html5 Websockets development guidance

浏览数：23 / 时间：2015年06月09日

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:8000/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>

View Code

Chat.js:

 1 window.onload = function() {
 2 var textView = document.getElementById("text-view");
 3 var buttonSend = document.getElementById("send-button");
 4 var buttonStop = document.getElementById("stop-button");
 5 var label = document.getElementById("status-label");
 6 var socket = new WebSocket("ws://echo.websocket.org");
 7 socket.onopen = function(event) {
 8 label.innerHTML = "Connection open";
 9 }
10 socket.onmessage = function(event) {
11 if (typeof event.data === "string") {
12 label.innerHTML = label.innerHTML + "<br />" + event.data;
13 }
14 }
15 socket.onclose = function(event) {
16 var code = event.code;
17 var reason = event.reason;
18 var wasClean = event.wasClean;
19 if (wasClean) {
20 label.innerHTML = "Connection closed normally.";
21 }
22 else {
23 label.innerHTML = "Connection closed with message: " +
24 reason + " (Code: " + code + ")";
25 }
26 }
27 socket.onerror = function(event) {
28 label.innerHTML = "Error: " + event;
29 }
30 buttonSend.onclick = function() {
31 if (socket.readyState == WebSocket.OPEN) {
32 socket.send(textView.value);
33 }
34 }
35 buttonStop.onclick = function() {
36 if (socket.readyState == WebSocket.OPEN) {
37 socket.close();
38 }
39 }
40 }

View Code

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