1. WebSockets -- full-duplex communication

The main HTML5 pillars include Markup, CSS3, and JavaScript APIs

For whole set of HTML5, visit html5rocks.com (google product)

 

The URL

The following image shows the WebSocket URL example in tokens:

schema      host              port     server

   ws://example.com:/chat.php

wss is supported as well and is the WebSocket equivalent to https for secure connections (SSL).

Who's using WebSockets

Name            Website                                            Description

Gamooga       http://www.gamooga.com/                  Real-time backend for apps and games

GitLive           http://gitlive.com/                               Notifications on GitHub projects

Superfeedr     http://superfeedr.com/                       Real-time data pushing

Pusher           http://pusher.com/                             Scalable real-time functionality API for web and mobile apps

Smarkets       https://smarkets.com/                        Real-time betting

IRC Cloud      https://www.irccloud.com/                   Chatting

Two great resources containing a large variety of WebSocket demos are as follows:

• http://www.websocket.org/demos.html

• http://www.html5rocks.com/en/features/connectivity

2. The WebSocket API web client

WebSocket communication and data transmission is bidirectional, so we need two parties to establish it: a server and a client.

HTML5 basics:

  • Markup HTML (.html)

For more information about the HTML5 markup, consider visiting http://html5doctor.com/. There is a complete reference for the supported HTML5 tags at http://html5doctor.com/element-index/.

  • Styling CSS (.css)

http://www.css3.info/ is a great resource for CSS3 and further reading.

  • Logic JavaScript (.js)

The markup defines the structure and the CSS rules apply the styling. What about event handling and user actions? Well, here comes JavaScript! The WebSocket API is pure JavaScript, too!

WebSocket API allows you to connect to a local or remote server, listen for messages, send data, and close the connection. Typical WebSocket workflow shows below:

JavaScript provides an easy way to find out whether a browser can execute WebSocket-specific code:

if (window.WebSocket) {   // validation check

　　console.log("WebSockets supported.");                                               

　　// Continue with the rest of the WebSockets-specific functionality…

}

else {

　　console.log("WebSockets not supported.");

　　alert("Consider updating your browser for a richer experience.");

}

Want to see which browsers do support the WebSocket protocol? There is an up-to-date resource available at http://caniuse.com/#feat=websockets.

  • The WebSocket object ：var socket = new WebSocket("ws://echo.websocket.org");
  • Events: Open, Message, Close, and Error.

You can handle them either by implementing the onopen, onmessage, onclose, and onerror functions respectively, or by using the addEventListener method.

  • Actions: The WebSocket protocol supports two main actions: send() and close().
  • Properties:

Properties               Description

url                            Returns the URL of the WebSocket  protocol Returns the protocol used by the server

readyState                Reports the state of the connection and can take one of the following selfexplanatory values:

　　　　　　　　　　　　　　WebSocket.OPEN

　　　　　　　　　　　　　　WebSocket.CLOSED

　　　　　　　　　　　　　　WebSocket.CONNECTING

　　　　　　　　　　　　　　WebSocket.CLOSING

bufferedAmount     Returns the total number of bytes that were queued when the send() method was called

binaryType             Returns the binary data format we

received                  when the onmessage event was raised

 The complete client example:

index.html:

<!DOCTYPE html>

<html>

<head>

<title>HTML5 WebSockets</title>

<link rel="stylesheet" href="style.css" />

<script src="chat.js"></script>

</head>

<body>

<h1> HTML5 WebSocket chat. </h1>

<input type="text" id="text-view" />

<input type="button" id="send-button" value="Send!" />

<input type="button" id="stop-button" value="Stop" />

</br>

<label id="status-label">Status</label>

</body>

</html>

Chat.js:

 window.onload = function() {

 var textView = document.getElementById("text-view");

 var buttonSend = document.getElementById("send-button");

 var buttonStop = document.getElementById("stop-button");

 var label = document.getElementById("status-label");

 var socket = new WebSocket("ws://echo.websocket.org");

 socket.onopen = function(event) {

 label.innerHTML = "Connection open";

 }

 socket.onmessage = function(event) {

 if (typeof event.data === "string") {

 label.innerHTML = label.innerHTML + "<br />" + event.data;

 }

 }

 socket.onclose = function(event) {

 var code = event.code;

 var reason = event.reason;

 var wasClean = event.wasClean;

 if (wasClean) {

 label.innerHTML = "Connection closed normally.";

 }

 else {

 label.innerHTML = "Connection closed with message: " +

 reason + " (Code: " + code + ")";

 }

 }

 socket.onerror = function(event) {

 label.innerHTML = "Error: " + event;

 }

 buttonSend.onclick = function() {

 if (socket.readyState == WebSocket.OPEN) {

 socket.send(textView.value);

 }

 }

 buttonStop.onclick = function() {

 if (socket.readyState == WebSocket.OPEN) {

 socket.close();

 }

 }

 }

Server side:

Server                                                                  Client
Create a server on localhost:8181  
Start running
Initial handshake: establish connection  <----------- Request connection
Handle the incoming message  --------------------> Send message

refer to book (p. 31):http://www.amazon.com/Getting-Started-HTML5-WebSocket-Programming/dp/1782166963

create dll file in c#

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