Node: Up and Running

Socket.IO

Socket.IO is a simple little library that’s a lot like Node’s core net library. Socket.IO allows you to send messages back and forth with browser clients that connect with your Node server, using an efficient, low-level socket mechanism. One of the nice things about the module is that it provides a shared interface between the browser and the server. That is, you can write the same JavaScript on both in order to do messaging work once you have a connection established.

Socket.IO is so named because it supports the HTML5 WebSockets standard on browsers that support it (and have it enabled). Fortunately, the library also supports a number of fallbacks:

• WebSocket

• WebSocket over Flash

• XHR Polling

• XHR Multipart Streaming

• Forever Iframe

• JSONP Polling

These options ensure that you’ll be able to have some kind of persistent connection to the browser in almost any environment. The Socket.IO module includes the code to power these connection paths on both the browser and the server side with the same API.

Instantiating Socket.IO is as simple as including the module and creating a server. One of the things that’s a little different about Socket.IO is that it requires an HTTP server as well; see Example 7-16.

Example 7-16. Creating a Socket.IO server

 var http = require('http'), io = require('socket.io'); server = http.createServer(); server.on('request', function(req, res){ //Typical HTTP server stuff res.writeHead(200, {'Content-Type': 'text/plain'}); res.end('Hello World'); }); server.listen(80); ...