django-websocket

IMPORTANT: Please read the disclaimer a few sections below before you start using django-websocket.

The django-websocket module provides an implementation of the WebSocket Protocol for django. It handles all the low-level details like establishing the connection through sending handshake reply, parsing messages from the browser etc...

It integrates well into django since it provides easy hooks to receive WebSocket requests either for single views through decorators or for the whole site through a custom middleware.

Usage

You can use the accept_websocket decorator if you want to handle websocket connections just for a single view - it will route standard HTTP requests to the view as well. Use require_websocket to only allow WebSocket connections but reject normal HTTP requests.

You can use a middleware if you want to have WebSockets available for all URLs in your application. Add django_websocket.middleware.WebSocketMiddleware to your MIDDLEWARE_CLASSES setting. This will still reject websockets for normal views. You have to set the accept_websocket attribute on a view to allow websockets.

To allow websockets for every single view, set the WEBSOCKET_ACCEPT_ALL setting to True.

The request objects passed to a view, decorated with accept_websocket or require_websocket will have the following attributes/methods attached. These attributes are always available if you use the middleware.

request.is_websocket()

Returns either True if the request has a valid websocket or False if its a normal HTTP request. Use this method in views that can accept both types of requests to distinguish between them.

request.websocket

After a websocket is established, the request will have a websocket attribute which provides a simple API to communicate with the client. This attribute will be None if request.is_websocket() returns False.

It has the following public methods:

WebSocket.wait()

This will return exactly one message sent by the client. It will not return before a message is received or the conection is closed by the client. In this case the method will return None.

WebSocket.read()

The read method will return either a new message if available or None if no new message was received from the client. It is a non-blocking alternative to the wait() method.

WebSocket.count_messages()

Returns the number of queued messages.

WebSocket.has_messages()

Returns True if new messages are available, else False.

WebSocket.send(message)

This will send a single message to the client.

WebSocket.__iter__()

You can use the websocket as iterator. It will yield every new message sent by the client and stop iteration after the client has closed the connection.

Error handling

The library will return a Http 400 error (Bad Request) if the client requests a WebSocket connection, but the request is malformed or not supported by django-websocket.

Examples

Receive one message from the client, send that message back to the client and close the connection (by returning from the view):

from django_websocket import require_websocket

@require_websocket
def echo_once(request):
    message = request.websocket.wait()
    request.websocket.send(message)

Send websocket messages from the client as lowercase and provide same functionallity for normal GET requests:

from django.http import HttpResponse
from django_websocket import accept_websocket

def modify_message(message):
    return message.lower()

@accept_websocket
def lower_case(request):
    if not request.is_websocket():
        message = request.GET['message']
        message = modify_message(message)
        return HttpResponse(message)
    else:
        for message in request.websocket:
            message = modify_message(message)
            request.websocket.send(message)

Disclaimer (what you should know when using django-websocket)

BIG FAT DISCLAIMER - right at the moment its technically NOT possible in any way to use a websocket with WSGI. This is a known issue but cannot be worked around in a clean way due to some design decision that were made while the WSGI stadard was written. At this time things like Websockets etc. didn't exist and were not predictable.

However there are thoughts to extend the WSGI standard to make Websockets possible. Read here for a discussion on the Paste Users mailing list.

But not only WSGI is the limiting factor. Django itself was designed around a simple request to response scenario without Websockets in mind. This also means that providing a standard conform websocket implemention is not possible right now for django. However it works somehow in a not-so pretty way. So be aware that tcp sockets might get tortured while using django-websocket.

Using in production

Be aware that django-websocket is just a toy for its author to play around with at the moment. It is not recommended to use in production without knowing what you do. There are no real tests made in the wild yet.

But this doesn't mean that the project won't grow up in the future. There will be fixes to reported bugs and feature request are welcome to improve the API.

Please write me an email or contact me somewhere else if you have experience with django-websocket in a real project or even in a production environment.

Contribute

Every contribution in any form is welcome. Ask questions, report bugs, request new features, make rants or tell me any other critique you may have.

One of the biggest contributions you can make is giving me a quick Thank you if you like this library or if it has saved you a bunch of time.

But if you want to get your hands dirty:

• Get the code from github: https://github.com/gregmuellegger/django-websocket
• Run tests with python setup.py test.
• Start coding :)
• Send me a pull request or an email with a patch.

Authors

• Gregor Müllegger <gregor@muellegger.de> (http://gremu.net/)

Credits

Some low-level code for WebSocket implementation is borrowed from the eventlet library.