Tornadio

Contributors

• Serge S. Koval

Credits

Authors of SocketTornad.IO project:

• Brendan W. McAdams bwmcadams@evilmonkeylabs.com
• Matt Swanson

This is implementation of the Socket.IO realtime transport library on top of the Tornado framework.

Short Background

There's a library which already implements Socket.IO integration using Tornado framework - SocketTornad.IO, but it was not finished, has several known bugs and not very well structured.

TornadIO is different from SocketTornad.IO library in following aspects:

• Simpler internal design, easier to maintain/extend
• No external dependencies (except of the Tornado itself and simplejson on python < 2.6)
• Properly handles on_open/on_close events for polling transports
• Proper Socket.IO protocol parser
• Proper unicode support
• Actively maintained

Introduction

In order to start working with the TornadIO library, you need to know some basic concepts on how Tornado works. If you don't, please read Tornado tutorial, which can be found here.

If you're familiar with Tornado, do following to add support for Socket.IO to your application:

1. Derive from tornadio.SocketConnection class and override on_message method (on_open/on_close are optional):

class MyConnection(tornadio.SocketConnection):
  def on_message(self, message):
    pass

2. Create handler object that will handle all socket.io transport related functionality:

MyRouter = tornadio.get_router(MyConnection)

3. Add your handler routes to the Tornado application:

application = tornado.web.Application(
  [MyRouter.route()],
  socket_io_port = 8000)

4. Start your application
5. You have your socket.io server running at port 8000. Simple, right?

Goodies

SocketConnection class provides three overridable methods:

1. on_open called when new client connection was established.
2. on_message called when message was received from the client. If client sent JSON object, it will be automatically decoded into appropriate Python data structures.
3. on_close called when client connection was closed (due to network error, timeout or just client-side disconnect)

Each SocketConnection has send() method which is used to send data to the client. Input parameter can be one of the:

1. String/unicode string - sent as is (though with utf-8 encoding)
2. Arbitrary python object - encoded as JSON string automatically
3. List of python objects/strings - encoded as series of the socket.io messages using one of the rules above.

Configuration

You can configure your handler by passing settings to the get_router function as a dict object.

• enabled_protocols: This is a list of the socket.io protocols the server will respond requests for. Possibilities are:
• websocket: HTML5 WebSocket transport
• flashsocket: Flash emulated websocket transport. Requires Flash policy server running on port 843.
• xhr-multipart: Works with two connections - long GET connection with multipart transfer encoding to receive updates from the server and separate POST requests to send data from the client.
• xhr-polling: Long polling AJAX request to read data from the server and POST requests to send data to the server. If message is available, it will be sent through open GET connection (which is then closed) or queued on the server otherwise.
• jsonp-polling: Similar to the xhr-polling, but pushes data through the JSONp.
• htmlfile: IE only. Creates HTMLFile control which reads data from the server through one persistent connection. POST requests are used to send data back to the server.
• session_check_interval: Specifies how often TornadIO will check session container for expired session objects. In seconds.
• session_expiry: Specifies session expiration interval, in seconds. For polling transports it is actually maximum time allowed between GET requests to consider virtual connection closed.
• heartbeat_interval: Heartbeat interval for persistent transports. Specifies how often heartbeat events should be sent from the server to the clients.
• xhr_polling_timeout: Timeout for long running XHR connection for xhr-polling transport, in seconds. If no data was available during this time, connection will be closed on server side to avoid client-side timeouts.

Resources

You're not limited with one connection type per server - you can serve different clients in one server instance.

By default, all socket.io clients use same resource - 'socket.io'. You can change resource by passing resource parameter to the get_router function:

ChatRouter = tornadio.get_router(MyConnection, resource='chat')

In the client, provide resource you're connecting to, by passing resource parameter to io.Socket constructor:

sock = new io.Socket(window.location.hostname, {
             port: 8001,
             resource: 'chat',
           });

As it was said before, you can have as many connection types as you want by having unique resources for each connection type:

ChatRouter = tornadio.get_router(ChatConnection, resource='chat')
PingRouter = tornadio.get_router(PingConnection, resource='ping')
MapRouter = tornadio.get_router(MapConnection, resource='map')

application = tornado.web.Application(
  [ChatRouter.route(), PingRouter.route(), MapRouter.route()],
  socket_io_port = 8000)

Extra parameters

If you need some kind of user authentication in your application, you have two choices:

1. Send authentication token as a first message from the client
2. Provide authentication token as part of the resource parameter

TornadIO has support for extra data passed through the socket.io resources.

You can provide regexp in extra_re parameter of the get_router function and matched data can be accessed in your on_open handler as kwargs['extra']. For example:

class MyConnection(tornadio.SocketConnection):
  def on_open(self, *args, **kwargs):
    print 'Extra: %s' % kwargs['extra']

ChatRouter = tornadio.get_router(MyConnection, resource='chat', extra_re='\d+', extra_sep='/')

and on the client-side:

sock = new io.Socket(window.location.hostname, {
             port: 8001,
             resource: 'chat/123',
           });

If you will run this example and connect with sample client, you should see 'Extra: 123' printed out.

Starting Up

Best Way: SocketServer

We provide customized version (shamelessly borrowed from the SocketTornad.IO library) of the HttpServer, which simplifies start of your TornadIO server.

To start it, do following (assuming you created application object before):

if __name__ == "__main__":
  socketio_server = SocketServer(application)

SocketServer will automatically start Flash policy server, if required.

Going big

So, you've finished writting your application and want to share it with rest of the world, so you started thinking about scalability, deployment options, etc.

Most of the Tornado servers are deployed behind the nginx, which also used to serve static content. This won't work very well with TornadIO, as nginx does not support HTTP/1.1, does not support websockets and XHR-Multipart transport just won't work.

So, to load balance your TornadIO instances, use alternative solutions like HAProxy. However, HAProxy does not work on Windows, so if you plan to deploy your solution on Windows platform, you might want to take look into MLB.

Scalability is completely different beast. It is up for you, as a developer, to design scalable architecture of the application.

For example, if you need to have one large virtual server out of your multiple physical processes (or even servers), you have to come up with some kind of the synchronization mechanism. This can be either common meeting point (and also point of failure), like memcached, redis, etc. Or you might want to use some transporting mechanism to communicate between servers, for example something AMQP based, ZeroMQ or just plain sockets with your protocol.

For example, with message queues, you can treat TornadIO as a message gateway between your clients and your server backend(s).

Examples

Chatroom Example

There is a chatroom example application from the SocketTornad.IO library, contributed by swanson. It is in the examples/chatroom directory.

Ping Example

Simple ping/pong example to measure network performance. It is in the examples/ping directory.

Transports Example

Simple ping/pong example with chat-like interface with selectable transports. It is in the examples/transports directory.