditiontootherthanthe

characters

returnsFALSElttdgt

lttrgt

lttbodygt

lttablegt

LinksDirectoryPrevioussectionSessionsNextsectionUservalidation

144UservalidationIntheprocessofdevelopingwebapplicationsuserauthenticationisaproblemwhichdevelopersfrequentlyencounterUserloginregistrationandlogoutamongotheroperationsaswellasgeneralauthenticationcanbedividedintothreeparts

HTTPBasicandHTTPDigestAuthenticationThirdPartyAuthenticationIntegrationQQmicro-bloggingwatercressOPENIDGoogleGitHubFacebookandtwitteretcCustomuserloginregistrationlogoutaregenerallybasedonsessionsandcookieauthentication

BeegodoesnotnativelyprovidesupportforanyofthesethreethingshoweveryoucaneasilymakeuseofexistingthirdpartyopensourcelibrariestoimplementthemThefirsttwoauthenticationsolutionsareonBeegosroadmaptoeventuallybeintegrated

HTTPbasicanddigestauthenticationBothHTTPbasicanddigestauthenticationarerelativelysimpletechniquescommonlyusedbywebapplicationsTherearealreadymanyopensourcethird-partylibrarieswhichsupportthesetwoauthenticationmethodssuchas

githubcomabbotgo-http-auth

ThefollowingcodedemonstrateshowtousethislibrarytoimplementauthenticationinaBeegoapplication

packagecontrollers

import(

funcSecret(userrealmstring)string

ifuser==john

passwordishello

return$1$dlPL2MqE$oQmn16q49SqdmhenQuNgs1

return

beegoController

func(thisMainController)Prepare()

a=authNewBasicAuthenticator(examplecomSecret)

ifusername=aCheckAuth(thisCtxRequest)username==

aRequireAuth(thisCtxResponseWriterthisCtxRequest)

TheabovecodetakesadvantageofBeegosprepare()functiontoperformauthenticationbeforeallowingthenormalflowofexecutiontoproceedasyoucanseeitsverysimpletoimplementHTTPauthenticationDigestauthenticationcanbeimplementedinmuchthesameway

Uservalidation

OAuthandOAuth2authenticationOAuthandOAuth2arecurrentlytwoofthemostpopularauthenticationmethodsFortunatelytherearethird-partylibrarieswhichimplementthistypeofauthenticationsuchasthegoauthpackageavailableongithub

githubcombradrydzewskigoauth

ThecodebelowdemonstrateshowtousethislibrarytoimplementOAuthauthenticationinBeegousingourGithubcredentials

1 Letsaddsomeroutes

beegoRegisterController(authloginampcontrollersGithubController)

beegoRegisterController(mainpageampcontrollersPageController)

2 ThenwedealwiththeGithubControllerlandingpage

packagecontrollers

import(

const(

githubClientKey=a0864ea791ce7e7bd0df

githubSecretKey=a0ec09a647a688a64a28f6190b5a0d2705df56ca

typeGithubControllerstruct

beegoController

func(thisGithubController)Get()

settheauthparameters

authConfigCookieSecret=[]byte(7H9xiimk2QdTdYI7rDddfJeV)

authConfigLoginSuccessRedirect=mainpage

authConfigCookieSecure=false

githubHandler=authGithub(githubClientKeygithubSecretKey)

githubHandlerServeHTTP(thisCtxResponseWriterthisCtxRequest)

3 Handlingafterasuccessfullandingpage

Uservalidation

packagecontrollers

import(

nethttp

neturl

typePageControllerstruct

beegoController

func(thisPageController)Get()

usererr=authGetUserCookie(thisCtxRequest)

ifnoactiveusersessionthenauthorizeuser

iferr=nil||userId()==

httpRedirect(thisCtxResponseWriterthisCtxRequestauthConfigLoginRedirecthttpStatusSeeOther

return

elseaddtheusertotheURLandcontinue

thisCtxRequestURLUser=urlUser(userId())

thisData[pic]=userPicture()

thisData[id]=userId()

thisData[name]=userName()

thisTplNames=hometpl

Thewholeprocessisasfollows

firstopenyourbrowserandentertheaddress

Figure144showsthehomepagewithaloginbutton

Whenclickingonthelinkthefollowingscreenappears

Figure145displayedafterclickingtheloginbuttontoauthenticatewithyourGitHubcredentials

AfterclickingAuthorizeappthefollowingscreenappears

Figure146authorizedGithubinformationgetsdisplayedaftertheloginpage

CustomauthenticationCustomauthenticationisgenerallycombinedwithsessionauthenticationthefollowingcodeisaBeegobasedopensourceblogwhichdemonstratesthis

Loginprocess

func(thisLoginController)Post()

thisTplNames=logintpl

thisCtxRequestParseForm()

username=thisCtxRequestFormGet(username)

Uservalidation

password=thisCtxRequestFormGet(password)

md5Password=md5New()

ioWriteString(md5Passwordpassword)

buffer=bytesNewBuffer(nil)

fmtFprintf(bufferxmd5PasswordSum(nil))

newPass=bufferString()

now=timeNow()Format(2006-01-02150405)

userInfo=modelsGetUserInfo(username)

ifuserInfoPassword==newPass

varusersmodelsUser

usersLast_logintime=now

modelsUpdateUserInfo(users)

Setthesessionsuccessfullogin

sess=globalSessionsSessionStart(thisCtxResponseWriterthisCtxRequest)

sessSet(uiduserInfoId)

sessSet(unameuserInfoUsername)

Registrationprocess

func(thisRegController)Post()

thisTplNames=regtpl

usererr=checkUsername(username)

fmtPrintln(usererr)

ifusererr==false

thisData[UsernameErr]=UsernameerrorPleasetoagain

return

passerr=checkPassword(password)

ifpasserr==false

thisData[PasswordErr]=PassworderrorPleasetoagain

return

ifuserInfoUsername==

varusersmodelsUser

usersUsername=username

usersPassword=newPass

usersCreated=now

modelsAddUser(users)

thisData[UsernameErr]=Useralreadyexists

Uservalidation

funccheckPassword(passwordstring)(bbool)

ifok_=regexpMatchString(^[a-zA-Z0-9]416$password)ok

returnfalse

returntrue

funccheckUsername(usernamestring)(bbool)

ifok_=regexpMatchString(^[a-zA-Z0-9]416$username)ok

returnfalse

returntrue

Onceyouhaveimplementeduserloginandregistrationothermodulescanbeaddedtodeterminewhethertheuserhasbeenloggedinornot

func(thisAddBlogController)Prepare()

sess_uid=sessGet(userid)

sess_username=sessGet(username)

ifsess_uid==nil

thisCtxRedirect(302adminlogin)

return

thisData[Username]=sess_username

LinksDirectoryPrevioussectionFormNextsectionMulti-languagesupport

Uservalidation

145Multi-languagesupportInthechapterwhereweintroducedinternationalizationandlocalizationwedevelopedthego-i18nlibraryInthissectionwewillseehowthislibraryisintegratedintotheBeegoframeworkandhowitenablesourBeegoapplicationstosupportbothinternationalizationandlocalization

I18nintegrationBeegofirstsetssomeglobalvariables

Translationi18nIL

Langstringsetthelanguagepackzhen

LangPathstringsetthelanguagepacklocation

Amulti-languageinitializationfunctionisdefined

funcInitLang()

beegoTranslation=i18nNewLocale()

beegoTranslationLoadPath(beegoLangPath)

beegoTranslationSetLocale(beegoLang)

Inordertofacilitatemulti-languagecallsinthetemplatepackagedirectlywedesignedthreefunctionsforhandlingmulti-languageresponses

beegoTplFuncMap[Trans]=i18nI18nT

beegoTplFuncMap[TransDate]=i18nI18nTimeDate

beegoTplFuncMap[TransMoney]=i18nI18nMoney

ok=false

varsstring

iflen(args)==1

sok=args[0](string)

s=fmtSprint(args)

returnbeegoTranslationTranslate(s)

ok=false

varsstring

iflen(args)==1

sok=args[0](string)

s=fmtSprint(args)

returnbeegoTranslationTime(s)

ok=false

varsstring

iflen(args)==1

sok=args[0](string)

s=fmtSprint(args)

returnbeegoTranslationMoney(s)

Multi-languagedevelopment1 Settingthelanguageandlocationofthelanguagepacktheninitializei18nobjects

beegoLang=zh

beegoLangPath=viewslang

beegoInitLang()

2 Designingamulti-languagepackage

Abovewetalkedabouthowtoinitializeamulti-languagepackageNowletslookathowtodesignoneMulti-languagepackagesaretypicallyJSONfilesasyouvealreadyseeninChapter10WemustprovidetranslationfilesforlanguageswewishtosupportonourLangPathsuchasthefollowing

zhjson

submit提交

create创建

enjson

submitSubmit

createCreate

3 Usinglanguagepackages

Wecancallthecontrollertogetthetranslatedresponseinthedesiredlanguagelikeso

thisData[create]=beegoTranslationTranslate(create)

Wecanalsodirectlyinterpolatetranslatedresponsesinourtemplates

DirectTexttranslation

create|Trans

Timetotranslate

time|TransDate

Currencytranslation

money|TransMoney

LinksDirectoryPrevioussectionUservalidationNextsectionpprof

146pprofAgreatfeatureofGosstandardlibraryisitscodeperformancemonitoringtoolsThesepackagesexistintwoplaces

nethttppprof

runtimepprof

InfactnethttppprofsimplyexposesruntimeprofilingdatafromtheruntimepprofpackageonanHTTPport

pprofsupportinBeegoTheBeegoframeworkcurrentlysupportspprofhoweveritisnotturnedonbydefaultIfyouneedtotesttheperformanceofyourapplication(forinstancebyviewingtheexecutiongoroutine)suchinformationfromGosdefaultpackagenethttppprofalreadyhasthisfeatureBecausebeegohasrepackagedtheServHTTPfunctionyoucannotopenthedefaultfeatureincludedinpprofThisresultedinbeegosupportingpprofinternally

FirstinourbeegoRunfunctionwechoosewhetherornottoautomaticallyloadtheperformancepackaccordingtoourconfigurationvariable(inthiscasePprofOn)

ifPprofOn

BeeAppRegisterController(`debugpprof`ampProfController)

BeeAppRegisterController(`debugpprofpp([w]+)`ampProfController)

DesigningProfController

packagebeego

import(

nethttppprof

typeProfControllerstruct

Controller

func(thisProfController)Get()

switchthisCtxParams[pp]

default

pprofIndex(thisCtxResponseWriterthisCtxRequest)

casecmdline

pprofCmdline(thisCtxResponseWriterthisCtxRequest)

caseprofile

pprofProfile(thisCtxResponseWriterthisCtxRequest)

casesymbol

pprofSymbol(thisCtxResponseWriterthisCtxRequest)

thisCtxResponseWriterWriteHeader(200)

GettingstartedFromtheabovewecanseethatenablingpprofisassimpleassettingthePprofOnconfigurationvariabletotrue

beegoPprofOn=true

YoucanthenopenthefollowingURLinyourbrowsertoseethefollowinginterface

Figure147currentsystemgoroutineheapthreadinformation

Byclickingonagoroutinewecanseealotofdetailedinformation

Figure148showsthecurrentgoroutinedetails

Ofcoursewecanalsogetmoredetailsfromthecommandline

gotoolpprofhttplocalhost8080debugpprofprofile

Thistimetheprogramwillbeginprofilingtheapplicationforaperiodof30secondsduringwhichtimeitwillrepeatedlyrefreshthepageinthebrowserinanattempttogatherCPUusageandperformancedata

(pprof)top10

Total3samples

13333331333MHeap_AllocLocked

13336671333osexec(Cmd)closeDescriptors

133310001333runtimesigprocmask

00010001333MCentral_Grow

00010002667mainCompile

00010002667maincompile

00010002667mainrun

00010001333makeslice1

00010002667nethttp(ServeMux)ServeHTTP

00010002667nethttp(conn)serve

(pprof)web

Figure149showstheexecutionflowofinformation

LinksDirectoryPrevioussectionMulti-languagesupportNextsectionSummary

147SummaryThischapterillustratessomewaysinwhichtheBeegoframeworkcanbeextendedWefirstlookedatstaticfilesupportlearninghowBeegohandlesservingstaticfilesinternallyWesawhowthisfunctionalityallowedustoeasilyintegratestaticassets(suchasBootstrapsCSSfiles)forrapidandgreatlookingwebsitedevelopmentNextwesawhowtointegratesessionManagertopainlesslyfacilitateusersessionsinBeegoWethendescribedformmanagementandvalidationleveragingGosstructstoreducecoderepetitionandforsimplifyingfieldvalidationAfterthatwediscusseduserauthenticationwhichinvolvedthreemainstrategiesHTTPauthentication(basicanddigest)thirdpartyauthenticationandcustomauthenticationWelearnedaboutsomeexistingthirdpartyauthenticationpackagesthathavealreadyimplementedthesestrategieswhichareconvenientlyaccommodatedbyBeegoThenextsectionre-introducedlanguagesupportinBeegowesawhowtointegratethego-i18npackageandlearnedhowtoeasilyloadmultiplelanguagepacksintoourapplicationsasneededLastlywediscussedhowtoworkwithGospprofpackagesinBeegoThepprofpackageisusedforperformanceprofilinginGoandBeegorepackagesitsoitcanservethesamepurposeinBeegoapplicationswithoutmuchadditionalworkThroughthesesixsectionsweveextendedBeegowithmanyfeaturesmakingitintoaversatileframeworksuitablefortherequirementsofmanywebapplicationsUsershavethefreedomofextendingtheframeworktosuittheirindividualneedsthisbriefintroductiontoBeegosimplyoffersasmalltasteofwhatcanbedone

LinksDirectoryPrevioussectionpprofNextchapterAppendixAReferences

Summary

AppendixAReferencesThisbookisasummaryofmyGoexperiencesomecontentarefromotherGopherseitherblogsorsitesThankstothem

1 golangblog2 RussCoxsblog3 gobook4 golangtutorials5 轩脉刃de刀光剑影

6 GoProgrammingLanguage7 NetworkprogrammingwithGo8 setup-the-rails-application-for-internationalization9 TheCross-SiteScripting(XSS)FAQ

References

1Goenvironmentconfiguration11Installation12$GOPATHandworkspace13Gocommands14Godevelopmenttools15Summary

2Gobasicknowledge21HelloGo22Gofoundation23Controlstatementsandfunctions24struct25Object-oriented26interface27Concurrency28Summary

3Webfoundation31Webworkingprinciples32Buildasimplewebserver33HowGoworkswithweb34Getintohttppackage35Summary

4Userform41Processforminputs42Verificationofinputs43Crosssitescripting44Duplicatesubmissions45Fileupload46Summary

5Database51databasesqlinterface52MySQL53SQLite54PostgreSQL55DevelopORMbasedonbeedb56NoSQLdatabase57Summary

6Datastorageandsession61Sessionandcookies62HowtousesessioninGo63Sessionstorage64Preventhijackofsession65Summary

7Textfiles71XML72JSON73Regexp74Templates75Files76Strings77Summary

8Webservices81Sockets82WebSocket

preface

83REST84RPC85Summary

9Securityandencryption91CSRFattacks92Filterinputs93XSSattacks94SQLinjection95Passwordstorage96Encryptanddecryptdata97Summary

10Internationalizationandlocalization101Timezone102Localizedresources103Internationalsites104Summary

11Errorhandlingdebuggingandtesting111Errorhandling112DebuggingbyusingGDB113Writetestcases114Summary

12Deploymentandmaintenance121Logs122Errorsandcrashes123Deployment124Backupandrecovery125Summary

13Buildawebframework131Projectprogram132Customizedrouters133Designcontrollers134Logsandconfigurations135Adddeleteandupdateblogs136Summary

14Developwebframework141Staticfiles142Session143Form144Uservalidation145Multi-languagesupport146pprof147Summary

AppendixAReferences

preface

Introduction

Go Environment Configuration

Installation

$GOPATH and workspace

Go commands

Go development tools

Summary

Go basic knowledge

Hello Go

Go foundation

Control statements and functions

struct

Object-oriented

interface

Concurrency

Summary

Web foundation

Web working principles

Build a simple web server

How Go works with web

Get into http package

Summary

HTTP Form

Process form inputs

Validation of inputs

Cross site scripting

Duplicate submissions

File upload

Summary

Database

databasesql interface

How to use MySQL

How to use SQLite

How to use PostgreSQL

How to use beedb ORM

NOSQL

Summary

Data storage and session

Session and cookies

How to use session in Go

Session storage

Prevent hijack of session

Summary

Text files

XML

JSON

Regexp

Templates

Files

Strings

Summary

Web services

Sockets

WebSocket

REST

RPC

Summary

Security and encryption

CSRF attacks

Filter inputs

XSS attacks

SQL injection

Password storage

Encrypt and decrypt data

Summary

Internationalization and localization

Time zone

Localized resources

International sites

Summary

Error handling debugging and testing

Error handling

Debugging by using GDB

Write test cases

Summary

Deployment and maintenance

Logs

Errors and crashes

Deployment

Backup and recovery

Summary

Build a web framework

Project program

Customized routers

Design controllers

Logs and configurations

Add delete and update blogs

Summary

Develop web framework

Static files

Session

Form

User validation

Multi-language support

pprof

Summary

References

preface

HowtousesessioninGo

Sessionstorage

Summary

Textfiles

Regexp

Templates

Strings

Summary

Webservices

Sockets

WebSocket

Summary

CSRFattacks

Filterinputs

XSSattacks

SQLinjection

Passwordstorage

Summary

Timezone

Localizedresources

Internationalsites

Summary

Errorhandling

DebuggingbyusingGDB

Writetestcases

Summary

Errorsandcrashes

Deployment

Backupandrecovery

Summary

Buildawebframework

Projectprogram

Customizedrouters

Designcontrollers

Summary

Developwebframework

Staticfiles

Session

Uservalidation

Summary

References

preface

Donate

AliPay

alipay

EnglishDonatedonate

BBShttpgocnio

GetStarted

Introduction

11Installation

cdgosrc

allbash

Installation

x86_64GNULinux

Installation

Windows

Usethird-partytools

gvminstallgo183

gvmusego183

apt-get

sudoapt-getupdate

Goenvironment

1 InstallHomebrew

Installation

1 InstallGo

brewinstallgo

Installation

cd$GOPATHsrc

mkdirmymath

$GOPATHandworkspace

packagemymath

fori=0ilt1000i++

z-=(zz-x)(2x)

returnz

mymatha

cd$GOPATHsrc

mkdirmathapp

cdmathapp

vimmaingo

packagemain

import(

mymath

funcmain()

$GOPATHandworkspace

$GOPATH

|-githubcom

|-astaxie

|-beedb

|--$GOOS_$GOARCH

|-githubcom

|-astaxie

|-beedba

mathapp

mymatha

githubcom

astaxie

beedba

mathapp

maingo

mymath

sqrtgo

githubcom

astaxie

beedbgo

utilgo

$GOPATHandworkspace

13Gocommands

Gocommands

Github(git)

Launchpad(Bazaar)

okarchivetar0011s

FAILarchivezip0022s

okcompressgzip0033s

Gocommands

LiteIDEfeatures

Downloadpage

Godevelopmenttools

Sourcecode

Installgocode

GOROOT=cgo

GOBIN=

GOARCH=amd64

GOOS=windows

CGO_ENABLED=1

GOROOT=$HOMEgo

GOBIN=

GOARCH=amd64

GOOS=linux

CGO_ENABLED=1

Godevelopmenttools

Syntaxhighlight

erencesmenu

Godevelopmenttools

1InstallVundle

mkdir~vimbundle

filetypeoffrequired

callvundlebegin()

2InstallVim-go

Pluginfatihvim-go

syntaxon

3 Installgocode

Godevelopmenttools

4 Configuregocode

~updatesh

~gocodeset

2 Installgocode

3 Configuregocode

~updatebash

~gocodeset

Configure~emacsfile

Godevelopmenttools

auto-complete

(ac-config-default)

5 Configureemacs

golangmode

speedbar

(speedbar1)

(add-hook

go-mode-hook

(lambda()

gocode

ImenuampSpeedbar

(func^func()1)))

Outlinemode

Menubar

(requireeasymenu)

(Gotools

[Gorunbuffergot]

(easy-menu-define

go-added-menu

(current-local-map)

Gotools

go-hooked-menu)

helperfunction

(defungo()

runcurrentbuffer

(interactive)

helperfunction

(interactive)

(ifbuffer-read-only

(progn

(ding)

(show-all)

Godevelopmenttools

(progn

matErrorst))

(progn

(erase-buffer)

(progn

helperfunction

(interactive)

(show-all)

gocodeinGithub

Godevelopmenttools

Figure114gdbSetting

Godevelopmenttools

Downloadhttpsatomio

Godevelopmenttools

Summary

Gobasicknowledge

HelloGo

AreyoureadyLetsGo

packagemain

importfmt

funcmain()

HelloGo

funcmain()

HelloGo

varvariableNametype

Gofoundation

_b=3435

packagemain

funcmain()

variint

Moreexamples

constPi=31415926

consti=10000

constMaxThread=10

Elementarytypes

Boolean

samplecode

functest()

Numericaltypes

Gofoundation

varaint8

varbint32

varccomplex64=5+5i

output(5+5i)

String

samplecode

functest()

varsstring=hello

s[0]=c

s=hello

c[0]=c

fmtPrintf(sns2)

s=hello

m=world

fmtPrintf(sna)

andalso

Gofoundation

s=hello

fmtPrintf(sns)

m=`hello

world`

iferr=nil

fmtPrint(err)

Someskills

Definebygroup

Basicform

importfmt

importos

consti=100

constpi=31415

constprefix=Go_

variint

varpifloat32

varprefixstring

Groupform

Gofoundation

import(

const(

pi=31415

prefix=Go_

pifloat32

prefixstring

iotaenumerate

const(

x=iotax==0

y=iotay==1

z=iotaz==2

const(

Somerules

arrayslicemap

vararr[n]type

Gofoundation

b=[10]int123

varfslice[]int

slice=[]byteabcd

Gofoundation

varab[]byte

a=ar[25]

b=ar[35]

defineanarray

definetwoslices

slicefromslice

Slice_a=Array_a[25]

Gofoundation

numbers[ten]=10

numbers[three]=3

Initializeamap

Gofoundation

m[Hello]=Bonjour

newreturnspointers

int320

int640

uint0x0

boolfalse

string

Gofoundation

ifxgt10

fmtPrintln(x)

ifinteger==3

elseifintegerlt3

funcmyFunc()

Herelabelendswith

fmtPrintln(i)

packagemain

importfmt

funcmain()

sum+=index

Printsumisequalto45

forsumlt1000

sum+=sum

forsumlt1000

sum+=sum

ifindex==5

breakorcontinue

fmtPrintln(index)

breakprints109876

forkv=rangemap

for_v=rangemap

yourlogic

switchsExpr

caseexpr1

someinstructions

caseexpr2

caseexpr3

default

othercode

switchi

case234

case10

default

integer=6

switchinteger

fallthrough

default

integerlt=6

integerlt=7

integerlt=8

defaultcase

functionbody

multi-valuereturn

returnvalue1value2

packagemain

importfmt

funcmax(abint)int

ifagtb

returna

returnb

funcmain()

Multi-valuereturn

packagemain

importfmt

returnA+BAB

funcmain()

add=A+B

multiplied=AB

return

Variadicfunctions

funcmyfunc(argint)

for_n=rangearg

packagemain

importfmt

funcadd1(aint)int

funcmain()

packagemain

importfmt

funcadd1(aint)int

funcmain()

funcReadWrite()bool

fileOpen(file)

Dosomework

iffailureX

fileClose()

returnfalse

iffailureY

fileClose()

returnfalse

fileClose()

returntrue

funcReadWrite()bool

fileOpen(file)

deferfileClose()

iffailureX

returnfalse

iffailureY

returnfalse

returntrue

fori=0ilt5i++

deferfmtPrintf(di)

packagemain

importfmt

returninteger2=0

returninteger2==0

varresult[]int

iff(value)

returnresult

funcmain()

PanicandRecover

funcinit()

ifuser==

deferfunc()

ifx=recover()x=nil

b=true

return

import

import(

databasesql

24struct

typepersonstruct

namestring

ageint

Therearetwofields

Letsseehowtouseit

typepersonstruct

namestring

ageint

P=personTom25

struct

packagemain

importfmt

defineanewtype

typepersonstruct

namestring

ageint

ifp1agegtp2age

returnp1p1age-p2age

returnp2p2age-p1age

funcmain()

vartomperson

tomnametomage=Tom18

paul=personPaul43

Letsseeoneexample

struct

packagemain

importfmt

typeHumanstruct

namestring

ageint

weightint

typeStudentstruct

specialtystring

funcmain()

accessfields

markspecialty=AI

markage=46

markweight+=60

markHumanage-=1

struct

packagemain

importfmt

typeSkills[]string

typeHumanstruct

namestring

ageint

weightint

typeStudentstruct

specialtystring

funcmain()

accessfields

modifyembeddedfield

janeint=3

struct

packagemain

importfmt

typeHumanstruct

namestring

ageint

typeEmployeestruct

specialtystring

funcmain()

struct

packagemain

importfmt

typeRectanglestruct

widthheightfloat64

returnrwidthrheight

funcmain()

r1=Rectangle122

r2=Rectangle94

AsRobPikesaid

Syntaxofmethod

Object-oriented

packagemain

import(

typeCirclestruct

radiusfloat64

typeRectanglestruct

widthheightfloat64

method

returnrwidthrheight

funcmain()

c1=Circle10

c2=Circle25

r1=Rectangle94

r2=Rectangle122

Object-oriented

typeageint

typemoneyfloat32

m=months

January31

February28

December31

packagemain

importfmt

const(

WHITE=iota

YELLOW

typeBoxstruct

colorColor

typeColorbyte

method

bcolor=c

method

k=Color(WHITE)

for_b=rangebl

ifbVolume()gtv

v=bVolume()

k=bcolor

returnk

method

fori_=rangebl

method

Object-oriented

returnstrings[c]

funcmain()

boxes=BoxList

Box444RED

Box10101YELLOW

Box1120BLACK

Box10101BLUE

Box10301WHITE

Box202020YELLOW

boxesPaintItBlack()

Inheritanceofmethod

Object-oriented

packagemain

importfmt

typeHumanstruct

namestring

ageint

phonestring

typeStudentstruct

Humananonymousfield

schoolstring

typeEmployeestruct

companystring

func(hHuman)SayHi()

funcmain()

samSayHi()

markSayHi()

Object-oriented

packagemain

importfmt

typeHumanstruct

namestring

ageint

phonestring

typeStudentstruct

schoolstring

typeEmployeestruct

companystring

func(hHuman)SayHi()

funcmain()

samSayHi()

markSayHi()

Object-oriented

26Interface

Whatisaninterface

interface

typeHumanstruct

namestring

ageint

phonestring

typeStudentstruct

schoolstring

loanfloat32

typeEmployeestruct

companystring

moneyfloat32

defineinterfaces

typeMeninterface

SayHi()

Sing(lyricsstring)

SayHi()

Sing(songstring)

SayHi()

Sing(songstring)

func(hHuman)SayHi()

Valueofinterface

interface

packagemain

importfmt

typeHumanstruct

namestring

ageint

phonestring

typeStudentstruct

schoolstring

loanfloat32

typeEmployeestruct

companystring

moneyfloat32

typeMeninterface

SayHi()

Sing(lyricsstring)

method

func(hHuman)SayHi()

method

funcmain()

defineinterfacei

variMen

icanstoreStudent

i=mike

iSayHi()

iSing(Novemberrain)

icanstoreEmployee

iSayHi()

interface

iSing(Borntobewild)

sliceofMen

x=make([]Men3)

for_value=rangex

valueSayHi()

Emptyinterface

varvoidinterface

s=Helloworld

void=i

void=s

String()string

interface

packagemain

import(

strconv

typeHumanstruct

namestring

ageint

phonestring

funcmain()

interface

packagemain

import(

strconv

typeList[]Element

typePersonstruct

namestring

ageint

funcmain()

list=make(List3)

list[0]=1anint

switchtest

interface

packagemain

import(

strconv

typeList[]Element

typePersonstruct

namestring

ageint

funcmain()

list=make(List3)

list[0]=1anint

caseint

casestring

casePerson

default

Embeddedinterfaces

interface

Len()int

Less(ijint)bool

Swap(ijint)

ioReadWriter

Reader

Writer

Reflection

varxfloat64=34

t=reflectTypeOf(x)

v=reflectValueOf(x)

fmtPrintln(typet)

fmtPrintln(valuev)

varxfloat64=34

v=reflectValueOf(x)

vSetFloat(71)

varxfloat64=34

v=pElem()

vSetFloat(71)

interface

gohello(abc)

Letsseeanexample

packagemain

import(

runtime

funcsay(sstring)

fori=0ilt5i++

runtimeGosched()

fmtPrintln(s)

funcmain()

Output

Concurrency

ci=make(chanint)

cs=make(chanstring)

Letsseemoreexamples

packagemain

importfmt

total=0

for_v=rangea

total+=v

funcmain()

a=[]int728-940

c=make(chanint)

gosum(a[len(a)2]c)

fmtPrintln(xyx+y)

Concurrency

ch=make(chantypen)

packagemain

importfmt

funcmain()

fmtPrintln(lt-c)

packagemain

import(

fori=0iltni++

xy=yx+y

close(c)

funcmain()

c=make(chanint10)

fori=rangec

fmtPrintln(i)

Concurrency

packagemain

importfmt

select

caseclt-x

xy=yx+y

caselt-quit

fmtPrintln(quit)

return

funcmain()

c=make(chanint)

quit=make(chanint)

gofunc()

fori=0ilt10i++

fmtPrintln(lt-c)

quitlt-0

fibonacci(cquit)

select

casei=lt-c

default

funcmain()

c=make(chanint)

o=make(chanbool)

gofunc()

select

casev=lt-c

println(v)

println(timeout)

olt-true

Concurrency

runtimeGoexit()

runtimeGosched()

runtimeNumCPU()int

Concurrency

Summary

Webfoundation

pathresourcespath

anchoranchor

browserinformation

blankline

-1xxInformational

-2xxSuccess

-3xxRedirection

-4xxClientError

-5xxServerError

Requestinstance

packagemain

import(

nethttp

strings

forkv=rangerForm

fmtPrintln(keyk)

funcmain()

iferr=nil

HowGoworkswithweb

Buildversiongo112

deferlClose()

rwe=lAccept()

ife=nil

iftempDelay==0

tempDelay=2

tempDelay=max

continue

returne

tempDelay=0

cerr=srvnewConn(rw)

iferr=nil

continue

gocserve()

Detailedworkflow

HowGoworkswithweb

cerr=srvnewConn(rw)

iferr=nil

continue

gocserve()

typeServeMuxstruct

ThestructofmuxEntry

typemuxEntrystruct

hHandler

Getintohttppackage

ServeHTTPcallsf(wr)

muxmuRLock()

defermuxmuRUnlock()

ifh==nil

h=NotFoundHandler()

returnh

packagemain

import(

nethttp

typeMyMuxstruct

ifrURLPath==

sayhelloName(wr)

return

httpNotFound(wr)

return

funcmain()

mux=ampMyMux

Getintohttppackage

samplecode

TODOaddhttp404error

ifrMethod==GET

ifmessage=

message=

ifrMethod==DELETE

ifid==all

dbDeleteAll()

iferr=nil

fmtPrintln(err)

iferr=nil

message=Taskdeleted

Getintohttppackage

Summary

ltformgt

inputelements

ltformgt

HTTPForm

lthtmlgt

ltheadgt

lttitlegtlttitlegt

ltheadgt

ltbodygt

ltformgt

ltbodygt

lthtmlgt

Processforminputs

packagemain

import(

htmltemplate

nethttp

strings

forkv=rangerForm

fmtPrintln(keyk)

ifrMethod==GET

tExecute(wnil)

rParseForm()

logicpartoflogin

funcmain()

iferr=nil

Processforminputs

v=urlValues

vSet(nameAva)

vAdd(friendJess)

vAdd(friendSarah)

vAdd(friendZoe)

Processforminputs

codeforemptyfield

iferr=nil

checkrangeofnumber

ifgetintgt100

toobig

returnfalse

Chinese

Validationofinputs

returnfalse

fmtPrintln(no)

fmtPrintln(yes)

ltselectgt

for_v=rangeslice

returntrue

returnfalse

Radiobuttons

Validationofinputs

slice=[]int12

for_v=rangeslice

returntrue

returnfalse

ifa==nil

returntrue

returnfalse

LinksDirectory

Validationofinputs

importtexttemplate

Output

importhtmltemplate

Output

Crosssitescripting

importhtmltemplate

Output

Crosssitescripting

ifrMethod==GET

h=md5New()

tExecute(wtoken)

loginrequest

rParseForm()

iftoken=

checktokenvalidity

giveerrorifnotoken

lthtmlgt

ltheadgt

ltbodygt

ltformgt

ltbodygt

lthtmlgt

uploadlogic

ifrMethod==GET

h=md5New()

tExecute(wtoken)

iferr=nil

fmtPrintln(err)

return

deferfileClose()

iferr=nil

fmtPrintln(err)

return

deferfClose()

ioCopy(ffile)

Fileupload

Filenamestring

Fileupload

packagemain

import(

ioioutil

mimemultipart

nethttp

iferr=nil

returnerr

openfilehandle

iferr=nil

returnerr

deferfhClose()

iocopy

iferr=nil

returnerr

bodyWriterClose()

iferr=nil

returnerr

iferr=nil

returnerr

returnnil

sampleusage

funcmain()

filename=astaxiepdf

Fileupload

Summary

Database

funcinit()

import(

databasesql

typeDriverinterface

typeConninterface

Close()error

Begin()(Txerror)

typeStmtinterface

Close()error

NumInput()int

driverTx

typeTxinterface

Commit()error

Rollback()error

typeExecerinterface

typeResultinterface

typeRowsinterface

Columns()[]string

Close()error

typeValueinterface

float64

[]byte

timeTime

typeValuerinterface

Value()(Valueerror)

typeDBstruct

driverdriverDriver

dsnstring

closedbool

PRIMARYKEY(`uid`)

packagemain

import(

databasesql

funcmain()

checkErr(err)

insert

checkErr(err)

fmtPrintln(id)

update

HowtouseMySQL

checkErr(err)

fmtPrintln(affect)

checkErr(err)

forrowsNext()

varuidint

varusernamestring

vardepartmentstring

varcreatedstring

checkErr(err)

fmtPrintln(uid)

fmtPrintln(created)

delete

checkErr(err)

reserr=stmtExec(id)

checkErr(err)

fmtPrintln(affect)

dbClose()

iferr=nil

panic(err)

userpassworddbname

HowtouseMySQL

`created`DATENULL

Anexample

packagemain

import(

databasesql

funcmain()

checkErr(err)

insert

checkErr(err)

fmtPrintln(id)

update

checkErr(err)

HowtouseSQLite

checkErr(err)

fmtPrintln(affect)

checkErr(err)

varuidint

varusernamestring

vardepartmentstring

varcreatedtimeTime

forrowsNext()

checkErr(err)

fmtPrintln(uid)

fmtPrintln(created)

delete

checkErr(err)

reserr=stmtExec(id)

checkErr(err)

fmtPrintln(affect)

dbClose()

iferr=nil

panic(err)

ifrowsNext()

checkErr(err)

fmtPrintln(uid)

fmtPrintln(created)

Transactions

HowtouseSQLite

iferr=nil

fmtPrintln(err)

iferr=nil

fmtPrintln(err)

iferr=nil

txRollback()

txCommit()

HowtouseSQLite

CREATETABLEuserinfo

uidserialNOTNULL

Createddate

WITH(OIDS=FALSE)

Anexample

packagemain

import(

databasesql

_githubcomlibpq

const(

DB_USER=postgres

DB_NAME=test

funcmain()

checkErr(err)

deferdbClose()

varlastInsertIdint

HowtousePostgreSQL

checkErr(err)

forrowsNext()

varuidint

varusernamestring

vardepartmentstring

varcreatedtimeTime

checkErr(err)

iferr=nil

panic(err)

HowtousePostgreSQL

import(

databasesql

iferr=nil

panic(err)

orm=beedbNew(db)

HowtousebeedbORM

PostgreSQL

orm=beedbNew(dbpg)

beedbOnDebug=true

typeUserinfostruct

Usernamestring

Departnamestring

CreatedtimeTime

varsaveoneUserinfo

ormSave(ampsaveone)

Insertmultipledata

HowtousebeedbORM

t[username]=astaxie

varuserUserinfo

Example2

varuser2Userinfo

varuser3Userinfo

varuser4Userinfo

HowtousebeedbORM

typeProfilestruct

Nicknamestring

Mobilestring

typeUserinfostruct

Uidint

PK_Usernamestring

Departnamestring

CreatedtimeTime

ProfileHasOne

HowtousebeedbORM

packagemain

import(

ossignal

syscall

PoolredisPool

funcinit()

redisHost=6379

close()

returnampredisPool

MaxIdle3

iferr=nil

returnnilerr

returncerr

_err=cDo(PING)

returnerr

funcclose()

gofunc()

PoolClose()

osExit(0)

conn=PoolGet()

deferconnClose()

vardata[]byte

iferr=nil

returndataerr

funcmain()

testerr=Get(test)

fmtPrintln(testerr)

packagemain

import(

funcmain()

stringmanipulation

val_=clientGet(a)

clientDel(a)

listoperation

vals=[]stringabcde

for_v=rangevals

foriv=rangedbvals

println(istring(v))

clientDel(l)

Installmgo

gogetgopkginmgov2

Hereistheexample

packagemain

import(

gopkginmgov2

gopkginmgov2bson

typePersonstruct

Namestring

Phonestring

funcmain()

iferr=nil

panic(err)

defersessionClose()

iferr=nil

logFatal(err)

result=Person

iferr=nil

logFatal(err)

Summary

Sessionandcookies

typeCookiestruct

Namestring

Valuestring

Pathstring

Domainstring

ExpirestimeTime

RawExpiresstring

MaxAgeint

Securebool

HttpOnlybool

Rawstring

fmtFprint(wcookie)

Sessionandcookies

Sessionmanager

HowtousesessioninGo

typeManagerstruct

providerProvider

maxlifetimeint64

funcinit()

HowtousesessioninGo

itpanics

ifprovider==nil

b=make([]byte32)

return

managerlockLock()

return

rParseForm()

ifrMethod==GET

httpRedirect(wr302)

HowtousesessioninGo

ifcreatetime==nil

ifct==nil

sessSet(countnum1)

Destroysessionid

return

managerlockLock()

Deletesessions

HowtousesessioninGo

funcinit()

managerlockLock()

HowtousesessioninGo

packagememory

import(

containerlist

stvalue[key]=value

returnnil

returnv

returnnil

delete(stvaluekey)

returnnil

returnstsid

typeProviderstruct

locksyncMutexlock

listlistListgc

pderlockLock()

returnnewsessnil

Sessionstorage

returnsesserr

returnnilnil

returnnil

pderlockLock()

ifelement==nil

pderlockLock()

returnnil

funcinit()

import(

Sessionstorage

funcinit()

Sessionstorage

ifct==nil

sessSet(countnum1)

HiNowcount

cookieonlyandtoken

h=md5New()

asktologin

sessSet(tokentoken)

ifcreatetime==nil

Summary

Textfiles

ltservergt

ltserversgt

Samplecode

packagemain

import(

encodingxml

ioioutil

typeserverstruct

funcmain()

iferr=nil

return

deferfileClose()

iferr=nil

return

v=Recurlyservers

iferr=nil

return

fmtPrintln(v)

ltservergt

packagemain

import(

encodingxml

typeServersstruct

typeserverstruct

funcmain()

iferr=nil

ltservergt

ltserversgt

ParseJSON

Parsetostruct

packagemain

import(

encodingjson

typeServerstruct

ServerNamestring

ServerIPstring

Servers[]Server

funcmain()

varsServerslice

127002]`

fmtPrintln(s)

varfinterface

NameWednesday

Parents[]interface

Morticia

forkv=rangem

switchvv=v(type)

casestring

caseint

casefloat64

case[]interface

foriu=rangevv

fmtPrintln(iu)

default

array[123]

float5150

bignum9223372036854775807

stringsimplejson

booltrue

packagemain

import(

encodingjson

typeServerstruct

ServerNamestring

ServerIPstring

Servers[]Server

funcmain()

varsServerslice

berr=jsonMarshal(s)

iferr=nil

Output

typeServerstruct

Example

typeServerstruct

IDwillnotbeoutputed

IDint`json-`

s=Server

ServerName`Go10`

ServerName2`Go10`

ServerIP``

b_=jsonMarshal(s)

osStdoutWrite(b)

Output

returnfalse

returntrue

funcmain()

iflen(osArgs)==1

osExit(1)

fmtPrintln(Number)

Regexp

packagemain

import(

ioioutil

nethttp

regexp

strings

funcmain()

iferr=nil

return

src=string(body)

RemoveSTYLE

RemoveSCRIPT

Regexp

Codesample

Regexp

packagemain

import(

regexp

funcmain()

Findthefirstmatch

sgreaterthan0

Output

thethirdelementuage

for_v=rangesubmatch

SameasFindIndex()

Regexp

SohowdoweuseExpand

funcmain()

src=[]byte(`

callhelloalice

hellobob

callhelloeve

res=[]byte

Regexp

74Templates

Example

Fields

Templates

packagemain

import(

htmltemplate

typePersonstruct

UserNamestring

funcmain()

tExecute(osStdoutp)

typePersonstruct

UserNamestring

Nestedfields

Moreexamples

Templates

packagemain

import(

htmltemplate

typeFriendstruct

Fnamestring

typePersonstruct

UserNamestring

Emails[]string

Friends[]Friend

funcmain()

rangeEmails

anemail

withFriends

myfriendnameisFname

tExecute(osStdoutp)

packagemain

import(

texttemplate

funcmain()

Templates

pipelines

$variable=pipeline

Moreexamples

Templatefunctions

Example

Templates

packagemain

import(

htmltemplate

strings

typeFriendstruct

Fnamestring

typePersonstruct

UserNamestring

Emails[]string

Friends[]Friend

ok=false

varsstring

iflen(args)==1

sok=args[0](string)

s=fmtSprint(args)

findthesymbol

iflen(substrs)=2

returns

replacethebyat

funcmain()

rangeEmails

anemails|emailDeal

withFriends

myfriendnameisFname

tExecute(osStdoutp)

Templates

varbuiltins=FuncMap

andand

callcall

htmlHTMLEscaper

indexindex

jsJSEscaper

lenlength

notnot

printfmtSprint

printffmtSprintf

printlnfmtSprintln

packagemain

import(

texttemplate

funcmain()

Output

ThefirstoneparsedOK

Templates

Maintemplate

headertmpl

defineheader

lthtmlgt

ltheadgt

ltbodygt

contenttmpl

definecontent

templateheader

ltulgt

templatefooter

footertmpl

definefooter

ltbodygt

lthtmlgt

endraw

Templates

packagemain

import(

ioioutil

texttemplate

funcmain()

varallFiles[]string

iferr=nil

fmtPrintln(err)

for_file=rangefiles

filename=fileName()

fmtPrintln()

lttitlegt

Templates

typeTaskstruct

Titlestring

Contentstring

Createdstring

typeContextstruct

Tasks[]Task

Navigationstring

Searchstring

Messagestring

vartask[]typesTask

rangeTasks

Content

Templates

ifTasksrangeTasks

ltdivclass=notegt

lthrgt

ltulgt

ltspangt

ltdivgt

endelse

ltdivclass=notegt

ltdivgt

Templates

Codesample

packagemain

import(

funcmain()

iferr=nil

fmtPrintln(err)

Createandopenfiles

Writeastringtoafile

Codesample

packagemain

import(

funcmain()

userFile=astaxietxt

iferr=nil

return

deferfoutClose()

fori=0ilt10i++

Readdatatob

Codesample

packagemain

import(

funcmain()

userFile=asatxietxt

iferr=nil

return

deferflClose()

n_=flRead(buf)

if0==n

s=[]stringfoobarbaz

Outputfoobarbaz

Output4

Outputbanana

moomoomoo

Strings

Output[abc]

Output[Achtung]

import(fmtstrconv)

packagemain

import(

strconv

funcmain()

e=strconvItoa(1023)

fmtPrintln(abcde)

import(fmtstrconv)

Strings

Summary

Webservices

Sockets

IPtypesinGo

typeIP[]byte

packagemain

import(

funcmain()

iflen(osArgs)=2

osExit(1)

name=osArgs[1]

ifaddr==nil

osExit(0)

Sockets

typeTCPAddrstruct

Portint

HEADHTTP10rnrn

HTTP10200OK

ETag-9985996

Content-Length18074

Connectionclose

Serverlighttpd1423

Clientcode

Sockets

packagemain

import(

ioioutil

funcmain()

iflen(osArgs)=2

osExit(1)

service=osArgs[1]

checkError(err)

osExit(0)

iferr=nil

osExit(1)

TCPserver

Sockets

packagemain

import(

funcmain()

service=7777

checkError(err)

iferr=nil

continue

iferr=nil

osExit(1)

Sockets

packagemain

import(

funcmain()

service=1200

checkError(err)

iferr=nil

continue

deferconnClose()

iferr=nil

osExit(1)

Sockets

packagemain

import(

strconv

funcmain()

service=1200

checkError(err)

iferr=nil

continue

iferr=nil

fmtPrintln(err)

ifread_len==0

iferr=nil

osExit(1)

Sockets

UDPclientcodesample

packagemain

import(

funcmain()

iflen(osArgs)=2

osExit(1)

service=osArgs[1]

checkError(err)

varbuf[512]byte

checkError(err)

osExit(0)

iferr=nil

osExit(1)

Sockets

UDPservercodesample

packagemain

import(

funcmain()

service=1200

checkError(err)

handleClient(conn)

varbuf[512]byte

iferr=nil

return

iferr=nil

osExit(1)

Sockets

WebSocket

Clientcode

lthtmlgt

ltheadgtltheadgt

ltbodygt

varsock=null

consolelog(onload)

functionsend()

socksend(msg)

ltscriptgt

ltformgt

ltbodygt

lthtmlgt

WebSocket

Servercode

packagemain

import(

nethttp

varerrerror

varreplystring

msg=Received+reply

funcmain()

WebSocket

Resources

nlayer

Representation

StateTransfer

Tosummarizetheabove

Figure87RESTslevel

packagemain

import(

nethttp

uid=psByName(uid)

uid=rFormValue(uid)

uid=psByName(uid)

funcmain()

routerGET(Index)

RPCworkingprinciple

Forexample

packagemain

import(

errors

nethttp

netrpc

typeArgsstruct

typeQuotientstruct

QuoRemint

typeArithint

reply=argsAargsB

returnnil

ifargsB==0

quoQuo=argsAargsB

quoRem=argsAargsB

returnnil

funcmain()

arith=new(Arith)

rpcRegister(arith)

rpcHandleHTTP()

iferr=nil

Clientsidecode

packagemain

import(

netrpc

typeArgsstruct

typeQuotientstruct

QuoRemint

funcmain()

iflen(osArgs)=2

osExit(1)

iferr=nil

Synchronouscall

args=Args178

varreplyint

iferr=nil

varquotQuotient

iferr=nil

$http_clocalhost

Arith178=136

packagemain

import(

errors

netrpc

typeArgsstruct

typeQuotientstruct

QuoRemint

typeArithint

reply=argsAargsB

returnnil

ifargsB==0

quoQuo=argsAargsB

quoRem=argsAargsB

returnnil

funcmain()

arith=new(Arith)

rpcRegister(arith)

checkError(err)

iferr=nil

continue

rpcServeConn(conn)

iferr=nil

osExit(1)

Theclientsidecode

packagemain

import(

netrpc

typeArgsstruct

typeQuotientstruct

QuoRemint

funcmain()

iflen(osArgs)=2

osExit(1)

service=osArgs[1]

iferr=nil

Synchronouscall

args=Args178

varreplyint

iferr=nil

varquotQuotient

iferr=nil

JSONRPC

packagemain

import(

errors

netrpc

netrpcjsonrpc

typeArgsstruct

typeQuotientstruct

QuoRemint

typeArithint

reply=argsAargsB

returnnil

ifargsB==0

quoQuo=argsAargsB

quoRem=argsAargsB

returnnil

funcmain()

arith=new(Arith)

rpcRegister(arith)

checkError(err)

iferr=nil

continue

iferr=nil

osExit(1)

Theclientsidecode

packagemain

import(

netrpcjsonrpc

typeArgsstruct

typeQuotientstruct

QuoRemint

funcmain()

iflen(osArgs)=2

logFatal(1)

service=osArgs[1]

iferr=nil

Synchronouscall

args=Args178

varreplyint

iferr=nil

varquotQuotient

iferr=nil

Summary

91CSRFattacks

CSRFattacks

h=md5New()

tExecute(wtoken)

Outputtoken

Authenticationtoken

rParseForm()

iftoken=

Summary

CSRFattacks

secure

Filterinputs

WhoamI

ltselectname=namegt

ltselectgt

ltformgt

rParseForm()

name=rFormGet(name)

CleanMap[name]=name

rParseForm()

Filterinputs

XSSattacks

helloastaxie

http127001

XSSattacks

94SQLinjection

ltformgt

myuserorfoo=foo--

DbExec(sql)

SQLinjection

importcryptosha256

h=sha256New()

importcryptosha1

h=sha1New()

importcryptomd5

h=md5New()

Passwordstorage

packagemain

import(

funcmain()

iferr=nil

logFatal(err)

LinksDirectory

Passwordstorage

packagemain

import(

cryptoaes

cryptocipher

cryptorand

errors

funcmain()

iferr=nil

logFatal(err)

iferr=nil

logFatal(err)

iferr=nil

returnnilerr

iferr=nil

returnnilerr

iferr=nil

returnnilerr

iferr=nil

returnnilerr

typeBlockinterface

BlockSize()int

Summary

Fromthedomainname

ifrHost==wwwastacom

i18nSetLocale(en)

Timezone

ifprefix[0]==en

i18nSetLocale(en)

elseifprefix[0]==cn

elseifprefix[0]==tw

FromURLparameters

Accept-Language

ifAL==en

i18nSetLocale(en)

elseifAL==zh-CN

elseifAL==zh-TW

Timezone

IPAddress

Userprofile

Timezone

packagemain

importfmt

funcmain()

en[pea]=pea

en[bean]=bean

locales[en]=en

cn[pea]=豌豆

cn[bean]=毛豆

locales[zh-CN]=cn

lang=zh-CN

ifv2ok=v[key]ok

returnv2

return

Localizedresources

t=timeNow()

t=tIn(loc)

hourminsec=tClock()

Yreplacedby2012

mreplacedby10

dreplacedby24

en[money]=USDd

cn[money]=￥d元

Localizedresources

|--jsJSfiles

|--cssCSSfiles

indextplUserHome

logintplLogHome

|--images

|--css

indextpl

logintpl

VVLang=lang

jsfile

cssfile

Picturefiles

Localizedresources

zhjson

submit提交

create创建

enjson

submitSubmit

createCreate

Tr=i18nNewLocale()

Outputsubmit

TrSetLocale(zn)

Outputs递交

Internationalsites

iferr=nil

returnerr

deferdirClose()

iferr=nil

returnerr

for_name=rangenames

iferr=nil

returnerr

iffiIsDir()

returnerr

iferr=nil

returnerr

deferfileClose()

returnerr

returnnil

Outputyen1111

1textinformation

Internationalsites

ok=false

varsstring

iflen(args)==1

sok=args[0](string)

s=fmtSprint(args)

VSubmit|T

1 Thedateandtime

ok=false

varsstring

iflen(args)==1

sok=args[0](string)

s=fmtSprint(args)

returnTrTime(s)

VNow|TD

Internationalsites

ok=false

varsstring

iflen(args)==1

sok=args[0](string)

s=fmtSprint(args)

returnTrMoney(s)

VMoney|M

Internationalsites

Summary

iferr=nil

logFatal(err)

typeerrorinterface

Error()string

sstring

returnes

Errorhandling

ifflt0

implementation

ferr=Sqrt(-1)

iferr=nil

fmtPrintln(err)

returnerr

ifanerrorcondition

err=ampSyntaxError

Errorhandling

packagenet

typeErrorinterface

timeSleep(1e9)

continue

iferr=nil

logFatal(err)

funcinit()

record=new(Record)

return

iferr=fn(wr)err=nil

Errorhandling

funcinit()

record=new(Record)

returnerr

typeappErrorstruct

Errorerror

Messagestring

Codeint

cErrorf(veError)

record=new(Record)

returnnil

Summary

Errorhandling

11clt-i

13close(c)

16funcmain()

17msg=Startingmain

18fmtPrintln(msg)

19bus=make(chanint)

delete

DebuggingbyusingGDB

backtrace

30x0000000000000000in()

infolocals

infobreakpoints

infogoroutines

whatis

type=structstring

continue

setvariable

DebuggingbyusingGDB

packagemain

import(

fori=0ilt10i++

close(c)

funcmain()

msg=Startingmain

fmtPrintln(msg)

bus=make(chanint)

msg=startingagofunc

gocounting(bus)

forcount=rangebus

gdbgdbfile

(gdb)run

Startingmain

count0

count1

count2

count3

count4

count5

count6

count7

count8

count9

[LWP2771exited]

DebuggingbyusingGDB

(gdb)b23

(gdb)run

Startingmain

[NewLWP3284]

(gdb)list

18fmtPrintln(msg)

19bus=make(chanint)

21gocounting(bus)

22forcount=rangebus

(gdb)infolocals

count=0

bus=0xf840001a50

(gdb)pcount

(gdb)pbus

(gdb)whatisbus

type=chanint

(gdb)c

Continuing

count0

[NewLWP3303]

(gdb)c

Continuing

count1

DebuggingbyusingGDB

(gdb)infolocals

count=2

bus=0xf840001a50

(gdb)infolocals

count=9

bus=0xf840001a50

(gdb)c

Continuing

count9

(gdb)infogoroutines

(gdb)goroutine1bt

60x0000000000000000in()

DebuggingbyusingGDB

packagegotest

import(

errors

ifb==0

returnabnil

Hereisourtestcode

Writetestcases

packagegotest

import(

testing

exitstatus1

FAILgotest0013s

exitstatus1

FAILgotest0012s

Writetestcases

okgotest0013s

packagegotest

import(

testing

Division(45)

fori=0iltbNi++

Division(45)

okgotest9364s

Writetestcases

Summary

Firstinstallseelog

packagemain

funcmain()

deferlogFlush()

packagelogs

import(

errors

funcloadAppConfig()

appConfig=`

ltsmtpgt

ltfiltergt

ltoutputsgt

ltformatsgt

bySeeloggt

ltformatsgt

ltseeloggt

iferr=nil

fmtPrintln(err)

return

UseLogger(logger)

funcinit()

DisableLog()

loadAppConfig()

funcDisableLog()

Logger=newLogger

DisableLog

LoadAppConfig

Seelog

Outputs

Formats

UseLogger

packagemain

import(

nethttp

projectlogs

projectconfigs

projectroutes

funcmain()

ltsmtpgt

Errorsandcrashes

lthtmllang=engt

ltheadgt

lttitlegt

ltheadgt

ltbodygt

ltdivclass=rowgt

ltdivclass=span10gt

lth1gt404lth1gt

ltpgtErrorInfoltpgt

ltdivgt

lt--span--gt

ltdivgt

ltbodygt

lthtmlgt

Anotherexample

Errorsandcrashes

lthtmllang=engt

ltheadgt

lttitlegt

ltheadgt

ltbodygt

ltdivclass=rowgt

ltdivclass=span10gt

ltpgtErrorInfoltpgt

ltdivgt

lt--span--gt

ltdivgt

ltbodygt

lthtmlgt

ifrURLPath==

sayhelloName(wr)

return

NotFound404(wr)

return

sendamessage

Errorsandcrashes

deferfunc()

ifx=recover()x=nil

username=

username=User[uid]

return

Errorsandcrashes

daemon))

-close-fds

-addraddr

-callcall

iferr=nil

logFatalln(err)

err=cmdStart()

iferr=nil

logFatalln(err)

s=bytesTrimSpace(s)

cmdProcessRelease()

cmdProcessKill()

Deployment

packagemain

import(

syscall

varretret2uintptr

varerruintptr

alreadyadaemon

return0

iferr=0

return-1

failure

ifret2lt0

osExit(-1)

ifretgt0

osExit(0)

_=syscallUmask(0)

ifs_errno=0

ifs_retlt0

return-1

ifnochdir==0

osChdir()

ifnoclose==0

ife==nil

fd=fFd()

return0

Deployment

etcsupervisordconf

[unix_http_server]

chmod=0777

chown=rootroot

[inet_http_server]

port=9001

username=admin

[supervisorctl]

[supervisord]

[programblogdemon]

autostart=true

startsecs=5

user=root

Deployment

PackageInstallation

cdrsync-xxx

RsyncConfiguration

Backupandrecovery

binbash

mysql_port=3306

DB2db3)

echo$welcome_msg

usemysql

flag=`echo$`

if[$flag=0]then

flag=`echo$`

if[$flag==0]then

Backupandrecovery

Summary

Buildawebframework

Projectprogram

forkv=rangemuxm

ifpathMatch(kpath)

continue

ifh==nil||len(k)gtn

n=len(k)

Customizedrouters

Storingroutes

regexregexpRegexp

ApplicationApp

Customizedrouters

foripart=rangeparts

expr=([^]+)

expr=part[index]

part=part[index]

params[j]=part

parts[i]=expr

ifregexErr=nil

panic(regexErr)

return

nowcreatetheRoute

routeregex=regex

routeparams=params

StaticDir[url]=path

returnapp

Forwardingroutes

Customizedrouters

AutoRoute

deferfunc()

ifRecoverPanic

gobacktopanic

panic(err)

fori=1i+=1

Critical(fileline)

varstartedbool

started=true

return

findamatchingRoute

continue

values=rURLQuery()

initCall(in)

Customizedrouters

methodCall(in)

ifrMethod==GET

methodCall(in)

elseifrMethod==POST

methodCall(in)

elseifrMethod==HEAD

methodCall(in)

elseifrMethod==PUT

methodCall(in)

ifAutoRender

methodCall(in)

started=true

ifstarted==false

httpNotFound(wr)

Regexmatching

Customizedrouters

CtContext

TpltemplateTemplate

ChildNamestring

TplNamesstring

Layout[]string

TplExtstring

Designcontrollers

cTplNames=

cChildName=cn

cCt=ct

cTplExt=tpl

iflen(cLayout)gt0

iferr=nil

ifcTplNames==

iferr=nil

returnnil

Designcontrollers

packagecontrollers

import(

beegoController

ltDOCTYPEhtmlgt

lthtmlgt

ltheadgt

ltbodygt

lthtmlgt

LinksDirectory

Designcontrollers

const(

LevelTrace=iota

LevelDebug

LevelInfo

LevelWarning

LevelError

LevelCritical

varlevel=LevelTrace

funcLevel()int

returnlevel

logger

funcSetLevel(lint)

level=l

BeeLogger=l

iflevellt=LevelInfo

bComment=[]byte

bEmpty=[]byte

bEqual=[]byte=

bDQuote=[]byte

typeConfigstruct

filenamestring

syncRWMutex

namedfile

iferr=nil

returnnilerr

cfg=ampConfig

fileName()

syncRWMutex

cfgLock()

defercfgUnlock()

deferfileClose()

iferr==ioEOF

continue

commentWrite(line)

commentWriteByte(n)

continue

ifcommentLen()=0

commentReset()

nComment++

cfgoffset[key]=off

returncfgnil

returncdata[key]

funcGetJson()

iferr=nil

return

iferr=nil

appname=hs

maingo

viewtpl

newtpl

layouttpl

indextpl

edittpl

modelsmodelgo

controllers

indexgo

viewgo

deletego

editgo

ShowblogHome

Viewblogdetails

CreateblogBowen

DeleteBowen

EditBowen

CREATETABLEentries(

idINTAUTO_INCREMENT

titleTEXT

contentTEXT

createdDATETIME

primarykey(id)

beegoController

ViewController

beegoController

inputs=thisInput()

NewController

beegoController

thisTplNames=newtpl

inputs=thisInput()

varblogmodelsBlog

EditController

beegoController

inputs=thisInput()

varblogmodelsBlog

DeleteController

beegoController

thisData[Post]=blog

modelsDelBlog(blog)

Modellayer

packagemodels

import(

databasesql

typeBlogstruct

Idint`PK`

Titlestring

Contentstring

CreatedtimeTime

iferr=nil

panic(err)

orm=beedbNew(db)

returnorm

db=GetLink()

dbFindAll(ampblogs)

return

db=GetLink()

return

db=GetLink()

dbSave(ampblog)

returnbg

db=GetLink()

dbDelete(ampblog)

return

Viewlayerlayouttpl

lthtmlgt

ltheadgt

ltstylegt

width200px

floatright

ltstylegt

ltheadgt

ltbodygt

ltulid=menugt

ltulgt

LayoutContent

ltbodygt

lthtmlgt

indextpl

ltulgt

rangeblogs

ltligt

fromCreated

ltligt

ltulgt

viewtpl

PostCreatedltbrgt

PostContent

newtpl

ltformgt

edittpl

ltformgt

Summary

Developwebframework

staticfileserver

wstarted=true

return

Staticfiles

cssfile

jsfile

Picturefiles

Staticfiles

relatedtosession

SessionOn=false

SessionOn=ar

SessionProvider=ar

SessionName=ar

ifSessionOn

Session

return

beegoSessionOn=true

varintcountint

ifcount==nil

intcount=0

intcount=count(int)

intcount=intcount+1

sessGet(count)

Setthesessionvalue

Session

typeUserstruct

formrender()

ltformgt

varuserUser

ifformValidates()

return

lttbodygt

lttrgt

ltthgtNameltthgt

lttrgt

lttdgt

lttrgt

lttdgt

lttrgt

lttdgt

lttrgt

lttdgt

lttrgt

lttdgt

lttrgt

lttdgt

lttrgt

lttdgt

lttrgt

lttdgt

lttrgt

lttdgt

lttrgt

lttbodygt

lttablegt

lttbodygt

lttrgt

ltthgtrulesltthgt

ltthgtExampleltthgt

lttrgt

lttdgt

lttrgt

lttdgt

enreturn

FALSElttdgt

lttrgt

lttdgt

alse(Translators

lttrgt

lttdgt

turnsFALSElttdgt

lttrgt

lttdgt

itreturns

FALSElttdgt

lttrgt

lttdgt

urnsFALSElttdgt

lttrgt

lttdgt

urnsFALSElttdgt

lttrgt

lttdgt

returnsFALSElttdgt

lttrgt

lttdgt

lttrgt

lttdgt

ersitreturns

FALSElttdgt

lttrgt

lttdgt

rthandash

returnsFALSElttdgt

lttrgt

lttdgt

lttrgt

lttdgt

lttrgt

lttdgt

lttrgt

lttdgt

ero)it

lttrgt

lttdgt

ero)it

lttrgt

lttdgt

lttrgt

lttdgt

asinEnglish

lttrgt

lttdgt

lttrgt

lttdgt

characters

returnsFALSElttdgt

lttrgt

lttbodygt

lttablegt

packagecontrollers

import(

ifuser==john

passwordishello

return

beegoController

Uservalidation

1 Letsaddsomeroutes

packagecontrollers

import(

const(

beegoController

Uservalidation

packagecontrollers

import(

nethttp

neturl

beegoController

return

Loginprocess

Uservalidation

varusersmodelsUser

Registrationprocess

thisTplNames=regtpl

fmtPrintln(usererr)

ifusererr==false

return

ifpasserr==false

return

varusersmodelsUser

usersCreated=now

Uservalidation

returnfalse

returntrue

returnfalse

returntrue

ifsess_uid==nil

return

Uservalidation

Translationi18nIL

funcInitLang()

ok=false

varsstring

iflen(args)==1

sok=args[0](string)

s=fmtSprint(args)

ok=false

varsstring

iflen(args)==1

sok=args[0](string)

s=fmtSprint(args)

ok=false

varsstring

iflen(args)==1

sok=args[0](string)

s=fmtSprint(args)

beegoLang=zh

beegoInitLang()

zhjson

submit提交

create创建

enjson

submitSubmit

createCreate

create|Trans

Timetotranslate

time|TransDate

Currencytranslation

money|TransMoney

nethttppprof

runtimepprof

ifPprofOn

packagebeego

import(

nethttppprof

Controller

default

casecmdline

caseprofile

casesymbol

beegoPprofOn=true

(pprof)top10

Total3samples

00010002667mainrun

(pprof)web

Summary

References

preface

AppendixAReferences

preface

Introduction

Installation


Go commands


Summary

Go basic knowledge

Hello Go

Go foundation


struct

Object-oriented

interface

Concurrency

Summary

Web foundation





Summary

HTTP Form

Process form inputs




File upload

Summary

Database


How to use MySQL

How to use SQLite



NOSQL

Summary


Session and cookies


Session storage


Summary

Text files

XML

JSON

Regexp

Templates

Files

Strings

Summary

Web services

Sockets

WebSocket

REST

RPC

Summary


CSRF attacks

Filter inputs

XSS attacks

SQL injection

Password storage


Summary


Time zone

Localized resources

International sites

Summary


Error handling


Write test cases

Summary


Logs

Errors and crashes

Deployment

Backup and recovery

Summary


Project program

Customized routers

Design controllers



Summary


Static files

Session

Form

User validation


pprof

Summary

References

preface

Buildawebframework

Projectprogram

Customizedrouters

Designcontrollers

Summary

Developwebframework

Staticfiles

Session

Uservalidation

Summary

References

preface

Donate

AliPay

alipay

EnglishDonatedonate

BBShttpgocnio

GetStarted

Introduction

11Installation

cdgosrc

allbash

Installation

x86_64GNULinux

Installation

Windows

Usethird-partytools

gvminstallgo183

gvmusego183

apt-get

sudoapt-getupdate

Goenvironment

1 InstallHomebrew

Installation

1 InstallGo

brewinstallgo

Installation

cd$GOPATHsrc

mkdirmymath

$GOPATHandworkspace

packagemymath

fori=0ilt1000i++

z-=(zz-x)(2x)

returnz

mymatha

cd$GOPATHsrc

mkdirmathapp

cdmathapp

vimmaingo

packagemain

import(

mymath

funcmain()

$GOPATHandworkspace

$GOPATH

|-githubcom

|-astaxie

|-beedb

|--$GOOS_$GOARCH

|-githubcom

|-astaxie

|-beedba

mathapp

mymatha

githubcom

astaxie

beedba

mathapp

maingo

mymath

sqrtgo

githubcom

astaxie

beedbgo

utilgo

$GOPATHandworkspace

13Gocommands

Gocommands

Github(git)

Launchpad(Bazaar)

okarchivetar0011s

FAILarchivezip0022s

okcompressgzip0033s

Gocommands

LiteIDEfeatures

Downloadpage

Godevelopmenttools

Sourcecode

Installgocode

GOROOT=cgo

GOBIN=

GOARCH=amd64

GOOS=windows

CGO_ENABLED=1

GOROOT=$HOMEgo

GOBIN=

GOARCH=amd64

GOOS=linux

CGO_ENABLED=1

Godevelopmenttools

Syntaxhighlight

erencesmenu

Godevelopmenttools

1InstallVundle

mkdir~vimbundle

filetypeoffrequired

callvundlebegin()

2InstallVim-go

Pluginfatihvim-go

syntaxon

3 Installgocode

Godevelopmenttools

4 Configuregocode

~updatesh

~gocodeset

2 Installgocode

3 Configuregocode

~updatebash

~gocodeset

Configure~emacsfile

Godevelopmenttools

auto-complete

(ac-config-default)

5 Configureemacs

golangmode

speedbar

(speedbar1)

(add-hook

go-mode-hook

(lambda()

gocode

ImenuampSpeedbar

(func^func()1)))

Outlinemode

Menubar

(requireeasymenu)

(Gotools

[Gorunbuffergot]

(easy-menu-define

go-added-menu

(current-local-map)

Gotools

go-hooked-menu)

helperfunction

(defungo()

runcurrentbuffer

(interactive)

helperfunction

(interactive)

(ifbuffer-read-only

(progn

(ding)

(show-all)

Godevelopmenttools

(progn

matErrorst))

(progn

(erase-buffer)

(progn

helperfunction

(interactive)

(show-all)

gocodeinGithub

Godevelopmenttools

Figure114gdbSetting

Godevelopmenttools

Downloadhttpsatomio

Godevelopmenttools

Summary

Gobasicknowledge

HelloGo

AreyoureadyLetsGo

packagemain

importfmt

funcmain()

HelloGo

funcmain()

HelloGo

varvariableNametype

Gofoundation

_b=3435

packagemain

funcmain()

variint

Moreexamples

constPi=31415926

consti=10000

constMaxThread=10

Elementarytypes

Boolean

samplecode

functest()

Numericaltypes

Gofoundation

varaint8

varbint32

varccomplex64=5+5i

output(5+5i)

String

samplecode

functest()

varsstring=hello

s[0]=c

s=hello

c[0]=c

fmtPrintf(sns2)

s=hello

m=world

fmtPrintf(sna)

andalso

Gofoundation

s=hello

fmtPrintf(sns)

m=`hello

world`

iferr=nil

fmtPrint(err)

Someskills

Definebygroup

Basicform

importfmt

importos

consti=100

constpi=31415

constprefix=Go_

variint

varpifloat32

varprefixstring

Groupform

Gofoundation

import(

const(

pi=31415

prefix=Go_

pifloat32

prefixstring

iotaenumerate

const(

x=iotax==0

y=iotay==1

z=iotaz==2

const(

Somerules

arrayslicemap

vararr[n]type

Gofoundation

b=[10]int123

varfslice[]int

slice=[]byteabcd

Gofoundation

varab[]byte

a=ar[25]

b=ar[35]

defineanarray

definetwoslices

slicefromslice

Slice_a=Array_a[25]

Gofoundation

numbers[ten]=10

numbers[three]=3

Initializeamap

Gofoundation

m[Hello]=Bonjour

newreturnspointers

int320

int640

uint0x0

boolfalse

string

Gofoundation

ifxgt10

fmtPrintln(x)

ifinteger==3

elseifintegerlt3

funcmyFunc()

Herelabelendswith

fmtPrintln(i)

packagemain

importfmt

funcmain()

sum+=index

Printsumisequalto45

forsumlt1000

sum+=sum

forsumlt1000

sum+=sum

ifindex==5

breakorcontinue

fmtPrintln(index)

breakprints109876

forkv=rangemap

for_v=rangemap

yourlogic

switchsExpr

caseexpr1

someinstructions

caseexpr2

caseexpr3

default

othercode

switchi

case234

case10

default

integer=6

switchinteger

fallthrough

default

integerlt=6

integerlt=7

integerlt=8

defaultcase

functionbody

multi-valuereturn

returnvalue1value2

packagemain

importfmt

funcmax(abint)int

ifagtb

returna

returnb

funcmain()

Multi-valuereturn

packagemain

importfmt

returnA+BAB

funcmain()

add=A+B

multiplied=AB

return

Variadicfunctions

funcmyfunc(argint)

for_n=rangearg

packagemain

importfmt

funcadd1(aint)int

funcmain()

packagemain

importfmt

funcadd1(aint)int

funcmain()

funcReadWrite()bool

fileOpen(file)

Dosomework

iffailureX

fileClose()

returnfalse

iffailureY

fileClose()

returnfalse

fileClose()

returntrue

funcReadWrite()bool

fileOpen(file)

deferfileClose()

iffailureX

returnfalse

iffailureY

returnfalse

returntrue

fori=0ilt5i++

deferfmtPrintf(di)

packagemain

importfmt

returninteger2=0

returninteger2==0

varresult[]int

iff(value)

returnresult

funcmain()

PanicandRecover

funcinit()

ifuser==

deferfunc()

ifx=recover()x=nil

b=true

return

import

import(

databasesql

24struct

typepersonstruct

namestring

ageint

Therearetwofields

Letsseehowtouseit

typepersonstruct

namestring

ageint

P=personTom25

struct

packagemain

importfmt

defineanewtype

typepersonstruct

namestring

ageint

ifp1agegtp2age

returnp1p1age-p2age

returnp2p2age-p1age

funcmain()

vartomperson

tomnametomage=Tom18

paul=personPaul43

Letsseeoneexample

struct

packagemain

importfmt

typeHumanstruct

namestring

ageint

weightint

typeStudentstruct

specialtystring

funcmain()

accessfields

markspecialty=AI

markage=46

markweight+=60

markHumanage-=1

struct

packagemain

importfmt

typeSkills[]string

typeHumanstruct

namestring

ageint

weightint

typeStudentstruct

specialtystring

funcmain()

accessfields

modifyembeddedfield

janeint=3

struct

packagemain

importfmt

typeHumanstruct

namestring

ageint

typeEmployeestruct

specialtystring

funcmain()

struct

packagemain

importfmt

typeRectanglestruct

widthheightfloat64

returnrwidthrheight

funcmain()

r1=Rectangle122

r2=Rectangle94

AsRobPikesaid

Syntaxofmethod

Object-oriented

packagemain

import(

typeCirclestruct

radiusfloat64

typeRectanglestruct

widthheightfloat64

method

returnrwidthrheight

funcmain()

c1=Circle10

c2=Circle25

r1=Rectangle94

r2=Rectangle122

Object-oriented

typeageint

typemoneyfloat32

m=months

January31

February28

December31

packagemain

importfmt

const(

WHITE=iota

YELLOW

typeBoxstruct

colorColor

typeColorbyte

method

bcolor=c

method

k=Color(WHITE)

for_b=rangebl

ifbVolume()gtv

v=bVolume()

k=bcolor

returnk

method

fori_=rangebl

method

Object-oriented

returnstrings[c]

funcmain()

boxes=BoxList

Box444RED

Box10101YELLOW

Box1120BLACK

Box10101BLUE

Box10301WHITE

Box202020YELLOW

boxesPaintItBlack()

Inheritanceofmethod

Object-oriented

packagemain

importfmt

typeHumanstruct

namestring

ageint

phonestring

typeStudentstruct

Humananonymousfield

schoolstring

typeEmployeestruct

companystring

func(hHuman)SayHi()

funcmain()

samSayHi()

markSayHi()

Object-oriented

packagemain

importfmt

typeHumanstruct

namestring

ageint

phonestring

typeStudentstruct

schoolstring

typeEmployeestruct

companystring

func(hHuman)SayHi()

funcmain()

samSayHi()

markSayHi()

Object-oriented

26Interface

Whatisaninterface

interface

typeHumanstruct

namestring

ageint

phonestring

typeStudentstruct

schoolstring

loanfloat32

typeEmployeestruct

companystring

moneyfloat32

defineinterfaces

typeMeninterface

SayHi()

Sing(lyricsstring)

SayHi()

Sing(songstring)

SayHi()

Sing(songstring)

func(hHuman)SayHi()

Valueofinterface

interface

packagemain

importfmt

typeHumanstruct

namestring

ageint

phonestring

typeStudentstruct

schoolstring

loanfloat32

typeEmployeestruct

companystring

moneyfloat32

typeMeninterface

SayHi()

Sing(lyricsstring)

method

func(hHuman)SayHi()

method

funcmain()

defineinterfacei

variMen

icanstoreStudent

i=mike

iSayHi()

iSing(Novemberrain)

icanstoreEmployee

iSayHi()

interface

iSing(Borntobewild)

sliceofMen

x=make([]Men3)

for_value=rangex

valueSayHi()

Emptyinterface

varvoidinterface

s=Helloworld

void=i

void=s

String()string

interface

packagemain

import(

strconv

typeHumanstruct

namestring

ageint

phonestring

funcmain()

interface

packagemain

import(

strconv

typeList[]Element

typePersonstruct

namestring

ageint

funcmain()

list=make(List3)

list[0]=1anint

switchtest

interface

packagemain

import(

strconv

typeList[]Element

typePersonstruct

namestring

ageint

funcmain()

list=make(List3)

list[0]=1anint

caseint

casestring

casePerson

default

Embeddedinterfaces

interface

Len()int

Less(ijint)bool

Swap(ijint)

ioReadWriter

Reader

Writer

Reflection

varxfloat64=34

t=reflectTypeOf(x)

v=reflectValueOf(x)

fmtPrintln(typet)

fmtPrintln(valuev)

varxfloat64=34

v=reflectValueOf(x)

vSetFloat(71)

varxfloat64=34

v=pElem()

vSetFloat(71)

interface

gohello(abc)

Letsseeanexample

packagemain

import(

runtime

funcsay(sstring)

fori=0ilt5i++

runtimeGosched()

fmtPrintln(s)

funcmain()

Output

Concurrency

ci=make(chanint)

cs=make(chanstring)

Letsseemoreexamples

packagemain

importfmt

total=0

for_v=rangea

total+=v

funcmain()

a=[]int728-940

c=make(chanint)

gosum(a[len(a)2]c)

fmtPrintln(xyx+y)

Concurrency

ch=make(chantypen)

packagemain

importfmt

funcmain()

fmtPrintln(lt-c)

packagemain

import(

fori=0iltni++

xy=yx+y

close(c)

funcmain()

c=make(chanint10)

fori=rangec

fmtPrintln(i)

Concurrency

packagemain

importfmt

select

caseclt-x

xy=yx+y

caselt-quit

fmtPrintln(quit)

return

funcmain()

c=make(chanint)

quit=make(chanint)

gofunc()

fori=0ilt10i++

fmtPrintln(lt-c)

quitlt-0

fibonacci(cquit)

select

casei=lt-c

default

funcmain()

c=make(chanint)

o=make(chanbool)

gofunc()

select

casev=lt-c

println(v)

println(timeout)

olt-true

Concurrency

runtimeGoexit()

runtimeGosched()

runtimeNumCPU()int

Concurrency

Summary

Webfoundation

pathresourcespath

anchoranchor

browserinformation

blankline

-1xxInformational

-2xxSuccess

-3xxRedirection

-4xxClientError

-5xxServerError

Requestinstance

packagemain

import(

nethttp

strings

forkv=rangerForm

fmtPrintln(keyk)

funcmain()

iferr=nil

HowGoworkswithweb

Buildversiongo112

deferlClose()

rwe=lAccept()

ife=nil

iftempDelay==0

tempDelay=2

tempDelay=max

continue

returne

tempDelay=0

cerr=srvnewConn(rw)

iferr=nil

continue

gocserve()

Detailedworkflow

HowGoworkswithweb

cerr=srvnewConn(rw)

iferr=nil

continue

gocserve()

typeServeMuxstruct

ThestructofmuxEntry

typemuxEntrystruct

hHandler

Getintohttppackage

ServeHTTPcallsf(wr)

muxmuRLock()

defermuxmuRUnlock()

ifh==nil

h=NotFoundHandler()

returnh

packagemain

import(

nethttp

typeMyMuxstruct

ifrURLPath==

sayhelloName(wr)

return

httpNotFound(wr)

return

funcmain()

mux=ampMyMux

Getintohttppackage

samplecode

TODOaddhttp404error

ifrMethod==GET

ifmessage=

message=

ifrMethod==DELETE

ifid==all

dbDeleteAll()

iferr=nil

fmtPrintln(err)

iferr=nil

message=Taskdeleted

Getintohttppackage

Summary

ltformgt

inputelements

ltformgt

HTTPForm

lthtmlgt

ltheadgt

lttitlegtlttitlegt

ltheadgt

ltbodygt

ltformgt

ltbodygt

lthtmlgt

Processforminputs

packagemain

import(

htmltemplate

nethttp

strings

forkv=rangerForm

fmtPrintln(keyk)

ifrMethod==GET

tExecute(wnil)

rParseForm()

logicpartoflogin

funcmain()

iferr=nil

Processforminputs

v=urlValues

vSet(nameAva)

vAdd(friendJess)

vAdd(friendSarah)

vAdd(friendZoe)

Processforminputs

codeforemptyfield

iferr=nil

checkrangeofnumber

ifgetintgt100

toobig

returnfalse

Chinese

Validationofinputs

returnfalse

fmtPrintln(no)

fmtPrintln(yes)

ltselectgt

for_v=rangeslice

returntrue

returnfalse

Radiobuttons

Validationofinputs

slice=[]int12

for_v=rangeslice

returntrue

returnfalse

ifa==nil

returntrue

returnfalse

LinksDirectory

Validationofinputs

importtexttemplate

Output

importhtmltemplate

Output

Crosssitescripting

importhtmltemplate

Output

Crosssitescripting

ifrMethod==GET

h=md5New()

tExecute(wtoken)

loginrequest

rParseForm()

iftoken=

checktokenvalidity

giveerrorifnotoken

lthtmlgt

ltheadgt

ltbodygt

ltformgt

ltbodygt

lthtmlgt

uploadlogic

ifrMethod==GET

h=md5New()

tExecute(wtoken)

iferr=nil

fmtPrintln(err)

return

deferfileClose()

iferr=nil

fmtPrintln(err)

return

deferfClose()

ioCopy(ffile)

Fileupload

Filenamestring

Fileupload

packagemain

import(

ioioutil

mimemultipart

nethttp

iferr=nil

returnerr

openfilehandle

iferr=nil

returnerr

deferfhClose()

iocopy

iferr=nil

returnerr

bodyWriterClose()

iferr=nil

returnerr

iferr=nil

returnerr

returnnil

sampleusage

funcmain()

filename=astaxiepdf

Fileupload

Summary

Database

funcinit()

import(

databasesql

typeDriverinterface

typeConninterface

Close()error

Begin()(Txerror)

typeStmtinterface

Close()error

NumInput()int

driverTx

typeTxinterface

Commit()error

Rollback()error

typeExecerinterface

typeResultinterface

typeRowsinterface

Columns()[]string

Close()error

typeValueinterface

float64

[]byte

timeTime

typeValuerinterface

Value()(Valueerror)

typeDBstruct

driverdriverDriver

dsnstring

closedbool

PRIMARYKEY(`uid`)

packagemain

import(

databasesql

funcmain()

checkErr(err)

insert

checkErr(err)

fmtPrintln(id)

update

HowtouseMySQL

checkErr(err)

fmtPrintln(affect)

checkErr(err)

forrowsNext()

varuidint

varusernamestring

vardepartmentstring

varcreatedstring

checkErr(err)

fmtPrintln(uid)

fmtPrintln(created)

delete

checkErr(err)

reserr=stmtExec(id)

checkErr(err)

fmtPrintln(affect)

dbClose()

iferr=nil

panic(err)

userpassworddbname

HowtouseMySQL

`created`DATENULL

Anexample

packagemain

import(

databasesql

funcmain()

checkErr(err)

insert

checkErr(err)

fmtPrintln(id)

update

checkErr(err)

HowtouseSQLite

checkErr(err)

fmtPrintln(affect)

checkErr(err)

varuidint

varusernamestring

vardepartmentstring

varcreatedtimeTime

forrowsNext()

checkErr(err)

fmtPrintln(uid)

fmtPrintln(created)

delete

checkErr(err)

reserr=stmtExec(id)

checkErr(err)

fmtPrintln(affect)

dbClose()

iferr=nil

panic(err)

ifrowsNext()

checkErr(err)

fmtPrintln(uid)

fmtPrintln(created)

Transactions

HowtouseSQLite

iferr=nil

fmtPrintln(err)

iferr=nil

fmtPrintln(err)

iferr=nil

txRollback()

txCommit()

HowtouseSQLite

CREATETABLEuserinfo

uidserialNOTNULL

Createddate

WITH(OIDS=FALSE)

Anexample

packagemain

import(

databasesql

_githubcomlibpq

const(

DB_USER=postgres

DB_NAME=test

funcmain()

checkErr(err)

deferdbClose()

varlastInsertIdint

HowtousePostgreSQL

checkErr(err)

forrowsNext()

varuidint

varusernamestring

vardepartmentstring

varcreatedtimeTime

checkErr(err)

iferr=nil

panic(err)

HowtousePostgreSQL

import(

databasesql

iferr=nil

panic(err)

orm=beedbNew(db)

HowtousebeedbORM

PostgreSQL

orm=beedbNew(dbpg)

beedbOnDebug=true

typeUserinfostruct

Usernamestring

Departnamestring

CreatedtimeTime

varsaveoneUserinfo

ormSave(ampsaveone)

Insertmultipledata

HowtousebeedbORM

t[username]=astaxie

varuserUserinfo

Example2

varuser2Userinfo

varuser3Userinfo

varuser4Userinfo

HowtousebeedbORM

typeProfilestruct

Nicknamestring

Mobilestring

typeUserinfostruct

Uidint

PK_Usernamestring

Departnamestring

CreatedtimeTime

ProfileHasOne

HowtousebeedbORM

packagemain

import(

ossignal

syscall

PoolredisPool

funcinit()

redisHost=6379

close()

returnampredisPool

MaxIdle3

iferr=nil

returnnilerr

returncerr

_err=cDo(PING)

returnerr

funcclose()

gofunc()

PoolClose()

osExit(0)

conn=PoolGet()

deferconnClose()

vardata[]byte

iferr=nil

returndataerr

funcmain()

testerr=Get(test)

fmtPrintln(testerr)

packagemain

import(

funcmain()

stringmanipulation

val_=clientGet(a)

clientDel(a)

listoperation

vals=[]stringabcde

for_v=rangevals

foriv=rangedbvals

println(istring(v))

clientDel(l)

Installmgo

gogetgopkginmgov2

Hereistheexample

packagemain

import(

gopkginmgov2

gopkginmgov2bson

typePersonstruct

Namestring

Phonestring

funcmain()

iferr=nil

panic(err)

defersessionClose()

iferr=nil

logFatal(err)

result=Person

iferr=nil

logFatal(err)

Summary

Sessionandcookies

typeCookiestruct

Namestring

Valuestring

Pathstring

Domainstring

ExpirestimeTime

RawExpiresstring

MaxAgeint

Securebool

HttpOnlybool

Rawstring

fmtFprint(wcookie)

Sessionandcookies

Sessionmanager

HowtousesessioninGo

typeManagerstruct

providerProvider

maxlifetimeint64

funcinit()

HowtousesessioninGo

itpanics

ifprovider==nil

b=make([]byte32)

return

managerlockLock()

return

rParseForm()

ifrMethod==GET

httpRedirect(wr302)

HowtousesessioninGo

ifcreatetime==nil

ifct==nil

sessSet(countnum1)

Destroysessionid

return

managerlockLock()

Deletesessions

HowtousesessioninGo

funcinit()

managerlockLock()

HowtousesessioninGo

packagememory

import(

containerlist

stvalue[key]=value

returnnil

returnv

returnnil

delete(stvaluekey)

returnnil

returnstsid

typeProviderstruct

locksyncMutexlock

listlistListgc

pderlockLock()

returnnewsessnil

Sessionstorage

returnsesserr

returnnilnil

returnnil

pderlockLock()

ifelement==nil

pderlockLock()

returnnil

funcinit()

import(

Sessionstorage

funcinit()

Sessionstorage

ifct==nil

sessSet(countnum1)

HiNowcount

cookieonlyandtoken

h=md5New()

asktologin

sessSet(tokentoken)

ifcreatetime==nil

Summary

Textfiles

ltservergt

ltserversgt

Samplecode

packagemain

import(

encodingxml

ioioutil

typeserverstruct

funcmain()

iferr=nil

return

deferfileClose()

iferr=nil

return

v=Recurlyservers

iferr=nil

return

fmtPrintln(v)

ltservergt

packagemain

import(

encodingxml

typeServersstruct

typeserverstruct

funcmain()

iferr=nil

ltservergt

ltserversgt

ParseJSON

Parsetostruct

packagemain

import(

encodingjson

typeServerstruct

ServerNamestring

ServerIPstring

Servers[]Server

funcmain()

varsServerslice

127002]`

fmtPrintln(s)

varfinterface

NameWednesday

Parents[]interface

Morticia

forkv=rangem

switchvv=v(type)

casestring

caseint

casefloat64

case[]interface

foriu=rangevv

fmtPrintln(iu)

default

array[123]

float5150

bignum9223372036854775807

stringsimplejson

booltrue

packagemain

import(

encodingjson

typeServerstruct

ServerNamestring

ServerIPstring

Servers[]Server

funcmain()

varsServerslice

berr=jsonMarshal(s)

iferr=nil

Output

typeServerstruct

Example

typeServerstruct

IDwillnotbeoutputed

IDint`json-`

s=Server

ServerName`Go10`

ServerName2`Go10`

ServerIP``

b_=jsonMarshal(s)

osStdoutWrite(b)

Output

returnfalse

returntrue

funcmain()

iflen(osArgs)==1

osExit(1)

fmtPrintln(Number)

Regexp

packagemain

import(

ioioutil

nethttp

regexp

strings

funcmain()

iferr=nil

return

src=string(body)

RemoveSTYLE

RemoveSCRIPT

Regexp

Codesample

Regexp

packagemain

import(

regexp

funcmain()

Findthefirstmatch

sgreaterthan0

Output

thethirdelementuage

for_v=rangesubmatch

SameasFindIndex()

Regexp

SohowdoweuseExpand

funcmain()

src=[]byte(`

callhelloalice

hellobob

callhelloeve

res=[]byte

Regexp

74Templates

Example

Fields

Templates

packagemain

import(

htmltemplate

typePersonstruct

UserNamestring

funcmain()

tExecute(osStdoutp)

typePersonstruct

UserNamestring

Nestedfields

Moreexamples

Templates

packagemain

import(

htmltemplate

typeFriendstruct

Fnamestring

typePersonstruct

UserNamestring

Emails[]string

Friends[]Friend

funcmain()

rangeEmails

anemail

withFriends

myfriendnameisFname

tExecute(osStdoutp)

packagemain

import(

texttemplate

funcmain()

Templates

pipelines

$variable=pipeline

Moreexamples

Templatefunctions

Example

Templates

packagemain

import(

htmltemplate

strings

typeFriendstruct

Fnamestring

typePersonstruct

UserNamestring

Emails[]string

Friends[]Friend

ok=false

varsstring

iflen(args)==1

sok=args[0](string)

s=fmtSprint(args)

findthesymbol

iflen(substrs)=2

returns

replacethebyat

funcmain()

rangeEmails

anemails|emailDeal

withFriends

myfriendnameisFname

tExecute(osStdoutp)

Templates

varbuiltins=FuncMap

andand

callcall

htmlHTMLEscaper

indexindex

jsJSEscaper

lenlength

notnot

printfmtSprint

printffmtSprintf

printlnfmtSprintln

packagemain

import(

texttemplate

funcmain()

Output

ThefirstoneparsedOK

Templates

Maintemplate

headertmpl

defineheader

lthtmlgt

ltheadgt

ltbodygt

contenttmpl

definecontent

templateheader

ltulgt

templatefooter

footertmpl

definefooter

ltbodygt

lthtmlgt

endraw

Templates

packagemain

import(

ioioutil

texttemplate

funcmain()

varallFiles[]string

iferr=nil

fmtPrintln(err)

for_file=rangefiles

filename=fileName()

fmtPrintln()

lttitlegt

Templates

typeTaskstruct

Titlestring

Contentstring

Createdstring

typeContextstruct

Tasks[]Task

Navigationstring

Searchstring

Messagestring

vartask[]typesTask

rangeTasks

Content

Templates

ifTasksrangeTasks

ltdivclass=notegt

lthrgt

ltulgt

ltspangt

ltdivgt

endelse

ltdivclass=notegt

ltdivgt

Templates

Codesample

packagemain

import(

funcmain()

iferr=nil

fmtPrintln(err)

Createandopenfiles

Writeastringtoafile

Codesample

packagemain

import(

funcmain()

userFile=astaxietxt

iferr=nil

return

deferfoutClose()

fori=0ilt10i++

Readdatatob

Codesample

packagemain

import(

funcmain()

userFile=asatxietxt

iferr=nil

return

deferflClose()

n_=flRead(buf)

if0==n

s=[]stringfoobarbaz

Outputfoobarbaz

Output4

Outputbanana

moomoomoo

Strings

Output[abc]

Output[Achtung]

import(fmtstrconv)

packagemain

import(

strconv

funcmain()

e=strconvItoa(1023)

fmtPrintln(abcde)

import(fmtstrconv)

Strings

Summary

Webservices

Sockets

IPtypesinGo

typeIP[]byte

packagemain

import(

funcmain()

iflen(osArgs)=2

osExit(1)

name=osArgs[1]

ifaddr==nil

osExit(0)

Sockets

typeTCPAddrstruct

Portint

HEADHTTP10rnrn

HTTP10200OK

ETag-9985996

Content-Length18074

Connectionclose

Serverlighttpd1423

Clientcode

Sockets

packagemain

import(

ioioutil

funcmain()

iflen(osArgs)=2

osExit(1)

service=osArgs[1]

checkError(err)

osExit(0)

iferr=nil

osExit(1)

TCPserver

Sockets

packagemain

import(

funcmain()

service=7777

checkError(err)

iferr=nil

continue

iferr=nil

osExit(1)

Sockets

packagemain

import(

funcmain()

service=1200

checkError(err)

iferr=nil

continue

deferconnClose()

iferr=nil

osExit(1)

Sockets

packagemain

import(

strconv

funcmain()

service=1200

checkError(err)

iferr=nil

continue

iferr=nil

fmtPrintln(err)

ifread_len==0

iferr=nil

osExit(1)

Sockets

UDPclientcodesample

packagemain

import(

funcmain()

iflen(osArgs)=2

osExit(1)

service=osArgs[1]

checkError(err)

varbuf[512]byte

checkError(err)

osExit(0)

iferr=nil

osExit(1)

Sockets

UDPservercodesample

packagemain

import(

funcmain()

service=1200

checkError(err)

handleClient(conn)

varbuf[512]byte

iferr=nil

return

iferr=nil

osExit(1)

Sockets

WebSocket

Clientcode

lthtmlgt

ltheadgtltheadgt

ltbodygt

varsock=null

consolelog(onload)

functionsend()

socksend(msg)

ltscriptgt

ltformgt

ltbodygt

lthtmlgt

WebSocket

Servercode

packagemain

import(

nethttp

varerrerror

varreplystring

msg=Received+reply

funcmain()

WebSocket

Resources

nlayer

Representation

StateTransfer

Tosummarizetheabove

Figure87RESTslevel

packagemain

import(

nethttp

uid=psByName(uid)

uid=rFormValue(uid)

uid=psByName(uid)

funcmain()

routerGET(Index)

RPCworkingprinciple

Forexample

packagemain

import(

errors

nethttp

netrpc

typeArgsstruct

typeQuotientstruct

QuoRemint

typeArithint

reply=argsAargsB

returnnil

ifargsB==0

quoQuo=argsAargsB

quoRem=argsAargsB

returnnil

funcmain()

arith=new(Arith)

rpcRegister(arith)

rpcHandleHTTP()

iferr=nil

Clientsidecode

packagemain

import(

netrpc

typeArgsstruct

typeQuotientstruct

QuoRemint

funcmain()

iflen(osArgs)=2

osExit(1)

iferr=nil

Synchronouscall

args=Args178

varreplyint

iferr=nil

varquotQuotient

iferr=nil

$http_clocalhost

Arith178=136

packagemain

import(

errors

netrpc

typeArgsstruct

typeQuotientstruct

QuoRemint

typeArithint

reply=argsAargsB

returnnil

ifargsB==0

quoQuo=argsAargsB

quoRem=argsAargsB

returnnil

funcmain()

arith=new(Arith)

rpcRegister(arith)

checkError(err)

iferr=nil

continue

rpcServeConn(conn)

iferr=nil

osExit(1)

Theclientsidecode

packagemain

import(

netrpc

typeArgsstruct

typeQuotientstruct

QuoRemint

funcmain()

iflen(osArgs)=2

osExit(1)

service=osArgs[1]

iferr=nil

Synchronouscall

args=Args178

varreplyint

iferr=nil

varquotQuotient

iferr=nil

JSONRPC

packagemain

import(

errors

netrpc

netrpcjsonrpc

typeArgsstruct

typeQuotientstruct

QuoRemint

typeArithint

reply=argsAargsB

returnnil

ifargsB==0

quoQuo=argsAargsB

quoRem=argsAargsB

returnnil

funcmain()

arith=new(Arith)

rpcRegister(arith)

checkError(err)

iferr=nil

continue

iferr=nil

osExit(1)

Theclientsidecode

packagemain

import(

netrpcjsonrpc

typeArgsstruct

typeQuotientstruct

QuoRemint

funcmain()

iflen(osArgs)=2

logFatal(1)

service=osArgs[1]

iferr=nil

Synchronouscall

args=Args178

varreplyint

iferr=nil

varquotQuotient

iferr=nil

Summary

91CSRFattacks

CSRFattacks

h=md5New()

tExecute(wtoken)

Outputtoken

Authenticationtoken

rParseForm()

iftoken=

Summary

CSRFattacks

secure

Filterinputs

WhoamI

ltselectname=namegt

ltselectgt

ltformgt

rParseForm()

name=rFormGet(name)

CleanMap[name]=name

rParseForm()

Filterinputs

XSSattacks

helloastaxie

http127001

XSSattacks

94SQLinjection

ltformgt

myuserorfoo=foo--

DbExec(sql)

SQLinjection

importcryptosha256

h=sha256New()

importcryptosha1

h=sha1New()

importcryptomd5

h=md5New()

Passwordstorage

packagemain

import(

funcmain()

iferr=nil

logFatal(err)

LinksDirectory

Passwordstorage

packagemain

import(

cryptoaes

cryptocipher

cryptorand

errors

funcmain()

iferr=nil

logFatal(err)

iferr=nil

logFatal(err)

iferr=nil

returnnilerr

iferr=nil

returnnilerr

iferr=nil

returnnilerr

iferr=nil

returnnilerr

typeBlockinterface

BlockSize()int

Summary

Fromthedomainname

ifrHost==wwwastacom

i18nSetLocale(en)

Timezone

ifprefix[0]==en

i18nSetLocale(en)

elseifprefix[0]==cn

elseifprefix[0]==tw

FromURLparameters

Accept-Language

ifAL==en

i18nSetLocale(en)

elseifAL==zh-CN

elseifAL==zh-TW

Timezone

IPAddress

Userprofile

Timezone

packagemain

importfmt

funcmain()

en[pea]=pea

en[bean]=bean

locales[en]=en

cn[pea]=豌豆

cn[bean]=毛豆

locales[zh-CN]=cn

lang=zh-CN

ifv2ok=v[key]ok

returnv2

return

Localizedresources

t=timeNow()

t=tIn(loc)

hourminsec=tClock()

Yreplacedby2012

mreplacedby10

dreplacedby24

en[money]=USDd

cn[money]=￥d元

Localizedresources

|--jsJSfiles

|--cssCSSfiles

indextplUserHome

logintplLogHome

|--images

|--css

indextpl

logintpl

VVLang=lang

jsfile

cssfile

Picturefiles

Localizedresources

zhjson

submit提交

create创建

enjson

submitSubmit

createCreate

Tr=i18nNewLocale()

Outputsubmit

TrSetLocale(zn)

Outputs递交

Internationalsites

iferr=nil

returnerr

deferdirClose()

iferr=nil

returnerr

for_name=rangenames

iferr=nil

returnerr

iffiIsDir()

returnerr

iferr=nil

returnerr

deferfileClose()

returnerr

returnnil

Outputyen1111

1textinformation

Internationalsites

ok=false

varsstring

iflen(args)==1

sok=args[0](string)

s=fmtSprint(args)

VSubmit|T

1 Thedateandtime

ok=false

varsstring

iflen(args)==1

sok=args[0](string)

s=fmtSprint(args)

returnTrTime(s)

VNow|TD

Internationalsites

ok=false

varsstring

iflen(args)==1

sok=args[0](string)

s=fmtSprint(args)

returnTrMoney(s)

VMoney|M

Internationalsites

Summary

iferr=nil

logFatal(err)

typeerrorinterface

Error()string

sstring

returnes

Errorhandling

ifflt0

implementation

ferr=Sqrt(-1)

iferr=nil

fmtPrintln(err)

returnerr

ifanerrorcondition

err=ampSyntaxError

Errorhandling

packagenet

typeErrorinterface

timeSleep(1e9)

continue

iferr=nil

logFatal(err)

funcinit()

record=new(Record)

return

iferr=fn(wr)err=nil

Errorhandling

funcinit()

record=new(Record)

returnerr

typeappErrorstruct

Errorerror

Messagestring

Codeint

cErrorf(veError)

record=new(Record)

returnnil

Summary

Errorhandling

11clt-i

13close(c)

16funcmain()

17msg=Startingmain

18fmtPrintln(msg)

19bus=make(chanint)

delete

DebuggingbyusingGDB

backtrace

30x0000000000000000in()

infolocals

infobreakpoints

infogoroutines

whatis

type=structstring

continue

setvariable

DebuggingbyusingGDB

packagemain

import(

fori=0ilt10i++

close(c)

funcmain()

msg=Startingmain

fmtPrintln(msg)

bus=make(chanint)

msg=startingagofunc

gocounting(bus)

forcount=rangebus

gdbgdbfile

(gdb)run

Startingmain

count0

count1

count2

count3

count4

count5

count6

count7

count8

count9

[LWP2771exited]

DebuggingbyusingGDB

(gdb)b23

(gdb)run

Startingmain

[NewLWP3284]

(gdb)list

18fmtPrintln(msg)

19bus=make(chanint)

21gocounting(bus)

22forcount=rangebus

(gdb)infolocals

count=0

bus=0xf840001a50

(gdb)pcount

(gdb)pbus

(gdb)whatisbus

type=chanint

(gdb)c

Continuing

count0

[NewLWP3303]

(gdb)c

Continuing

count1

DebuggingbyusingGDB

(gdb)infolocals

count=2

bus=0xf840001a50

(gdb)infolocals

count=9

bus=0xf840001a50

(gdb)c

Continuing

count9

(gdb)infogoroutines

(gdb)goroutine1bt

60x0000000000000000in()

DebuggingbyusingGDB

packagegotest

import(

errors

ifb==0

returnabnil

Hereisourtestcode

Writetestcases

packagegotest

import(

testing

exitstatus1

FAILgotest0013s

exitstatus1

FAILgotest0012s

Writetestcases

okgotest0013s

packagegotest

import(

testing

Division(45)

fori=0iltbNi++

Division(45)

okgotest9364s

Writetestcases

Summary

Firstinstallseelog

packagemain

funcmain()

deferlogFlush()

packagelogs

import(

errors

funcloadAppConfig()

appConfig=`

ltsmtpgt

ltfiltergt

ltoutputsgt

ltformatsgt

bySeeloggt

ltformatsgt

ltseeloggt

iferr=nil

fmtPrintln(err)

return

UseLogger(logger)

funcinit()

DisableLog()

loadAppConfig()

funcDisableLog()

Logger=newLogger

DisableLog

LoadAppConfig

Seelog

Outputs

Formats

UseLogger

packagemain

import(

nethttp

projectlogs

projectconfigs

projectroutes

funcmain()

ltsmtpgt

Errorsandcrashes

lthtmllang=engt

ltheadgt

lttitlegt

ltheadgt

ltbodygt

ltdivclass=rowgt

ltdivclass=span10gt

lth1gt404lth1gt

ltpgtErrorInfoltpgt

ltdivgt

lt--span--gt

ltdivgt

ltbodygt

lthtmlgt

Anotherexample

Errorsandcrashes

lthtmllang=engt

ltheadgt

lttitlegt

ltheadgt

ltbodygt

ltdivclass=rowgt

ltdivclass=span10gt

ltpgtErrorInfoltpgt

ltdivgt

lt--span--gt

ltdivgt

ltbodygt

lthtmlgt

ifrURLPath==

sayhelloName(wr)

return

NotFound404(wr)

return

sendamessage

Errorsandcrashes

deferfunc()

ifx=recover()x=nil

username=

username=User[uid]

return

Errorsandcrashes

daemon))

-close-fds

-addraddr

-callcall

iferr=nil

logFatalln(err)

err=cmdStart()

iferr=nil

logFatalln(err)

s=bytesTrimSpace(s)

cmdProcessRelease()

cmdProcessKill()

Deployment

packagemain

import(

syscall

varretret2uintptr

varerruintptr

alreadyadaemon

return0

iferr=0

return-1

failure

ifret2lt0

osExit(-1)

ifretgt0

osExit(0)

_=syscallUmask(0)

ifs_errno=0

ifs_retlt0

return-1

ifnochdir==0

osChdir()

ifnoclose==0

ife==nil

fd=fFd()

return0

Deployment

etcsupervisordconf

[unix_http_server]

chmod=0777

chown=rootroot

[inet_http_server]

port=9001

username=admin

[supervisorctl]

[supervisord]

[programblogdemon]

autostart=true

startsecs=5

user=root

Deployment

PackageInstallation

cdrsync-xxx

RsyncConfiguration

Backupandrecovery

binbash

mysql_port=3306

DB2db3)

echo$welcome_msg

usemysql

flag=`echo$`

if[$flag=0]then

flag=`echo$`

if[$flag==0]then

Backupandrecovery

Summary

Buildawebframework

Projectprogram

forkv=rangemuxm

ifpathMatch(kpath)

continue

ifh==nil||len(k)gtn

n=len(k)

Customizedrouters

Storingroutes

regexregexpRegexp

ApplicationApp

Customizedrouters

foripart=rangeparts

expr=([^]+)

expr=part[index]

part=part[index]

params[j]=part

parts[i]=expr

ifregexErr=nil

panic(regexErr)

return

nowcreatetheRoute

routeregex=regex

routeparams=params

StaticDir[url]=path

returnapp

Forwardingroutes

Customizedrouters

AutoRoute

deferfunc()

ifRecoverPanic

gobacktopanic

panic(err)

fori=1i+=1

Critical(fileline)

varstartedbool

started=true

return

findamatchingRoute

continue

values=rURLQuery()

initCall(in)

Customizedrouters

methodCall(in)

ifrMethod==GET

methodCall(in)

elseifrMethod==POST

methodCall(in)

elseifrMethod==HEAD

methodCall(in)

elseifrMethod==PUT

methodCall(in)

ifAutoRender

methodCall(in)

started=true

ifstarted==false

httpNotFound(wr)

Regexmatching

Customizedrouters

CtContext

TpltemplateTemplate

ChildNamestring

TplNamesstring

Layout[]string

TplExtstring

Designcontrollers

cTplNames=

cChildName=cn

cCt=ct

cTplExt=tpl

iflen(cLayout)gt0

iferr=nil

ifcTplNames==

iferr=nil

returnnil

Designcontrollers

packagecontrollers

import(

beegoController

ltDOCTYPEhtmlgt

lthtmlgt

ltheadgt

ltbodygt

lthtmlgt

LinksDirectory

Designcontrollers

const(

LevelTrace=iota

LevelDebug

LevelInfo

LevelWarning

LevelError

LevelCritical

varlevel=LevelTrace

funcLevel()int

returnlevel

logger

funcSetLevel(lint)

level=l

BeeLogger=l

iflevellt=LevelInfo

bComment=[]byte

bEmpty=[]byte

bEqual=[]byte=

bDQuote=[]byte

typeConfigstruct

filenamestring

syncRWMutex

namedfile

iferr=nil

returnnilerr

cfg=ampConfig

fileName()

syncRWMutex

cfgLock()

defercfgUnlock()

deferfileClose()

iferr==ioEOF

continue

commentWrite(line)

commentWriteByte(n)

continue

ifcommentLen()=0

commentReset()

nComment++

cfgoffset[key]=off

returncfgnil

returncdata[key]

funcGetJson()

iferr=nil

return

iferr=nil

appname=hs

maingo

viewtpl

newtpl

layouttpl

indextpl

edittpl

modelsmodelgo

controllers

indexgo

viewgo

deletego

editgo

ShowblogHome

Viewblogdetails

CreateblogBowen

DeleteBowen

EditBowen

CREATETABLEentries(

idINTAUTO_INCREMENT

titleTEXT

contentTEXT

createdDATETIME

primarykey(id)

beegoController

ViewController

beegoController

inputs=thisInput()

NewController

beegoController

thisTplNames=newtpl

inputs=thisInput()

varblogmodelsBlog

EditController

beegoController

inputs=thisInput()

varblogmodelsBlog

DeleteController

beegoController

thisData[Post]=blog

modelsDelBlog(blog)

Modellayer

packagemodels

import(

databasesql

typeBlogstruct

Idint`PK`

Titlestring

Contentstring

CreatedtimeTime

iferr=nil

panic(err)

orm=beedbNew(db)

returnorm

db=GetLink()

dbFindAll(ampblogs)

return

db=GetLink()

return

db=GetLink()

dbSave(ampblog)

returnbg

db=GetLink()

dbDelete(ampblog)

return

Viewlayerlayouttpl

lthtmlgt

ltheadgt

ltstylegt

width200px

floatright

ltstylegt

ltheadgt

ltbodygt

ltulid=menugt

ltulgt

LayoutContent

ltbodygt

lthtmlgt

indextpl

ltulgt

rangeblogs

ltligt

fromCreated

ltligt

ltulgt

viewtpl

PostCreatedltbrgt

PostContent

newtpl

ltformgt

edittpl

ltformgt

Summary

Developwebframework

staticfileserver

wstarted=true

return

Staticfiles

cssfile

jsfile

Picturefiles

Staticfiles

relatedtosession

SessionOn=false

SessionOn=ar

SessionProvider=ar

SessionName=ar

ifSessionOn

Session

return

beegoSessionOn=true

varintcountint

ifcount==nil

intcount=0

intcount=count(int)

intcount=intcount+1

sessGet(count)

Setthesessionvalue

Session

typeUserstruct

formrender()

ltformgt

varuserUser

ifformValidates()

return

lttbodygt

lttrgt

ltthgtNameltthgt

lttrgt

lttdgt

lttrgt

lttdgt

lttrgt

lttdgt

lttrgt

lttdgt

lttrgt

lttdgt

lttrgt

lttdgt

lttrgt

lttdgt

lttrgt

lttdgt

lttrgt

lttdgt

lttrgt

lttbodygt

lttablegt

lttbodygt

lttrgt

ltthgtrulesltthgt

ltthgtExampleltthgt

lttrgt

lttdgt

lttrgt

lttdgt

enreturn

FALSElttdgt

lttrgt

lttdgt

alse(Translators

lttrgt

lttdgt

turnsFALSElttdgt

lttrgt

lttdgt

itreturns

FALSElttdgt

lttrgt

lttdgt

urnsFALSElttdgt

lttrgt

lttdgt

urnsFALSElttdgt

lttrgt

lttdgt

returnsFALSElttdgt

lttrgt

lttdgt

lttrgt

lttdgt

ersitreturns

FALSElttdgt

lttrgt

lttdgt

rthandash

returnsFALSElttdgt

lttrgt

lttdgt

lttrgt

lttdgt

lttrgt

lttdgt

lttrgt

lttdgt

ero)it

lttrgt

lttdgt

ero)it

lttrgt

lttdgt

lttrgt

lttdgt

asinEnglish

lttrgt

lttdgt

lttrgt

lttdgt

characters

returnsFALSElttdgt

lttrgt

lttbodygt

lttablegt

packagecontrollers

import(

ifuser==john

passwordishello

return

beegoController

Uservalidation

1 Letsaddsomeroutes

packagecontrollers

import(

const(

beegoController

Uservalidation

packagecontrollers

import(

nethttp

neturl

beegoController

return

Loginprocess

Uservalidation

varusersmodelsUser

Registrationprocess

thisTplNames=regtpl

fmtPrintln(usererr)

ifusererr==false

return

ifpasserr==false

return

varusersmodelsUser

usersCreated=now

Uservalidation

returnfalse

returntrue

returnfalse

returntrue

ifsess_uid==nil

return

Uservalidation

Translationi18nIL

funcInitLang()

ok=false

varsstring

iflen(args)==1

sok=args[0](string)

s=fmtSprint(args)

ok=false

varsstring

iflen(args)==1

sok=args[0](string)

s=fmtSprint(args)

ok=false

varsstring

iflen(args)==1

sok=args[0](string)

s=fmtSprint(args)

beegoLang=zh

beegoInitLang()

zhjson

submit提交

create创建

enjson

submitSubmit

createCreate

create|Trans

Timetotranslate

time|TransDate

Currencytranslation

money|TransMoney

nethttppprof

runtimepprof

ifPprofOn

packagebeego

import(

nethttppprof

Controller

default

casecmdline

caseprofile

casesymbol

beegoPprofOn=true

(pprof)top10

Total3samples

00010002667mainrun

(pprof)web

Summary

References

preface

AppendixAReferences

preface

Introduction

Installation


Go commands


Summary

Go basic knowledge

Hello Go

Go foundation


struct

Object-oriented

interface

Concurrency

Summary

Web foundation





Summary

HTTP Form

Process form inputs




File upload

Summary

Database


How to use MySQL

How to use SQLite



NOSQL

Summary


Session and cookies


Session storage


Summary

Text files

XML

JSON

Regexp

Templates

Files

Strings

Summary

Web services

Sockets

WebSocket

REST

RPC

Summary


CSRF attacks

Filter inputs

XSS attacks

SQL injection

Password storage


Summary


Time zone

Localized resources

International sites

Summary


Error handling


Write test cases

Summary


Logs

Errors and crashes

Deployment

Backup and recovery

Summary


Project program

Customized routers

Design controllers



Summary


Static files

Session

Form

User validation


pprof

Summary

References

preface

Donate

AliPay

alipay

EnglishDonatedonate

BBShttpgocnio

GetStarted

Introduction

11Installation

cdgosrc

allbash

Installation

x86_64GNULinux

Installation

Windows

Usethird-partytools

gvminstallgo183

gvmusego183

apt-get

sudoapt-getupdate

Goenvironment

1 InstallHomebrew

Installation

1 InstallGo

brewinstallgo

Installation

cd$GOPATHsrc

mkdirmymath

$GOPATHandworkspace

packagemymath

fori=0ilt1000i++

z-=(zz-x)(2x)

returnz

mymatha

cd$GOPATHsrc

mkdirmathapp

cdmathapp

vimmaingo

packagemain

import(

mymath

funcmain()

$GOPATHandworkspace

$GOPATH

|-githubcom

|-astaxie

|-beedb

|--$GOOS_$GOARCH

|-githubcom

|-astaxie

|-beedba

mathapp

mymatha

githubcom

astaxie

beedba

mathapp

maingo

mymath

sqrtgo

githubcom

astaxie

beedbgo

utilgo

$GOPATHandworkspace

13Gocommands

Gocommands

Github(git)

Launchpad(Bazaar)

okarchivetar0011s

FAILarchivezip0022s

okcompressgzip0033s

Gocommands

LiteIDEfeatures

Downloadpage

Godevelopmenttools

Sourcecode

Installgocode

GOROOT=cgo

GOBIN=

GOARCH=amd64

GOOS=windows

CGO_ENABLED=1

GOROOT=$HOMEgo

GOBIN=

GOARCH=amd64

GOOS=linux

CGO_ENABLED=1

Godevelopmenttools

Syntaxhighlight

erencesmenu

Godevelopmenttools

1InstallVundle

mkdir~vimbundle

filetypeoffrequired

callvundlebegin()

2InstallVim-go

Pluginfatihvim-go

syntaxon

3 Installgocode

Godevelopmenttools

4 Configuregocode

~updatesh

~gocodeset

2 Installgocode

3 Configuregocode

~updatebash

~gocodeset

Configure~emacsfile

Godevelopmenttools

auto-complete

(ac-config-default)

5 Configureemacs

golangmode

speedbar

(speedbar1)

(add-hook

go-mode-hook

(lambda()

gocode

ImenuampSpeedbar

(func^func()1)))

Outlinemode

Menubar

(requireeasymenu)

(Gotools

[Gorunbuffergot]

(easy-menu-define

go-added-menu

(current-local-map)

Gotools

go-hooked-menu)

helperfunction

(defungo()

runcurrentbuffer

(interactive)

helperfunction

(interactive)

(ifbuffer-read-only

(progn

(ding)

(show-all)

Godevelopmenttools

(progn

matErrorst))

(progn

(erase-buffer)

(progn

helperfunction

(interactive)

(show-all)

gocodeinGithub

Godevelopmenttools

Figure114gdbSetting

Godevelopmenttools

Downloadhttpsatomio

Godevelopmenttools

Summary

Gobasicknowledge

HelloGo

AreyoureadyLetsGo

packagemain

importfmt

funcmain()

HelloGo

funcmain()

HelloGo

varvariableNametype

Gofoundation

_b=3435

packagemain

funcmain()

variint

Moreexamples

constPi=31415926

consti=10000

constMaxThread=10

Elementarytypes

Boolean

samplecode

functest()

Numericaltypes

Gofoundation

varaint8

varbint32

varccomplex64=5+5i

output(5+5i)

String

samplecode

functest()

varsstring=hello

s[0]=c

s=hello

c[0]=c

fmtPrintf(sns2)

s=hello

m=world

fmtPrintf(sna)

andalso

Gofoundation

s=hello

fmtPrintf(sns)

m=`hello

world`

iferr=nil

fmtPrint(err)

Someskills

Definebygroup

Basicform

importfmt

importos

consti=100

constpi=31415

constprefix=Go_

variint

varpifloat32

varprefixstring

Groupform

Gofoundation

import(

const(

pi=31415

prefix=Go_

pifloat32

prefixstring

iotaenumerate

const(

x=iotax==0

y=iotay==1

z=iotaz==2

const(

Somerules

arrayslicemap

vararr[n]type

Gofoundation

b=[10]int123

varfslice[]int

slice=[]byteabcd

Gofoundation

varab[]byte

a=ar[25]

b=ar[35]

defineanarray

definetwoslices

slicefromslice

Slice_a=Array_a[25]

Gofoundation

numbers[ten]=10

numbers[three]=3

Initializeamap

Gofoundation

m[Hello]=Bonjour

newreturnspointers

int320

int640

uint0x0

boolfalse

string

Gofoundation

ifxgt10

fmtPrintln(x)

ifinteger==3

elseifintegerlt3

funcmyFunc()

Herelabelendswith

fmtPrintln(i)

packagemain

importfmt

funcmain()

sum+=index

Printsumisequalto45

forsumlt1000

sum+=sum

forsumlt1000

sum+=sum

ifindex==5

breakorcontinue

fmtPrintln(index)

breakprints109876

forkv=rangemap

for_v=rangemap

yourlogic

switchsExpr

caseexpr1

someinstructions

caseexpr2

caseexpr3

default

othercode

switchi

case234

case10

default

integer=6

switchinteger

fallthrough

default

integerlt=6

integerlt=7

integerlt=8

defaultcase

functionbody

multi-valuereturn

returnvalue1value2

packagemain

importfmt

funcmax(abint)int

ifagtb

returna

returnb

funcmain()

Multi-valuereturn

packagemain

importfmt

returnA+BAB

funcmain()

add=A+B

multiplied=AB

return

Variadicfunctions

funcmyfunc(argint)

for_n=rangearg

packagemain

importfmt

funcadd1(aint)int

funcmain()

packagemain

importfmt

funcadd1(aint)int

funcmain()

funcReadWrite()bool

fileOpen(file)

Dosomework

iffailureX

fileClose()

returnfalse

iffailureY

fileClose()

returnfalse

fileClose()

returntrue

funcReadWrite()bool

fileOpen(file)

deferfileClose()

iffailureX

returnfalse

iffailureY

returnfalse

returntrue

fori=0ilt5i++

deferfmtPrintf(di)

packagemain

importfmt

returninteger2=0

returninteger2==0

varresult[]int

iff(value)

returnresult

funcmain()

PanicandRecover

funcinit()

ifuser==

deferfunc()

ifx=recover()x=nil

b=true

return

import

import(

databasesql

24struct

typepersonstruct

namestring

ageint

Therearetwofields

Letsseehowtouseit

typepersonstruct

namestring

ageint

P=personTom25

struct

packagemain

importfmt

defineanewtype

typepersonstruct

namestring

ageint

ifp1agegtp2age

returnp1p1age-p2age

returnp2p2age-p1age

funcmain()

vartomperson

tomnametomage=Tom18

paul=personPaul43

Letsseeoneexample

struct

packagemain

importfmt

typeHumanstruct

namestring

ageint

weightint

typeStudentstruct

specialtystring

funcmain()

accessfields

markspecialty=AI

markage=46

markweight+=60

markHumanage-=1

struct

packagemain

importfmt

typeSkills[]string

typeHumanstruct

namestring

ageint

weightint

typeStudentstruct

specialtystring

funcmain()

accessfields

modifyembeddedfield

janeint=3

struct

packagemain

importfmt

typeHumanstruct

namestring

ageint

typeEmployeestruct

specialtystring

funcmain()

struct

packagemain

importfmt

typeRectanglestruct

widthheightfloat64

returnrwidthrheight

funcmain()

r1=Rectangle122

r2=Rectangle94

AsRobPikesaid

Syntaxofmethod

Object-oriented

packagemain

import(

typeCirclestruct

radiusfloat64

typeRectanglestruct

widthheightfloat64

method

returnrwidthrheight

funcmain()

c1=Circle10

c2=Circle25

r1=Rectangle94

r2=Rectangle122

Object-oriented

typeageint

typemoneyfloat32

m=months

January31

February28

December31

packagemain

importfmt

const(

WHITE=iota

YELLOW

typeBoxstruct

colorColor

typeColorbyte

method

bcolor=c

method

k=Color(WHITE)

for_b=rangebl

ifbVolume()gtv

v=bVolume()

k=bcolor

returnk

method

fori_=rangebl

method

Object-oriented

returnstrings[c]

funcmain()

boxes=BoxList

Box444RED

Box10101YELLOW

Box1120BLACK

Box10101BLUE

Box10301WHITE

Box202020YELLOW

boxesPaintItBlack()

Inheritanceofmethod

Object-oriented

packagemain

importfmt

typeHumanstruct

namestring

ageint

phonestring

typeStudentstruct

Humananonymousfield

schoolstring

typeEmployeestruct

companystring

func(hHuman)SayHi()

funcmain()

samSayHi()

markSayHi()

Object-oriented

packagemain

importfmt

typeHumanstruct

namestring

ageint

phonestring

typeStudentstruct

schoolstring

typeEmployeestruct

companystring

func(hHuman)SayHi()

funcmain()

samSayHi()

markSayHi()

Object-oriented

26Interface

Whatisaninterface

interface

typeHumanstruct

namestring

ageint

phonestring

typeStudentstruct

schoolstring

loanfloat32

typeEmployeestruct

companystring

moneyfloat32

defineinterfaces

typeMeninterface

SayHi()

Sing(lyricsstring)

SayHi()

Sing(songstring)

SayHi()

Sing(songstring)

func(hHuman)SayHi()

Valueofinterface

interface

packagemain

importfmt

typeHumanstruct

namestring

ageint

phonestring

typeStudentstruct

schoolstring

loanfloat32

typeEmployeestruct

companystring

moneyfloat32

typeMeninterface

SayHi()

Sing(lyricsstring)

method

func(hHuman)SayHi()

method

funcmain()

defineinterfacei

variMen

icanstoreStudent

i=mike

iSayHi()

iSing(Novemberrain)

icanstoreEmployee

iSayHi()

interface

iSing(Borntobewild)

sliceofMen

x=make([]Men3)

for_value=rangex

valueSayHi()

Emptyinterface

varvoidinterface

s=Helloworld

void=i

void=s

String()string

interface

packagemain

import(

strconv

typeHumanstruct

namestring

ageint

phonestring

funcmain()

interface

packagemain

import(

strconv

typeList[]Element

typePersonstruct

namestring

ageint

funcmain()

list=make(List3)

list[0]=1anint

switchtest

interface

packagemain

import(

strconv

typeList[]Element

typePersonstruct

namestring

ageint

funcmain()

list=make(List3)

list[0]=1anint

caseint

casestring

casePerson

default

Embeddedinterfaces

interface

Len()int

Less(ijint)bool

Swap(ijint)

ioReadWriter

Reader

Writer

Reflection

varxfloat64=34

t=reflectTypeOf(x)

v=reflectValueOf(x)

fmtPrintln(typet)

fmtPrintln(valuev)

varxfloat64=34

v=reflectValueOf(x)

vSetFloat(71)

varxfloat64=34

v=pElem()

vSetFloat(71)

interface

gohello(abc)

Letsseeanexample

packagemain

import(

runtime

funcsay(sstring)

fori=0ilt5i++

runtimeGosched()

fmtPrintln(s)

funcmain()

Output

Concurrency

ci=make(chanint)

cs=make(chanstring)

Letsseemoreexamples

packagemain

importfmt

total=0

for_v=rangea

total+=v

funcmain()

a=[]int728-940

c=make(chanint)

gosum(a[len(a)2]c)

fmtPrintln(xyx+y)

Concurrency

ch=make(chantypen)

packagemain

importfmt

funcmain()

fmtPrintln(lt-c)

packagemain

import(

fori=0iltni++

xy=yx+y

close(c)

funcmain()

c=make(chanint10)

fori=rangec

fmtPrintln(i)

Concurrency

packagemain

importfmt

select

caseclt-x

xy=yx+y

caselt-quit

fmtPrintln(quit)

return

funcmain()

c=make(chanint)

quit=make(chanint)

gofunc()

fori=0ilt10i++

fmtPrintln(lt-c)

quitlt-0

fibonacci(cquit)

select

casei=lt-c

default

funcmain()

c=make(chanint)

o=make(chanbool)

gofunc()

select

casev=lt-c

println(v)

println(timeout)

olt-true

Concurrency

runtimeGoexit()

runtimeGosched()

runtimeNumCPU()int

Concurrency

Summary

Webfoundation

pathresourcespath

anchoranchor

browserinformation

blankline

-1xxInformational

-2xxSuccess

-3xxRedirection

-4xxClientError

-5xxServerError

Requestinstance

packagemain

import(

nethttp

strings

forkv=rangerForm

fmtPrintln(keyk)

funcmain()

iferr=nil

HowGoworkswithweb

Buildversiongo112

deferlClose()

rwe=lAccept()

ife=nil

iftempDelay==0

tempDelay=2

tempDelay=max

continue

returne

tempDelay=0

cerr=srvnewConn(rw)

iferr=nil

continue

gocserve()

Detailedworkflow

HowGoworkswithweb

cerr=srvnewConn(rw)

iferr=nil

continue

gocserve()

typeServeMuxstruct

ThestructofmuxEntry

typemuxEntrystruct

hHandler

Getintohttppackage

ServeHTTPcallsf(wr)

muxmuRLock()

defermuxmuRUnlock()

ifh==nil

h=NotFoundHandler()

returnh

packagemain

import(

nethttp

typeMyMuxstruct

ifrURLPath==

sayhelloName(wr)

return

httpNotFound(wr)

return

funcmain()

mux=ampMyMux

Getintohttppackage

samplecode

TODOaddhttp404error

ifrMethod==GET

ifmessage=

message=

ifrMethod==DELETE

ifid==all

dbDeleteAll()

iferr=nil

fmtPrintln(err)

iferr=nil

message=Taskdeleted

Getintohttppackage

Summary

ltformgt

inputelements

ltformgt

HTTPForm

lthtmlgt

ltheadgt

lttitlegtlttitlegt

ltheadgt

ltbodygt

ltformgt

ltbodygt

lthtmlgt

Processforminputs

packagemain

import(

htmltemplate

nethttp

strings

forkv=rangerForm

fmtPrintln(keyk)

ifrMethod==GET

tExecute(wnil)

rParseForm()

logicpartoflogin

funcmain()

iferr=nil

Processforminputs

v=urlValues

vSet(nameAva)

vAdd(friendJess)

vAdd(friendSarah)

vAdd(friendZoe)

Processforminputs

codeforemptyfield

iferr=nil

checkrangeofnumber

ifgetintgt100

toobig

returnfalse

Chinese

Validationofinputs

returnfalse

fmtPrintln(no)

fmtPrintln(yes)

ltselectgt

for_v=rangeslice

returntrue

returnfalse

Radiobuttons

Validationofinputs

slice=[]int12

for_v=rangeslice

returntrue

returnfalse

ifa==nil

returntrue

returnfalse

LinksDirectory

Validationofinputs

importtexttemplate

Output

importhtmltemplate

Output

Crosssitescripting

importhtmltemplate

Output

Crosssitescripting

ifrMethod==GET

h=md5New()

tExecute(wtoken)

loginrequest

rParseForm()

iftoken=

checktokenvalidity

giveerrorifnotoken

lthtmlgt

ltheadgt

ltbodygt

ltformgt

ltbodygt

lthtmlgt

uploadlogic

ifrMethod==GET

h=md5New()

tExecute(wtoken)

iferr=nil

fmtPrintln(err)

return

deferfileClose()

iferr=nil

fmtPrintln(err)

return

deferfClose()

ioCopy(ffile)

Fileupload

Filenamestring

Fileupload

packagemain

import(

ioioutil

mimemultipart

nethttp

iferr=nil

returnerr

openfilehandle

iferr=nil

returnerr

deferfhClose()

iocopy

iferr=nil

returnerr

bodyWriterClose()

iferr=nil

returnerr

iferr=nil

returnerr

returnnil

sampleusage

funcmain()

filename=astaxiepdf

Fileupload

Summary

Database

funcinit()

import(

databasesql

typeDriverinterface

typeConninterface

Close()error

Begin()(Txerror)

typeStmtinterface

Close()error

NumInput()int

driverTx

typeTxinterface

Commit()error

Rollback()error

typeExecerinterface

typeResultinterface

typeRowsinterface

Columns()[]string

Close()error

typeValueinterface

float64

[]byte

timeTime

typeValuerinterface

Value()(Valueerror)

typeDBstruct

driverdriverDriver

dsnstring

closedbool

PRIMARYKEY(`uid`)

packagemain

import(

databasesql

funcmain()

checkErr(err)

insert

checkErr(err)

fmtPrintln(id)

update

HowtouseMySQL

checkErr(err)

fmtPrintln(affect)

checkErr(err)

forrowsNext()

varuidint

varusernamestring

vardepartmentstring

varcreatedstring

checkErr(err)

fmtPrintln(uid)

fmtPrintln(created)

delete

checkErr(err)

reserr=stmtExec(id)

checkErr(err)

fmtPrintln(affect)

dbClose()

iferr=nil

panic(err)

userpassworddbname

HowtouseMySQL

`created`DATENULL

Anexample

packagemain

import(

databasesql

funcmain()

checkErr(err)

insert

checkErr(err)

fmtPrintln(id)

update

checkErr(err)

HowtouseSQLite

checkErr(err)

fmtPrintln(affect)

checkErr(err)

varuidint

varusernamestring

vardepartmentstring

varcreatedtimeTime

forrowsNext()

checkErr(err)

fmtPrintln(uid)

fmtPrintln(created)

delete

checkErr(err)

reserr=stmtExec(id)

checkErr(err)

fmtPrintln(affect)

dbClose()

iferr=nil

panic(err)

ifrowsNext()

checkErr(err)

fmtPrintln(uid)

fmtPrintln(created)

Transactions

HowtouseSQLite

iferr=nil

fmtPrintln(err)

iferr=nil

fmtPrintln(err)

iferr=nil

txRollback()

txCommit()

HowtouseSQLite

CREATETABLEuserinfo

uidserialNOTNULL

Createddate

WITH(OIDS=FALSE)

Anexample

packagemain

import(

databasesql

_githubcomlibpq

const(

DB_USER=postgres

DB_NAME=test

funcmain()

checkErr(err)

deferdbClose()

varlastInsertIdint

HowtousePostgreSQL

checkErr(err)

forrowsNext()

varuidint

varusernamestring

vardepartmentstring

varcreatedtimeTime

checkErr(err)

iferr=nil

panic(err)

HowtousePostgreSQL

import(

databasesql

iferr=nil

panic(err)

orm=beedbNew(db)

HowtousebeedbORM

PostgreSQL

orm=beedbNew(dbpg)

beedbOnDebug=true

typeUserinfostruct

Usernamestring

Departnamestring

CreatedtimeTime

varsaveoneUserinfo

ormSave(ampsaveone)

Insertmultipledata

HowtousebeedbORM

t[username]=astaxie

varuserUserinfo

Example2

varuser2Userinfo

varuser3Userinfo

varuser4Userinfo

HowtousebeedbORM

typeProfilestruct

Nicknamestring

Mobilestring

typeUserinfostruct

Uidint

PK_Usernamestring

Departnamestring

CreatedtimeTime

ProfileHasOne

HowtousebeedbORM

packagemain

import(

ossignal

syscall

PoolredisPool

funcinit()

redisHost=6379

close()

returnampredisPool

MaxIdle3

iferr=nil

returnnilerr

returncerr

_err=cDo(PING)

returnerr

funcclose()

gofunc()

PoolClose()

osExit(0)

conn=PoolGet()

deferconnClose()

vardata[]byte

iferr=nil

returndataerr

funcmain()

testerr=Get(test)

fmtPrintln(testerr)

packagemain

import(

funcmain()

stringmanipulation

val_=clientGet(a)

clientDel(a)

listoperation

vals=[]stringabcde

for_v=rangevals

foriv=rangedbvals

println(istring(v))

clientDel(l)

Installmgo

gogetgopkginmgov2

Hereistheexample

packagemain

import(

gopkginmgov2

gopkginmgov2bson

typePersonstruct

Namestring

Phonestring

funcmain()

iferr=nil

panic(err)

defersessionClose()

iferr=nil

logFatal(err)

result=Person

iferr=nil

logFatal(err)

Summary

Sessionandcookies

typeCookiestruct

Namestring

Valuestring

Pathstring

Domainstring

ExpirestimeTime

RawExpiresstring

MaxAgeint

Securebool

HttpOnlybool

Rawstring

fmtFprint(wcookie)

Sessionandcookies

Sessionmanager

HowtousesessioninGo

typeManagerstruct

providerProvider

maxlifetimeint64

funcinit()

HowtousesessioninGo

itpanics

ifprovider==nil

b=make([]byte32)

return

managerlockLock()

return

rParseForm()

ifrMethod==GET

httpRedirect(wr302)

HowtousesessioninGo

ifcreatetime==nil

ifct==nil

sessSet(countnum1)

Destroysessionid

return

managerlockLock()

Deletesessions

HowtousesessioninGo

funcinit()

managerlockLock()

HowtousesessioninGo

packagememory

import(

containerlist

stvalue[key]=value

returnnil

returnv

returnnil

delete(stvaluekey)

returnnil

returnstsid

typeProviderstruct

locksyncMutexlock

listlistListgc

pderlockLock()

returnnewsessnil

Sessionstorage

returnsesserr

returnnilnil

returnnil

pderlockLock()

ifelement==nil

pderlockLock()

returnnil

funcinit()

import(

Sessionstorage

funcinit()

Sessionstorage

ifct==nil

sessSet(countnum1)

HiNowcount

cookieonlyandtoken

h=md5New()

asktologin

sessSet(tokentoken)

ifcreatetime==nil

Summary

Textfiles

ltservergt

ltserversgt

Samplecode

packagemain

import(

encodingxml

ioioutil

typeserverstruct

funcmain()

iferr=nil

return

deferfileClose()

iferr=nil

return

v=Recurlyservers

iferr=nil

return

fmtPrintln(v)

ltservergt

packagemain

import(

encodingxml

typeServersstruct

typeserverstruct

funcmain()

iferr=nil

ltservergt

ltserversgt

ParseJSON

Parsetostruct

packagemain

import(

encodingjson

typeServerstruct

ServerNamestring

ServerIPstring

Servers[]Server

funcmain()

varsServerslice

127002]`

fmtPrintln(s)

varfinterface

NameWednesday

Parents[]interface

Morticia

forkv=rangem

switchvv=v(type)

casestring

caseint

casefloat64

case[]interface

foriu=rangevv

fmtPrintln(iu)

default

array[123]

float5150

bignum9223372036854775807

stringsimplejson

booltrue

packagemain

import(

encodingjson

typeServerstruct

ServerNamestring

ServerIPstring

Servers[]Server

funcmain()

varsServerslice

berr=jsonMarshal(s)

iferr=nil

Output

typeServerstruct

Example

typeServerstruct

IDwillnotbeoutputed

IDint`json-`

s=Server

ServerName`Go10`

ServerName2`Go10`

ServerIP``

b_=jsonMarshal(s)

osStdoutWrite(b)

Output

returnfalse

returntrue

funcmain()

iflen(osArgs)==1

osExit(1)

fmtPrintln(Number)

Regexp

packagemain

import(

ioioutil

nethttp

regexp

strings

funcmain()

iferr=nil

return

src=string(body)

RemoveSTYLE

RemoveSCRIPT

Regexp

Codesample

Regexp

packagemain

import(

regexp

funcmain()

Findthefirstmatch

sgreaterthan0

Output

thethirdelementuage

for_v=rangesubmatch

SameasFindIndex()

Regexp

SohowdoweuseExpand

funcmain()

src=[]byte(`

callhelloalice

hellobob

callhelloeve

res=[]byte

Regexp

74Templates

Example

Fields

Templates

packagemain

import(

htmltemplate

typePersonstruct

UserNamestring

funcmain()

tExecute(osStdoutp)

typePersonstruct

UserNamestring

Nestedfields

Moreexamples

Templates

packagemain

import(

htmltemplate

typeFriendstruct

Fnamestring

typePersonstruct

UserNamestring

Emails[]string

Friends[]Friend

funcmain()

rangeEmails

anemail

withFriends

myfriendnameisFname

tExecute(osStdoutp)

packagemain

import(

texttemplate

funcmain()

Templates

pipelines

$variable=pipeline

Moreexamples

Templatefunctions

Example

Templates

packagemain

import(

htmltemplate

strings

typeFriendstruct

Fnamestring

typePersonstruct

UserNamestring

Emails[]string

Friends[]Friend

ok=false

varsstring

iflen(args)==1

sok=args[0](string)

s=fmtSprint(args)

findthesymbol

iflen(substrs)=2

returns

replacethebyat

funcmain()

rangeEmails

anemails|emailDeal

withFriends

myfriendnameisFname

tExecute(osStdoutp)

Templates

varbuiltins=FuncMap

andand

callcall

htmlHTMLEscaper

indexindex

jsJSEscaper

lenlength

notnot

printfmtSprint

printffmtSprintf

printlnfmtSprintln

packagemain

import(

texttemplate

funcmain()

Output

ThefirstoneparsedOK

Templates

Maintemplate

headertmpl

defineheader

lthtmlgt

ltheadgt

ltbodygt

contenttmpl

definecontent

templateheader

ltulgt

templatefooter

footertmpl

definefooter

ltbodygt

lthtmlgt

endraw

Templates

packagemain

import(

ioioutil

texttemplate

funcmain()

varallFiles[]string

iferr=nil

fmtPrintln(err)

for_file=rangefiles

filename=fileName()

fmtPrintln()

lttitlegt

Templates

typeTaskstruct

Titlestring

Contentstring

Createdstring

typeContextstruct

Tasks[]Task

Navigationstring

Searchstring

Messagestring

vartask[]typesTask

rangeTasks

Content

Templates

ifTasksrangeTasks

ltdivclass=notegt

lthrgt

ltulgt

ltspangt

ltdivgt

endelse

ltdivclass=notegt

ltdivgt

Templates

Codesample

packagemain

import(

funcmain()

iferr=nil

fmtPrintln(err)

Createandopenfiles

Writeastringtoafile

Codesample

packagemain

import(

funcmain()

userFile=astaxietxt

iferr=nil

return

deferfoutClose()

fori=0ilt10i++

Readdatatob

Codesample

packagemain

import(

funcmain()

userFile=asatxietxt

iferr=nil

return

deferflClose()

n_=flRead(buf)

if0==n

s=[]stringfoobarbaz

Outputfoobarbaz

Output4

Outputbanana

moomoomoo

Strings

Output[abc]

Output[Achtung]

import(fmtstrconv)

packagemain

import(

strconv

funcmain()

e=strconvItoa(1023)

fmtPrintln(abcde)

import(fmtstrconv)

Strings

Summary

Webservices

Sockets

IPtypesinGo

typeIP[]byte

packagemain

import(

funcmain()

iflen(osArgs)=2

osExit(1)

name=osArgs[1]

ifaddr==nil

osExit(0)

Sockets

typeTCPAddrstruct

Portint

HEADHTTP10rnrn

HTTP10200OK

ETag-9985996

Content-Length18074

Connectionclose

Serverlighttpd1423

Clientcode

Sockets

packagemain

import(

ioioutil

funcmain()

iflen(osArgs)=2

osExit(1)

service=osArgs[1]

checkError(err)

osExit(0)

iferr=nil

osExit(1)

TCPserver

Sockets

packagemain

import(

funcmain()

service=7777

checkError(err)

iferr=nil

continue

iferr=nil

osExit(1)

Sockets

packagemain

import(

funcmain()

service=1200

checkError(err)

iferr=nil

continue

deferconnClose()

iferr=nil

osExit(1)

Sockets

packagemain

import(

strconv

funcmain()

service=1200

checkError(err)

iferr=nil

continue

iferr=nil

fmtPrintln(err)

ifread_len==0

iferr=nil

osExit(1)

Sockets

UDPclientcodesample

packagemain

import(

funcmain()

iflen(osArgs)=2

osExit(1)

service=osArgs[1]

checkError(err)

varbuf[512]byte

checkError(err)

osExit(0)

iferr=nil

osExit(1)

Sockets

UDPservercodesample

packagemain

import(

funcmain()

service=1200

checkError(err)

handleClient(conn)

varbuf[512]byte

iferr=nil

return

iferr=nil

osExit(1)

Sockets

WebSocket

Clientcode

lthtmlgt

ltheadgtltheadgt

ltbodygt

varsock=null

consolelog(onload)

functionsend()

socksend(msg)

ltscriptgt

ltformgt

ltbodygt

lthtmlgt

WebSocket

Servercode

packagemain

import(

nethttp

varerrerror

varreplystring

msg=Received+reply

funcmain()

WebSocket

Resources

nlayer

Representation

StateTransfer

Tosummarizetheabove

Figure87RESTslevel

packagemain

import(

nethttp

uid=psByName(uid)

uid=rFormValue(uid)

uid=psByName(uid)

funcmain()

routerGET(Index)

RPCworkingprinciple

Forexample

packagemain

import(

errors

nethttp

netrpc

typeArgsstruct

typeQuotientstruct

QuoRemint

typeArithint

reply=argsAargsB

returnnil

ifargsB==0

quoQuo=argsAargsB

quoRem=argsAargsB

returnnil

funcmain()

arith=new(Arith)

rpcRegister(arith)

rpcHandleHTTP()

iferr=nil

Clientsidecode

packagemain

import(

netrpc

typeArgsstruct

typeQuotientstruct

QuoRemint

funcmain()

iflen(osArgs)=2

osExit(1)

iferr=nil

Synchronouscall

args=Args178

varreplyint

iferr=nil

varquotQuotient

iferr=nil

$http_clocalhost

Arith178=136

packagemain

import(

errors

netrpc

typeArgsstruct

typeQuotientstruct

QuoRemint

typeArithint

reply=argsAargsB

returnnil

ifargsB==0

quoQuo=argsAargsB

quoRem=argsAargsB

returnnil

funcmain()

arith=new(Arith)

rpcRegister(arith)

checkError(err)

iferr=nil

continue

rpcServeConn(conn)

iferr=nil

osExit(1)

Theclientsidecode

packagemain

import(

netrpc

typeArgsstruct

typeQuotientstruct

QuoRemint

funcmain()

iflen(osArgs)=2

osExit(1)

service=osArgs[1]

iferr=nil

Synchronouscall

args=Args178

varreplyint

iferr=nil

varquotQuotient

iferr=nil

JSONRPC

packagemain

import(

errors

netrpc

netrpcjsonrpc

typeArgsstruct

typeQuotientstruct

QuoRemint

typeArithint

reply=argsAargsB

returnnil

ifargsB==0

quoQuo=argsAargsB

quoRem=argsAargsB

returnnil

funcmain()

arith=new(Arith)

rpcRegister(arith)

checkError(err)

iferr=nil

continue

iferr=nil

osExit(1)

Theclientsidecode

packagemain

import(

netrpcjsonrpc

typeArgsstruct

typeQuotientstruct

QuoRemint

funcmain()

iflen(osArgs)=2

logFatal(1)

service=osArgs[1]

iferr=nil

Synchronouscall

args=Args178

varreplyint

iferr=nil

varquotQuotient

iferr=nil

Summary

91CSRFattacks

CSRFattacks

h=md5New()

tExecute(wtoken)

Outputtoken

Authenticationtoken

rParseForm()

iftoken=

Summary

CSRFattacks

secure

Filterinputs

WhoamI

ltselectname=namegt

ltselectgt

ltformgt

rParseForm()

name=rFormGet(name)

CleanMap[name]=name

rParseForm()

Filterinputs

XSSattacks

helloastaxie

http127001

XSSattacks

94SQLinjection

ltformgt

myuserorfoo=foo--

DbExec(sql)

SQLinjection

importcryptosha256

h=sha256New()

importcryptosha1

h=sha1New()

importcryptomd5

h=md5New()

Passwordstorage

packagemain

import(

funcmain()

iferr=nil

logFatal(err)

LinksDirectory

Passwordstorage

packagemain

import(

cryptoaes

cryptocipher

cryptorand

errors

funcmain()

iferr=nil

logFatal(err)

iferr=nil

logFatal(err)

iferr=nil

returnnilerr

iferr=nil

returnnilerr

iferr=nil

returnnilerr

iferr=nil

returnnilerr

typeBlockinterface

BlockSize()int

Summary

Fromthedomainname

ifrHost==wwwastacom

i18nSetLocale(en)

Timezone

ifprefix[0]==en

i18nSetLocale(en)

elseifprefix[0]==cn

elseifprefix[0]==tw

FromURLparameters

Accept-Language

ifAL==en

i18nSetLocale(en)

elseifAL==zh-CN

elseifAL==zh-TW

Timezone

IPAddress

Userprofile

Timezone

packagemain

importfmt

funcmain()

en[pea]=pea

en[bean]=bean

locales[en]=en

cn[pea]=豌豆

cn[bean]=毛豆

locales[zh-CN]=cn

lang=zh-CN

ifv2ok=v[key]ok

returnv2

return

Localizedresources

t=timeNow()

t=tIn(loc)

hourminsec=tClock()

Yreplacedby2012

mreplacedby10

dreplacedby24

en[money]=USDd

cn[money]=￥d元

Localizedresources

|--jsJSfiles

|--cssCSSfiles

indextplUserHome

logintplLogHome

|--images

|--css

indextpl

logintpl

VVLang=lang

jsfile

cssfile

Picturefiles

Localizedresources

zhjson

submit提交

create创建

enjson

submitSubmit

createCreate

Tr=i18nNewLocale()

Outputsubmit

TrSetLocale(zn)

Outputs递交

Internationalsites

iferr=nil

returnerr

deferdirClose()

iferr=nil

returnerr

for_name=rangenames

iferr=nil

returnerr

iffiIsDir()

returnerr

iferr=nil

returnerr

deferfileClose()

returnerr

returnnil

Outputyen1111

1textinformation

Internationalsites

ok=false

varsstring

iflen(args)==1

sok=args[0](string)

s=fmtSprint(args)

VSubmit|T

1 Thedateandtime

ok=false

varsstring

iflen(args)==1

sok=args[0](string)

s=fmtSprint(args)

returnTrTime(s)

VNow|TD

Internationalsites

ok=false

varsstring

iflen(args)==1

sok=args[0](string)

s=fmtSprint(args)

returnTrMoney(s)

VMoney|M

Internationalsites

Summary

iferr=nil

logFatal(err)

typeerrorinterface

Error()string

sstring

returnes

Errorhandling

ifflt0

implementation

ferr=Sqrt(-1)

iferr=nil

fmtPrintln(err)

returnerr

ifanerrorcondition

err=ampSyntaxError

Errorhandling

packagenet

typeErrorinterface

timeSleep(1e9)

continue

iferr=nil

logFatal(err)

funcinit()

record=new(Record)

return

iferr=fn(wr)err=nil

Errorhandling

funcinit()

record=new(Record)

returnerr

typeappErrorstruct

Errorerror

Messagestring

Codeint

cErrorf(veError)

record=new(Record)

returnnil

Summary

Errorhandling

11clt-i

13close(c)

16funcmain()

17msg=Startingmain

18fmtPrintln(msg)

19bus=make(chanint)

delete

DebuggingbyusingGDB

backtrace

30x0000000000000000in()

infolocals

infobreakpoints

infogoroutines

whatis

type=structstring

continue

setvariable

DebuggingbyusingGDB

packagemain

import(

fori=0ilt10i++

close(c)

funcmain()

msg=Startingmain

fmtPrintln(msg)

bus=make(chanint)

msg=startingagofunc

gocounting(bus)

forcount=rangebus

gdbgdbfile

(gdb)run

Startingmain

count0

count1

count2

count3

count4

count5

count6

count7

count8

count9

[LWP2771exited]

DebuggingbyusingGDB

(gdb)b23

(gdb)run

Startingmain

[NewLWP3284]

(gdb)list

18fmtPrintln(msg)

19bus=make(chanint)

21gocounting(bus)

22forcount=rangebus

(gdb)infolocals

count=0

bus=0xf840001a50

(gdb)pcount

(gdb)pbus

(gdb)whatisbus

type=chanint

(gdb)c

Continuing

count0

[NewLWP3303]

(gdb)c

Continuing

count1

DebuggingbyusingGDB

(gdb)infolocals

count=2

bus=0xf840001a50

(gdb)infolocals

count=9

bus=0xf840001a50

(gdb)c

Continuing

count9

(gdb)infogoroutines

(gdb)goroutine1bt

60x0000000000000000in()

DebuggingbyusingGDB

packagegotest

import(

errors

ifb==0

returnabnil

Hereisourtestcode

Writetestcases

packagegotest

import(

testing

exitstatus1

FAILgotest0013s

exitstatus1

FAILgotest0012s

Writetestcases

okgotest0013s

packagegotest

import(

testing

Division(45)

fori=0iltbNi++

Division(45)

okgotest9364s

Writetestcases

Summary

Firstinstallseelog

packagemain

funcmain()

deferlogFlush()

packagelogs

import(

errors

funcloadAppConfig()

appConfig=`

ltsmtpgt

ltfiltergt

ltoutputsgt

ltformatsgt

bySeeloggt

ltformatsgt

ltseeloggt

iferr=nil

fmtPrintln(err)

return

UseLogger(logger)

funcinit()

DisableLog()

loadAppConfig()

funcDisableLog()

Logger=newLogger

DisableLog

LoadAppConfig

Seelog

Outputs

Formats

UseLogger

packagemain

import(

nethttp

projectlogs

projectconfigs

projectroutes

funcmain()

ltsmtpgt

Errorsandcrashes

lthtmllang=engt

ltheadgt

lttitlegt

ltheadgt

ltbodygt

ltdivclass=rowgt

ltdivclass=span10gt

lth1gt404lth1gt

ltpgtErrorInfoltpgt

ltdivgt

lt--span--gt

ltdivgt

ltbodygt

lthtmlgt

Anotherexample

Errorsandcrashes

lthtmllang=engt

ltheadgt

lttitlegt

ltheadgt

ltbodygt

ltdivclass=rowgt

ltdivclass=span10gt

ltpgtErrorInfoltpgt

ltdivgt

lt--span--gt

ltdivgt

ltbodygt

lthtmlgt

ifrURLPath==

sayhelloName(wr)

return

NotFound404(wr)

return

sendamessage

Errorsandcrashes

deferfunc()

ifx=recover()x=nil

username=

username=User[uid]

return

Errorsandcrashes

daemon))

-close-fds

-addraddr

-callcall

iferr=nil

logFatalln(err)

err=cmdStart()

iferr=nil

logFatalln(err)

s=bytesTrimSpace(s)

cmdProcessRelease()

cmdProcessKill()

Deployment

packagemain

import(

syscall

varretret2uintptr

varerruintptr

alreadyadaemon

return0

iferr=0

return-1

failure

ifret2lt0

osExit(-1)

ifretgt0

osExit(0)

_=syscallUmask(0)

ifs_errno=0

ifs_retlt0

return-1

ifnochdir==0

osChdir()

ifnoclose==0

ife==nil

fd=fFd()

return0

Deployment

etcsupervisordconf

[unix_http_server]

chmod=0777

chown=rootroot

[inet_http_server]

port=9001

username=admin

[supervisorctl]

[supervisord]

[programblogdemon]

autostart=true

startsecs=5

user=root

Deployment

PackageInstallation

cdrsync-xxx

RsyncConfiguration

Backupandrecovery

binbash

mysql_port=3306

DB2db3)

echo$welcome_msg

usemysql

flag=`echo$`

if[$flag=0]then

flag=`echo$`

if[$flag==0]then

Backupandrecovery

Summary

Buildawebframework

Projectprogram

forkv=rangemuxm

ifpathMatch(kpath)

continue

ifh==nil||len(k)gtn

n=len(k)

Customizedrouters

Storingroutes

regexregexpRegexp

ApplicationApp

Customizedrouters

foripart=rangeparts

expr=([^]+)

expr=part[index]

part=part[index]

params[j]=part

parts[i]=expr

ifregexErr=nil

panic(regexErr)

return

nowcreatetheRoute

routeregex=regex

routeparams=params

StaticDir[url]=path

returnapp

Forwardingroutes

Customizedrouters

AutoRoute

deferfunc()

ifRecoverPanic

gobacktopanic

panic(err)

fori=1i+=1

Critical(fileline)

varstartedbool

started=true

return

findamatchingRoute

continue

values=rURLQuery()

initCall(in)

Customizedrouters

methodCall(in)

ifrMethod==GET

methodCall(in)

elseifrMethod==POST

methodCall(in)

elseifrMethod==HEAD

methodCall(in)

elseifrMethod==PUT

methodCall(in)

ifAutoRender

methodCall(in)

started=true

ifstarted==false

httpNotFound(wr)

Regexmatching

Customizedrouters

CtContext

TpltemplateTemplate

ChildNamestring

TplNamesstring

Layout[]string

TplExtstring

Designcontrollers

cTplNames=

cChildName=cn

cCt=ct

cTplExt=tpl

iflen(cLayout)gt0

iferr=nil

ifcTplNames==

iferr=nil

returnnil

Designcontrollers

packagecontrollers

import(

beegoController

ltDOCTYPEhtmlgt

lthtmlgt

ltheadgt

ltbodygt

lthtmlgt

LinksDirectory

Designcontrollers

const(

LevelTrace=iota

LevelDebug

LevelInfo

LevelWarning

LevelError

LevelCritical

varlevel=LevelTrace

funcLevel()int

returnlevel

logger

funcSetLevel(lint)

level=l

BeeLogger=l

iflevellt=LevelInfo

bComment=[]byte

bEmpty=[]byte

bEqual=[]byte=

bDQuote=[]byte

typeConfigstruct

filenamestring

syncRWMutex

namedfile

iferr=nil

returnnilerr

cfg=ampConfig

fileName()

syncRWMutex

cfgLock()

defercfgUnlock()

deferfileClose()

iferr==ioEOF

continue

commentWrite(line)

commentWriteByte(n)

continue

ifcommentLen()=0

commentReset()

nComment++

cfgoffset[key]=off

returncfgnil

returncdata[key]

funcGetJson()

iferr=nil

return

iferr=nil

appname=hs

maingo

viewtpl

newtpl

layouttpl

indextpl

edittpl

modelsmodelgo

controllers

indexgo

viewgo

deletego

editgo

ShowblogHome

Viewblogdetails

CreateblogBowen

DeleteBowen

EditBowen

CREATETABLEentries(

idINTAUTO_INCREMENT

titleTEXT

contentTEXT

createdDATETIME

primarykey(id)

beegoController

ViewController

beegoController

inputs=thisInput()

NewController

beegoController

thisTplNames=newtpl

inputs=thisInput()

varblogmodelsBlog

EditController

beegoController

inputs=thisInput()

varblogmodelsBlog

DeleteController

beegoController

thisData[Post]=blog

modelsDelBlog(blog)

Modellayer

packagemodels

import(

databasesql

typeBlogstruct

Idint`PK`

Titlestring

Contentstring

CreatedtimeTime

iferr=nil

panic(err)

orm=beedbNew(db)

returnorm

db=GetLink()

dbFindAll(ampblogs)

return

db=GetLink()

return

db=GetLink()

dbSave(ampblog)

returnbg

db=GetLink()

dbDelete(ampblog)

return

Viewlayerlayouttpl

lthtmlgt

ltheadgt

ltstylegt

width200px

floatright

ltstylegt

ltheadgt

ltbodygt

ltulid=menugt

ltulgt

LayoutContent

ltbodygt

lthtmlgt

indextpl

ltulgt

rangeblogs

ltligt

fromCreated

ltligt

ltulgt

viewtpl

PostCreatedltbrgt

PostContent

newtpl

ltformgt

edittpl

ltformgt

Summary

Developwebframework

staticfileserver

wstarted=true

return

Staticfiles

cssfile

jsfile

Picturefiles

Staticfiles

relatedtosession

SessionOn=false

SessionOn=ar

SessionProvider=ar

SessionName=ar

ifSessionOn

Session

return

beegoSessionOn=true

varintcountint

ifcount==nil

intcount=0

intcount=count(int)

intcount=intcount+1

sessGet(count)

Setthesessionvalue

Session

typeUserstruct

formrender()

ltformgt

varuserUser

ifformValidates()

return

lttbodygt

lttrgt

ltthgtNameltthgt

lttrgt

lttdgt

lttrgt

lttdgt

lttrgt

lttdgt

lttrgt

lttdgt

lttrgt

lttdgt

lttrgt

lttdgt

lttrgt

lttdgt

lttrgt

lttdgt

lttrgt

lttdgt

lttrgt

lttbodygt

lttablegt

lttbodygt

lttrgt

ltthgtrulesltthgt

ltthgtExampleltthgt

lttrgt

lttdgt

lttrgt

lttdgt

enreturn

FALSElttdgt

lttrgt

lttdgt

alse(Translators

lttrgt

lttdgt

turnsFALSElttdgt

lttrgt

lttdgt

itreturns

FALSElttdgt

lttrgt

lttdgt

urnsFALSElttdgt

lttrgt

lttdgt

urnsFALSElttdgt

lttrgt

lttdgt

returnsFALSElttdgt

lttrgt

lttdgt

lttrgt

lttdgt

ersitreturns

FALSElttdgt

lttrgt

lttdgt

rthandash

returnsFALSElttdgt

lttrgt

lttdgt

lttrgt

lttdgt

lttrgt

lttdgt

lttrgt

lttdgt

ero)it

lttrgt

lttdgt

ero)it

lttrgt

lttdgt

lttrgt

lttdgt

asinEnglish

lttrgt

lttdgt

lttrgt

lttdgt

characters

returnsFALSElttdgt

lttrgt

lttbodygt

lttablegt

packagecontrollers

import(

ifuser==john

passwordishello

return

beegoController

Uservalidation

1 Letsaddsomeroutes

packagecontrollers

import(

const(

beegoController

Uservalidation

packagecontrollers

import(

nethttp

neturl

beegoController

return

Loginprocess

Uservalidation

varusersmodelsUser

Registrationprocess

thisTplNames=regtpl

fmtPrintln(usererr)

ifusererr==false

return

ifpasserr==false

return

varusersmodelsUser

usersCreated=now

Uservalidation

returnfalse

returntrue

returnfalse

returntrue

ifsess_uid==nil

return

Uservalidation

Translationi18nIL

funcInitLang()

ok=false

varsstring

iflen(args)==1

sok=args[0](string)

s=fmtSprint(args)

ok=false

varsstring

iflen(args)==1

sok=args[0](string)

s=fmtSprint(args)

ok=false

varsstring

iflen(args)==1

sok=args[0](string)

s=fmtSprint(args)

beegoLang=zh

beegoInitLang()

zhjson

submit提交

create创建

enjson

submitSubmit

createCreate

create|Trans

Timetotranslate

time|TransDate

Currencytranslation

money|TransMoney

nethttppprof

runtimepprof

ifPprofOn

packagebeego

import(

nethttppprof

Controller

default

casecmdline

caseprofile

casesymbol

beegoPprofOn=true

(pprof)top10

Total3samples

00010002667mainrun

(pprof)web

Summary

References

preface

AppendixAReferences

preface

Introduction

Installation


Go commands


Summary

Go basic knowledge

Hello Go

Go foundation


struct

Object-oriented

interface

Concurrency

Summary

Web foundation





Summary

HTTP Form

Process form inputs




File upload

Summary

Database


How to use MySQL

How to use SQLite



NOSQL

Summary


Session and cookies


Session storage


Summary

Text files

XML

JSON

Regexp

Templates

Files

Strings

Summary

Web services

Sockets

WebSocket

REST

RPC

Summary


CSRF attacks

Filter inputs

XSS attacks

SQL injection

Password storage


Summary


Time zone

Localized resources

International sites

Summary


Error handling


Write test cases

Summary


Logs

Errors and crashes

Deployment

Backup and recovery

Summary


Project program

Customized routers

Design controllers



Summary


Static files

Session

Form

User validation


pprof

Summary

References

preface

Documents

Table of Contents - WordPress.com · 2018. 3. 2. · Build Web Application with Golang Purpose Because I'm interested in web application development, I used my free time to write