Table of contents

• SockJS-cyclone
  • What is SockJS?
  • What is Cyclone?
  • How does it look like?
  • Multiplexing
• Installation
• SockJS-cyclone API
  • SockJSConnection
  • SockJSRouter
• Deployment
  • Nginx
  • HAProxy
• Credits

SockJS-cyclone

SockJS-cyclone is a pure Python server implementation for the SockJS client library running on the Cyclone web server.

SockJS-cyclone is released under the MIT license.

What is SockJS?

SockJS is a browser JavaScript library that provides a WebSocket-like object. SockJS gives you a coherent, cross-browser, JavaScript API which creates a low latency, full duplex, cross-domain communication channel between the browser and the web server, which consistently works across old browsers, misconfigured or old proxies and firewalls, etc. by automatically using other transports as a fallback mechanism.

SockJS main features:

• simple APIs, as close to the WebSocket API as possible;
• scaling and load balancing techniques;
• very fast connection establishment;
• pure JavaScript library on the client-side, no flash needed;
• very extensive code testing available for both the server and client sides.

SockJS-cyclone fully supports the SockJS protocol version 0.3.3.

What is Cyclone?

Cyclone is a very fast and scalable web server framework that implements the Tornado API as a Twisted protocol.

How does it look like?

A live demo deployed on Heroku can be found here.

Here is a small example for an echo server:

from twisted.internet import reactor
import cyclone
import sockjs.cyclone

class EchoConnection(sockjs.cyclone.SockJSConnection):
    def messageReceived(self, message):
        self.sendMessage(message)

if __name__ == "__main__":
    EchoRouter = sockjs.cyclone.SockJSRouter(EchoConnection, '/echo')
    app = cyclone.web.Application(EchoRouter.urls)
    reactor.listenTCP(8888, app)
    reactor.run()

and an excerpt for the client:

var sock = new SockJS('http://mydomain.com/echo');
sock.onopen = function() {
    console.log('open');
};
sock.onmessage = function(e) {
    console.log('message', e.data);
};
sock.onclose = function() {
    console.log('close');
};
sock.send('hello!');

Complete examples can be found here.

Multiplexing

SockJS-Cyclone supports multiplexing (multiple distinct channels over a single shared connection):

from twisted.internet import reactor
import cyclone
from sockjs.cyclone.conn import SockJSConnection, MultiplexConnection
from sockjs.cyclone.router import SockJSRouter

class AnnConnection(SockJSConnection):
    def messageReceived(self, message):
        self.sendMessage('Ann received ' + message)

class BobConnection(SockJSConnection):
    def messageReceived(self, message):
        self.sendMessage('Bob received ' + message)

class CarlConnection(SockJSConnection):
    def messageReceived(self, message):
        self.sendMessage('Carl received ' + message)

if __name__ == "__main__":
    multiplexConnection = MultiplexConnection.create(ann=AnnConnection,
                                                     bob=BobConnection,
                                                     carl=CarlConnection)

    echoRouter = SockJSRouter(multiplexConnection, '/echo')

    app = cyclone.web.Application(echoRouter.urls)
    reactor.listenTCP(8888, app)
    reactor.run()

See the websocket-multiplex library for the client support, and the complete example.

Installation

Install from pypi with:

pip install sockjs-cyclone

or from the latest sources with:

git clone https://github.com/flaviogrossi/sockjs-cyclone.git
cd sockjs-cyclone
python setup.py install

SockJS-cyclone API

The main interaction with SockJS-cyclone happens via the two classes SockJSRouter and SockJSConnection.

SockJSConnection

The SockJSConnection class represent a connection with a client and contains the logic of your application. Its main methods are:

• connectionMade(request): called when the connection with the client is established;
• messageReceived(message): called when a new message is received from the client;
• sendMessage(message): call when you want to send a new message to the client;
• close(): close the connection;
• connectionLost(): called when the connection with the client is lost or explicitly closed.

SockJSRouter

The SockJSRouter class routes the requests to the various connections according to the url prefix. Its main methods are:

• __init__(connection, prefix, user_settings): bounds the given connection to the given url prefix;
• urls: read only property to be used to initialize the cyclone application with all the needed sockjs urls.

Deployment

SockJS servers are usually deployed in production behind reverse proxies and/or load balancers. The most used options are currently Nginx and HAProxy.

For Heroku deployment, see the quickstart instructions here.

Nginx

Two major options are needed to fully support proxying requests to a SockJS-Cyclone server: setting the HTTP protocol version to 1.1 and passing upgrade headers to the server. The relevant portion of the required configuration is:

server {
    listen       80;
    server_name  localhost;

    location / {
        proxy_pass          http://<sockjs_server>:<port>;
        proxy_http_version  1.1;
        proxy_set_header    Upgrade $http_upgrade;
        proxy_set_header    Connection "upgrade";
        proxy_set_header    Host $http_host;
        proxy_set_header    X-Real-IP $remote_addr;
    }

}

For websocket support, nginx version 1.3.13 or above is needed.

A working nginx.conf example can be found in the examples directory.

HAProxy

A complete example for HAProxy deployment and load balancing can be found on SockJS-Node Readme.

Credits

Thanks to:

• Serge S. Koval for the tornado implementation;
• VoiSmart s.r.l for sponsoring the project.