LIS651 lecture 3

taming PHP

Thomas Krichel

2005-11-12

functions

• The PHP function reference is available on its web site http://www.php.net/quickref.php. It shows the impressive array of functions within PHP.

• But one of the strengths of PHP is that you can create your own functions as you please.

• If you recreate one of the built-in functions, your own function will have no effect.

example

• Stephanie Rubino was an English teacher and objects to sentences likeYou have ordered 1 bottles of Grosswald Pils.

• Let us define a function rubino_print(). It will take three arguments– a number to check for plural or singular– a word for the singular– a word for the plural

function and parameters

• use the keyword "function" and declare your parameters, as in:function rubino_print ($number, $singular,$plural) {

if($number == 1) {

print "one $singular";

}

else {

print "$number $plural";

}

}

default arguments

• Sometimes you want to allow a function to be called without giving all its arguments. You can do this by declaring a default value. For the previous examplefunction thomas_need($thing='beer') {

print "I need $thing\n";

}

thomas_need(); // prints: I need beer

thomas_need('sex'); // prints: I need sex

rubino_print using common plurals function rubino_print ($num, $sing,$plur=1) { if($num == 1) {

print "one $sing";

}

elseif($plur ==1) {

print "$num $sing"."s";

}

else {

print "$num $plur";

}

}

return value

• Up until now we have just looked at the effect of a function.

• return is a special command that return a value.• When return is used, the function is left.

rubino_print with return

function rubino_print ($number, $singular,$plural) {

if($number == 1) {

return "one $singular";

}

return "$number $plural";

}

$order=rubino_print(2,"beer","beers");

print "you ordered $order\n";

// prints: you ordered 2 beers.

utility function from php.netfunction mysql_fetch_all($query) {

$r=@mysql_query($query);

if($err=mysql_error()) { return $err;}

if(mysql_num_rows($r)) {

while($row=mysql_fetch_array($r)) {$result[]=$row; }

return $result;}}

if(is_array($rows=mysql_fetch_all($query)) {

// do something

}

else { if (! is_null($rows)) {

die("Query failed!");}

}

visibility of variables• variables used inside a function are not visible

from the outside. Example$beer="Karlsberg";

function yankeefy ($name='Sam Adams') {

$beer=$name;

}

yankeefy();

print $beer; // prints: Karlsberg

• the variable inside the function is something different than the variables outside.

accessing global variables.

• There are two ways to change a global variable, i.e. one that is defined in the main script.

• One is just to call it as $GLOBAL['name'] where name is the name of the global variable.function yankeefy ($name="Sam Adams") {

$GLOBAL['beer']="name";

}

brewer_quiz.php: introduction

<?php

$brewers=array('Großwald Brauerei','Homburger Brauhaus', 'Karlsberg Brauerei','Ponter Hausbrauerei', 'Saarfürst Merziger Brauhaus','Mettlacher Abtei-Bräu','Körpricher Landbräu','Brauerei G.A. Bruch','Neufang Brauerei','Zum Stiefel');

$form_top="<form action=\"$_SERVER[PHP_SELF]\" method=\"get\"><p>\n";

$form_submit='<input type="submit" value="I try!"/>'."\n";

$form_end='<input type="hidden" name="submitted" value="1"/></p></form>';

brewer_quiz.php: form building

function build_form($answer,$comment) {

print "<div>Take the Saarland brewery challenge</div>\n";

print $GLOBALS['form_top'];

print "<input type=\"text\" name=\"guess\" value=\"$answer\"/>";

print $GLOBALS['form_submit']; print $GLOBALS['submit_check'];

print $GLOBALS['form_end']; print $comment;

}

brewer_quiz.php: form processingfunction process_form($answer,$brewers) {

$r[]=$answer;

foreach($brewers as $brew) {

if($answer == "$brew") {

$r[]='<div>Congradulation! This is correct!</div>';

return $r;

}

}

$r[]='<div>This is a bad answer, try again!</div>'; return $r;

}

brewer_quiz.php main part

if($_GET['submitted']) {

$from_form=process_form($_GET['guess'],$brewers);

}

build_form($from_form[0],$from_form[1]) ;

?>

working with many source files

• Many times it is useful to split a PHP script into several files.

• PHP has two mechanisms.• require(file) requires the to be included. If the file

is not there, PHP exits with an error.• include(file) includes the file.

require() and include()

• Both assume that you leave PHP. Thus within your included file you can write simple HTML.

• If you want to include PHP in your included file, you have to surround it by <?php and ?>, just like in a PHP script.

• Here is an example to use include to build the basic web page.

top.html

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN"

"http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd">

<html>

<head><title>$title</title>

<meta http-equiv="content-type" content="text/html; charset=UTF-8"/>

<link rel="stylesheet" type="text/css" href="main.css"/>

</head>

<body>

bottom.html

<p id="validator">

<a href="http://validator.w3.org/check?uri=referer"><img

style="border: 0pt"

src="http://wotan.liu.edu/valid-xhtml10.png"

alt="Valid XHTML 1.0!" height="31" width="88" /></a>

</p>

</body>

</html>

validated.php

<?php

$title="my basic page\n";

include("top.html");

print "<div>hello, world</div>";

include("bottom.html");

?>

trouble

• $title in the top.html is not understood as the title. It reads as $title, which means "idiot" for your web user.

• Even if you replace $title with <?php $title ?>

$title is empty. The definition from the outer file is not seen in the included file.

• So you have to split into three files, and print the title in the main file. I leave that to you to figure out.

login.php & create_account.php

• Both require a database that has three fields– id which is an auto_increment int acting as a handle– username is the username of the account. it must be

unique and this is enforced by mySQL– password is a varchar(41) because the sha1 of the

password is stored. This is 40 chars long.

login.phpfunction show_form($message) {

print "<div><h1>$message</h1><h2>Login</h2>

<form action=\"$_SERVER[PHP_SELF]\" method=\"post\">

<div><input type=\"hidden\" name=\"submitted\" value=\"1\" /></div><p>Username <input type=\"text\"

name=\"username\" maxlength=\"15\" value=\"$_POST[username]\" /></p><p>Password <input type=\"password\" name=\"pass\" value=\"$_POST[pass]\"/></p><p><input type=\"submit\" value=\"Login\" /> Not yet a member? <a href=\"create_account.php\">Create an account</a>!

</p></form></div>";

}

function process_form() {

$username=trim($_POST['username']);

$pass=trim($_POST['pass']);

$sha_pass=sha1($pass);

$db=mysql_connect('localhost','krichel','laempel');

$query="SELECT * FROM beer_shop.users WHERE

username='$username' AND password = '$sha_pass'";

$result=mysql_query($query);

$error=mysql_error();

if($error) { return "Sorry: $query gives an error<br/>

$error"; }

$affected=mysql_affected_rows();

if(! ($affected)) {return "Invalid username or password";}

}

login.php (end)

if($_POST['submitted']) {

$error=process_form();

if($error) { show_form($error); }

else {

$user=$_POST['username'];

print "<h1>Welcome to $user</h1>";

}

}

else { show_form(''); }

create_account.php

function show_form($message) {

print "<div><h1>$message</h1><h2>Create

Account</h2><p>Please complete the form below to create

your account. </p> <form action=\"$_SERVER[PHP_SELF]

\" method=\"post\"><div><input type=\"hidden\"

name=\"submitted\" value=\"1\" /></div> It must be more

than 5 characters and cannot be your username.</p><p>

<input type=\"submit\" value=\"Create Account\" />

</p></form></div>";

create_account.php

<h3>Password</h3><p> Password <input type=\"password\"

name=\"pass1\" value=\"$_POST[pass1]\"/>Confirm

Password <input type=\"password\" name=\"pass2\"

value=\"$_POST[pass2]\"/> </p><p>The password you enter

will be used to access your account. It must be more than 5

characters and cannot be your username.</p> <p><input

type=\"submit\" value=\"Create Account\"

/></p></form></div>";

}

create_account.phpfunction process_form() {

$username=trim($_POST['username']);

$pass1=trim($_POST['pass1']);

$pass2=trim($_POST['pass2']);

if(strlen($username)<6) {

return "Username is too short.";

}

if(! ($pass1 == $pass2)) {return "Passwords do not match.";}

$pass=$pass1;

if($pass == $username) {

return "Your username can not be your password.";

create_account.php if(strlen($pass)<6) {return "Password is too short.";}

$sha_pass=sha1($pass);

$db=mysql_connect('localhost','krichel','laempel');

$query="INSERT INTO beer_shop.users VALUES ('','$username','$sha_pass')";

$result=mysql_query($query);

$error=mysql_error();

if($error == "Duplicate entry '$username' for key 2") { return "Sorry: Username $username is already taken, choose another.";

}

else {print "<h1>Thank you for registering with us!</h1>";}

}

1

create_account.php (end)

if($_POST['submitted']) {

$error=process_form();

if($error) {

show_form($error);

}

}

else {

show_form('');

}

sessions

• You will recall that HTTP is a stateless protocol. Each request/response is self-contained.

• Statefulness is crucial in Web applications. Otherwise users have to authenticate every time they access a new page.

• Traditionally, one way to create statefullness is to use cookies.

• PHP uses cookies to create a concept of its own, sessions, that makes it all very easy.

cookies

• A cookie is a piece of attribute/value data. A server can send cookies as value of a HTTP header Set-Cookie:. Multiple headers may be sent.

• When the client visits the web site again, it will send the cookie back to the server with a HTTP header Cookie:

Set-Cookie• Set-Cookie: name=value; [expires= date;]

[path=path;] [domain= domain] [secure]• where

– name= is the variable name set in the cookie– value= is the variable's value– date= is a date when the cookie expires– path= restricts the cookie to be sent only when requests

to a path starting with path are made– domain= restricts the sending of the cookie to a certain

domain– secure restricts transmission to https

Cookies:

• The browser compares the request it wants to make with the URL and the domain that sent the cookie.

• If the path is not set the cookie will only be sent to a request with the originating URL.

• If the cookie matches the request a request header of the form

Cookie: name1=value1 ; name2=value2

is sent.

sessions

• Sessions are a feature of PHP. PHP remembers a session through a special cookie PHPSESSID.

• To activate the sessions, include session_start(); at the beginning of your script, before any printing has been done.

• One a session is active, you have a special super-global variable $_SESSION. Session data is stored in special files on wotan.

$_SESSION

• This is an array where you can read and set variables that you want to keep during the session.if($_SESSION[user_name]) {

print "welcome $_SESSION[user_name]";

}

else {

// show users login form

print login_form();

}

ending sessions

• At 9 and 39 past each hour, wotan deletes all session files that have not been changed for 24 minutes or more.

• If you want to remove a session yourself, you can call session_destroy() in your script.

visit.php<?php

$top='<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN"

"http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd">

<html><head><title></title><meta http-equiv="content-type"

content="text/html; charset=UTF-8"/>

</head><body><div>';

$bottom='</div><p>

<a href="http://validator.w3.org/check?uri=referer">

<img style="border: 0pt" src="/valid-xhtml10.png"

alt="Valid XHTML 1.0!" height="31" width="88" />

</a></p></body></html>';

visit.phpsession_start();

$current=mktime(); // look at the current time

if($_SESSION[last_click]) {

$passed=$current-$_SESSION[last_click];

$to_print.="$passed seconds have passed since your last visit.\n";

$_SESSION[last_click]=$current;

} else {

$to_print="This is your first visit.\n";

$_SESSION[last_click]=$current;

}

print "$top\n$to_print\n$bottom";

?>

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