If you are making a web application which needs to update client in realtime, you can use this example to quickly write such an application in
nodejs
using socket.io
. Redis pubsub
is used as a data source in this example. You can use any other data source.Since these kind of applications are event-driven on server side (for example, a new message arrived for user) it is a good idea to use nodejs.
Socket.io(http://socket.io) is used to maintain connection with the user. It uses websockets if available else uses fallback machanisms like long-polling. For more details see https://github.com/LearnBoost/socket.io-spec
Requirements
- redis
- nodejs
- nodejs redis module
- nodejs socket.io module
Installation
For installing
redis
visit http://redis.io/downloadFor installing
nodejs
visit http://nodejs.org/downloadIf you are on linux, you can use package manager of your distribution to install
redis
and nodejs
.Use npm to install nodejs dependencies
You may want to use
hiredis
on production as explained on project page https://github.com/mranney/node_redis.Usage
Start the server by
Now hit
http://localhost
on your browserServer side flow
When the server starts, an http handler is created whose only task currently is to server index.html.
There is socket.io handler which listens to all the websocket connections and manages them. It subscribes them to appropricate rooms and sends updates.
Lastly there are two redis clients one of which subscribes to channels on redis and as soon as a message is received, it broadcasts them in appropricate rooms. The second client simply publishes dummy updates to redis channels to which the first redis client is subscribed to.
Client side flow
As soon as the page load is done, socket.io client tries to connect to the server and on connection sends subscribe message for a particular channel. When updates are received it displays them
I have documented the code as extensively as I could. Please email me in case of doubts.
In one of my previous posts I wrote about Real time notifications with PHP. I wanted to create a simple comet system fully written in PHP and JavaScript. It worked but as Scott Mattocks told me in a comment this implementation was still just doing short polling. The performance with this solution may be bad in a medium/hight traffic site. This days I’m playing with node.js and I want to create a simple test. I want to do exactly the same than the previous post but now with node.js instead of my PHP+js test. Let’s start
Now I want to use socket.io instead of pure web-sockets like my previous posts about node.js. For those who don’t know, socket.io is amazing library that allows us to use real-time technologies within every browsers (yes even with IE6). It uses one technology or another depending on the browser we are using, with the same interface for the developer. That’s means if we’re using Google Chrome we will use websockets, but if our browser does’t support them, socket.io will choose another supported transports. Definitely socket.io is the jQuery of the websockets. The supporter transports are:
- WebSocket
- Adobe Flash Socket
- AJAX long polling
- AJAX multipart streaming
- Forever Iframe
- JSONP Polling
First we create our node.js server. A really simple one.
Socket Io Client
Iphone 5s quick user guide. This server will broadcast the message received from the browser to all connected clients.
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Our HTML page will look like that:
As we can see we are including the js script called socket.io/socket.io.js. This script is served by our node server.
In fact we can use our node.js to serve everything (HTML, js, CSS) but in our example we will use only node.js for real-time stuff. Apache will serve the rest of the code (only a HTML file in this case).
And that’s all. Those few lines perform the same thing than our PHP and js code in the other post’s example. Our node.js implementation is definitely smarter than the PHP one. The socket.io library also allows us to use the example with all browser. Same code and without any browser nightmare (just like jQuery when we work with DOM).
Here I have a little screencast with the working example. As we will see there We will connect to the node server with firefox and chrome. Firefox will use xhr multipart and Chrome will use Websokets.
Another important issue of socket.io library is that we forget about the reconnection to the web-socket server, if something wrong happens (as we can see in Real time monitoring PHP applications with web-sockets and node.js). If we use raw WebSocket implementations and our connection with the web-socket server crashes or if we stop the server, our application will raise disconnect event and we need to create something to reconnect to the server. socket.io does it for us. With our small piece of JavaScript code we will get a high performance real-time applicatrion. Node is cool. Really cool. Kinda wierd at the beginning but the learning effort will be worthwhile. A few js lines and a real time applications.
I’ve got a problem within our node.js application. If we’ve got some kind of security within our application (imagine for example it’s behind a session based auth form) we need to share this security layer with our node.js server to ensure that non authenticated users aren’t allowed to use our websockets. I don’t know how to do it just now, but I’m investigating. Do you have any idea?
Full code Code at github. Ensure you’re using the stable version of node.js. With the last versión available on github of node.js there’s a bug and server dies when we connect with Google Chrome.
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