Gevent-socketio documentation¶
Introduction¶
Socket.IO is a WebSocket-like abstraction that enables real-time
communication between a browser and a server. gevent-socketio is a
Python implementation of the protocol.
The reference server implementation of Socket.IO runs on Node.js and was
developed by LearnBoost. There are now server implementations in a
variety of languages.
One aim of this project is to provide a single gevent-based
API that works across the different WSGI-based web frameworks out
there (Pyramid, Pylons, Flask, web2py, Django, etc...). Only ~3 lines
of code are required to tie-in gevent-socketio in your framework.
Note: you need to use the gevent python WSGI server to use
gevent-socketio.
Namespaces: since you mostly have one websocket/socket.io
endpoint per website, it is important to be able to namespace the
different real-time activities of the different pages or parts of
your site, just like you need routes to map URLs to different parts
of your code. The Socket.IO 0.7+ namespaces are a welcome addition,
and if you don’t use Socket.IO, you’ll probably end-up writing your
own namespacing mechanism at some point.
Named events: To distinguish the messages that are coming and
going, you most probably want to give them some name. Here again, not
using Socket.IO, you will find yourself implementing a way to tag your
packets with names representing different tasks or actions to
perform. With Socket.IO 0.6 or with normal WebSockets, you would
probably encode a JSON object with one of the keys that is reserved
for that (I used {"type": "submit_something"}. Socket.IO 0.7+
implements named events, which put that information in a terse form on
the wire. It also allows you to define callbacks, that can be
acknowledged by the other endpoint, and then fire back your function
with some return parameters. Something great for RPC, that you’d need
to implement yourself the moment you need it.
Transports: One of the main feature of Socket.IO is the
abstraction of the transport, that gives you real-time web support
down to Internet Explorer 6.0, using long-polling methods. It will
also use native WebSockets when available to the browser, for even
lower latencies.
This implementation covers nearly all the features of the Socket.IO
0.7+ (up to at least 0.9.1) protocol, with events, callbacks. It adds
security in a pythonic way with granular ACLs (which don’t exist in
the Node.js version) at the method level. The project has several
examples in the source code and in the documentation. Any addition
and fixes to the docs are warmly welcomed.
Concepts¶
In order to understand the following documentation articles, let’s
clarify some of the terms used:
A Namespace is like a controller in the MVC world. It encompasses
a set of methods that are logically in it. For example, the
send_private_message event would be in the /chat namespace, as
well as the kick_ban event. Whereas the scan_files event
would be in the /filesystem namespace. Each namespace is
represented by a sub-class of BaseNamespace. A simple
example would be, on the client side (the browser):
var socket = io.connect("/chat");
having loaded the socket.io.js library somewhere in your <head>.
On the server (this is a Pyramid example, but its pretty much the same
for other frameworks):
from socketio.namespace import BaseNamespace
class ChatNamespace(BaseNamespace):
def on_chat(self, msg):
self.emit('chat', msg)
def socketio_service(request):
socketio_manage(request.environ, {'/chat': ChatNamespace},
request)
return "out"
Here we use socketio.socketio_manage() to start the Socket.IO
machine, and handle the real-time communication.
You will come across the notion of a Socket. This is a virtual
socket, that abstracts the fact that some transports are long-polling
and others are stateful (like a Websocket), and exposes the same
functionality for all. You can have many namespaces inside a Socket,
each delimited by their name like /chat, /filesystem or
/foobar. Note also that there is a global namespace, identified
by an empty string. Some times, the global namespace has special
features, for backwards compatibilty reasons (we only have a global
namespace in version 0.6 of the protocol). For example, disconnecting
the global namespace means disconnect the full socket. Disconnecting
a qualified namespace, on the other hand, only removes access to that
namespace.
The Socket is responsible from taking the packets, which are, in
the realm of a Namespace or a Socket object, a dictionary that
looks like:
{"type": "event",
"name": "launch_superhero",
"args": ["Superman", 123, "km", {"hair_color": "brown"}]}
These packets are serialized in a compact form when its time to put
them on the wire. Socket.IO also has some optimizations if we need to
send many packets on some long-polling transports.
At this point, if you don’t know gevent, you probably will want to
learn a bit more about it, since it is the base you will be working
on:
http://www.gevent.org/
Getting started¶
Until we have a fully-fledged tutorial, please check out our example
applications and the API documentation.
See this doc for different servers integration:
Server integration layers
Examples¶
The gevent-socketio holds several examples:
https://github.com/abourget/gevent-socketio/tree/master/examples
chat.py is a bare-bone WSGI app with a minimal socketio integration
chatter2 is a simple chat application, showing off the minimal setup
chatter3 is an app using socket.io, backbone.js and redis for pubsub
chatter4 is chatter3 with persistence added.
- testapp is the app we use to test the different features, so there
are a couple of more advanced use-cases demonstrated there
pyvore is an application that was developed to serve as real-time
chat in conferences like the PyCon:
https://github.com/sontek/pyvore
This app is a Django tic-tac-toe application that uses the latest
gevent-socketio:
https://github.com/sontek/django-tictactoe
API docs¶
https://github.com/abourget/gevent-socketio/tree/master/examples
-
chat.py is a bare-bone WSGI app with a minimal socketio integration
-
chatter2 is a simple chat application, showing off the minimal setup
-
chatter3 is an app using socket.io, backbone.js and redis for pubsub
-
chatter4 is chatter3 with persistence added.
-
- testapp is the app we use to test the different features, so there
-
are a couple of more advanced use-cases demonstrated there