AJAX Transport Layer

Siarhei Barysiuks.barysiuk@sam-solutions.net

Our roadmap

AJAX... not just for toilet cleaning anymore

• AJAX = Asynchronous JavaScript and XML

• Ajax is set of technologies that allow web applications to provide rich interaction without whole page refreshing.

Ajax: Classic Web Application

1) Browser makes request to server2) Server sends HTML/CSS response

Ajax: Ajax Web Application

1) Browser makes request to server asynchronously2) Server sends XML/JSON response3) AJAX Engine processes response

XMLHttpRequest

5) The XMLHttpRequest object receives the XML data and calls a callback to process it.

1) User generates an event (e.g. button click)

2) System creates an XMLHttpRequest and configures with request parameters.

3) The XMLHttpRequest object makes an asynchronous request to the web server.4) Web server returns XML(other) object with data.

XMLHttpRequest: Fetching data flow

// event handler attribute EventListener onreadystatechange;

// state const unsigned short UNSENT = 0; const unsigned short OPENED = 1; const unsigned short HEADERS_RECEIVED = 2; const unsigned short LOADING = 3; const unsigned short DONE = 4; readonly attribute unsigned short readyState;

// request void open(in DOMString method, in DOMString url); void open(in DOMString method, in DOMString url, in boolean async); void open(in DOMString method, in DOMString url, in boolean async, in DOMString user); void open(in DOMString method, in DOMString url, in boolean async, in DOMString user, in DOMString password); void setRequestHeader(in DOMString header, in DOMString value); void send(); void send(in DOMString data); void send(in Document data); void abort();

// response DOMString getAllResponseHeaders(); DOMString getResponseHeader(in DOMString header); readonly attribute DOMString responseText; readonly attribute Document responseXML; readonly attribute unsigned short status; readonly attribute DOMString statusText;

XMLHttpRequest: XHR InterfaceXHR State

opensendabort

Response (Text/XML)

event listener

XMLHttpRequest: How to get XHRfunction getXHR() { var request = null; if (typeof XMLHttpRequest != 'undefined') { request = new XMLHttpRequest(); } else { try { request = new ActiveXObject("Msxml2.XMLHTTP"); } catch (e) { try { request = new ActiveXObject("Microsoft.XMLHTTP"); } catch (e) {} } } return request; }

XMLHttpRequest: Using XHR

var READY_STATE_COMPLETE=4;

var request = getXHR();request.onreadystatechange = function() { if (request.readyState == READY_STATE_COMPLETE) { //200 OK if (request.status == 200) { //process data } //Some error else { //process error } }};request.open(method,url,true);request.send(null);

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XMLHttpRequest: An exampleA classic example is linked drop-downs.

Regions Cities

XMLHttpRequest: Supported methods• GETRequests a representation of the specified resource. By far the most common method used on the Web today.

• POSTSubmits data to be processed (e.g. from an HTML form) to the identified resource. The data is included in the body of the request. This may result in the creation of a new resource or the updates of existing resources or both.

• HEADAsks for the response identical to the one that would correspond to a GET request, but without the response body. This is useful for retrieving meta-information written in response headers, without having to transport the entire content.

• PUTUploads a representation of the specified resource.

• DELETEDeletes the specified resource.

• OPTIONSThis method allows the client to determine the options and/or requirements associated with a resource.

XMLHttpRequest: GET method

var READY_STATE_COMPLETE=4;var request = getXHR();request.onreadystatechange = function() { if (request.readyState == READY_STATE_COMPLETE) { //200 OK if (request.status == 200) { //process data } //Some error else { //process error } }};request.open("GET", "/path?param1=value1&param2=value2",true);

request.send(null);

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is asynchronous?

XMLHttpRequest: POST method

var READY_STATE_COMPLETE=4;var request = getXHR();request.onreadystatechange = function() { if (request.readyState == READY_STATE_COMPLETE) { //200 OK if (request.status == 200) { //process data } //Some error else { //process error } }};request.open("POST", "/path",true);

request.send("param1=value1&param2=value2");

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is asynchronous?

XMLHttpRequest: Features

• object available in IE/Mozilla/Opera/Safari• synchronous and asynchronous requests• POST and GET support

XMLHttpRequest: Pros and Cons

+ not limited to XML+ asynchronous calls+ can receive HTTP status codes/headers+ supported GET and POST

- back button problems- same-origin policy

XMLHttpRequest: Same-origin policyThe philosophy of the same origin policy is simple: the browser should not trust content loaded from arbitrary websites.

The term "origin" is defined using the domain name, protocol and port.

URL Outcome Reason

http://www.example.com/dir2/other.html Success Same protocol and host

http://www.example.com/dir/inner/other.html Success Same protocol and host

http://www.example.com:81/dir2/other.html Failure Same protocol and host but different port

https://www.example.com/dir2/other.html Failure Different protocol

http://en.example.com/dir2/other.html Failure Different host

http://example.com/dir2/other.html Failure Different host

Questions?

iframe transport

iframe transport: Fetching data flow

5) The IFrame object receives the XML data and fires a load event.

1) User generates an event (e.g. button click)

2) System creates a hidden IFrame and configures with request parameters.

3) The IFrame element makes an request to the web server.4) Web server returns XML(other) object with data.

iframe transport: How to use

var iframe = document.createElement("iframe");iframe.width="0";iframe.height="0";...iframe.onload = bind(this.callback, this);...iframe.src = this.url + "?" + this.getRequestString();...document.body.appendChild(this.iframe);

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3GET

{ }In order to use POST you need to create <form> and fill it dynamically.

iframe transport: How to use

var iframe = document.createElement("iframe");iframe.width="0";iframe.height="0";...iframe.onload = bind(this.callback, this);...iframe.src = this.url + "?" + this.getRequestString();...document.body.appendChild(this.iframe);

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GET

<iframe> <!-- ... --> <script type="text/javascript"> window.parent.someFunction(/*data here*/); </script> <!-- ... --></iframe>

iframe transport: An exampleLinked drop-downs example.

Regions Cities

iframe transport: Pros and Cons

+ wide browser compatibility

- browser history- iframe not supported by XHTML strict- cross-domain policy

iframe transport: Cross-domain policy

...iframe.src = this.url + "?" + this.getRequestString();...<iframe> <!-- ... --> <script type="text/javascript"> window.parent.handleIframeResponse(/*data here*/); </script> <!-- ... --></iframe>

different than currenthttp://host:port/path

Questions?

img cookie transport

img cookie transport: What is cookie?Technically, cookies are arbitrary pieces of data chosen by the Web server and sent to the browser.

Relevant count of maximum stored cookies per domain for the major browsers are:

img cookie transport: Cookies limitations

Firefox 2

Firefox 3

Opera 9.30

IE 6

IE 7

Safari

0 12.5 25.0 37.5 50.0

Safari has no limit.

Cookies must be smaller than 4 kilobytes. Internet Explorer imposes a 4KB total for all cookies stored in a given domain.

img cookie transport: Fetching data flow

1) Create <img> with request URL and append it to body. Browser makes a request to the server.

2) Server sets cookies and sends response to the client.

3) Client checks cookies after some time interval.

img cookie transport: An example

...

var img = document.createElement("img");img.width = "0";img.heigth = "0";img.src = this.url + "?" + this.getRequestString(this.data);

...document.body.appendChild(this.img);...

setTimeout(bind(this.callback,this),this.interval);

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img cookie transport: Pros and Cons

+ lightweight+ really really extra wide compatibility

- limited data due to GET and cookie limits

Questions?

script transport

script transport: Fetching data flow

1) Create <script> element with given src attribute. Browser makes request to the server.

2) Server returns JSON data wrapped in function call.

3) Client runs function in own context.

script transport: JSON? What is it?

JSON (JavaScript Object Notation) is a lightweight data-interchange format.

• It is easy for humans to read and write. • It is easy for machines to parse and generate. • It is based on a subset of the JavaScript Programming Language.• It is a text format that is completely language independent.

script transport: JSON? What is it?

{ {"menu": { "id": "file", "value": "File", "popup": { "menuitem": [ {"value": "New", "onclick": "CreateNewDoc()"}, {"value": "Open", "onclick": "OpenDoc()"}, {"value": "Close", "onclick": "CloseDoc()"} ] } } } }

script transport: An example

del.icio.us mashup

script transport: Pros and Cons

+ exempt from Same Origin restriction+ less overhead (headers, cookies)

- JSON only- GET method only

script transport: JSONP extension

Pass a name of callback function as jsonp parameter.

http://somehost:port/path?jsonp=funcName&param1=value1

jsonp + "(" + jsonResult + ");"

Questions?

comet

comet: Intro

Named after kitchen cleaning.

comet: What is it?

Fundamentally, [Comet applications] all use long-lived HTTP connections to reduce the latency with which messages are passed to the server.

In essence, they do not poll the server occasionally. Instead the server has an open line of communication with which it can push data to the client.

comet: Who’s using it?

comet: Classic Ajax Application

comet: Comet Application

comet: An example

Highly interactive applications like chats, real-time games, etc.

comet: Pros and Cons+ low latency+ event-based server push

- client 2 connection limit- pragmatically requires custom server component

CometdLightStreamer...

Questions?