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WebSocket emulation - Node.js server
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SockJS-node server

To install sockjs-node run:

npm install sockjs

An simplified echo SockJS server could look more or less like:

var http = require('http');
var sockjs = require('sockjs');

var echo = new sockjs.Server(sockjs_opts);
echo.on('open', function(conn) {
    conn.on('message', function(e) {

var server = http.createServer();
echo.installHandlers(server, {prefix:'[/]echo'});
server.listen(9999, '');

SockJS-node API

The API is highly influenced by the HTML5 Websockets API. The goal is to follow it as closely as possible, but we're not there yet.

Server class

Server class on one side is generating an http handler, compatible with the common Node.js http module.

var sjs = new sockjs.Server(options);

Where options is a hash which can contain:

sockjs_url (required)
Transports which don't support cross-domain communication natively ('eventsource' to name one) use an iframe trick. A simple page is served from the SockJS server (using its foreign domain) and is placed in an invisible iframe. Code run from this iframe doesn't need to worry about cross-domain issues, as it's being run from domain local to the SockJS server. This iframe also does need to load SockJS javascript client library, and this option specifies its url (if you're unsure, point it to the latest minified SockJS client release).
A url prefix for the server. All http requests which paths begins with selected prefix will be handled by SockJS. All other requests will be passed through, to previously registered handlers.
A list of streaming transports that should not be handled by the server. This may be useful, when it's known that the server stands behind a proxy which doesn't like some streaming transports, for example websockets. Valid values are: 'websockets', 'eventsource'.

Server instance

Once you have instantiated Server class you can hook it to the http server instance.

var http_server = http.createServer();
sjs.installHandlers(http_server, options);

Where options can overwrite options set by Server class constructor.

Server instance is an EventEmitter, and emits following event:

A new connection has been successfully opened.

All http requests that don't go under the path selected by prefix will remain unanswered and will be passed to previously registered handlers.

Connection instance

A Connection instance has following methods and properties:

A property describing a state of the connecion.
Sends a message over opened connection. It's illegal to send a message after the connection was closed (either by 'close' method or 'close' event).
close([status], [reason])
Asks the remote client to disconnect. 'status' and 'reason' parameters are optional and can be used to share the reason of disconnection.

A Connection instance is also an EventEmitter, and emits following events:

A message arrived on the connection. Data is available at ''.
Connection was closed. This event is triggered exactly once for every connection.

For example:

sjs.on('open', function(conn) {
    console.log('open' + conn);
    conn.on('close', function(e) {
        console.log('close ' + conn, e);
    conn.on('message', function(e) {
        console.log('message ' + conn,


A fully working echo server does need a bit more boilerplate (to handle unanswered requests), here it is:

var http = require('http');
var sockjs = require('sockjs');

var sockjs_opts = {sockjs_url:

var sjs = new sockjs.Server(sockjs_opts);
sjs.on('open', function(conn) {
    conn.on('message', function(e) {

var server = http.createServer();
server.addListener('request', function(req, res) {
    res.end('404 not found');
server.addListener('upgrade', function(req, con) {

sjs.installHandlers(server, {prefix:'[/]echo'});

server.listen(9999, '');


If you want to see samples of running code, take a look at:

Deployment and load balancing

Often WebSockets don't play nicely with proxies and loadbalancers. Deploying SockJS server behind nginx or apache could be painful.

Fortunetely recent versions of an excellent loadbalancer HAProxy are able to proxy WebSocket connections. We propose to put HAProxy as a front line load balancer and use it to split SockJS traffic from normal HTTP data. Take a look at the sample SockJS HAProxy configuration.

The config also shows how to use HAproxy balancing to split traffic between multiple Node.js servers. You can also do balancing using dns names.

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