Django Channels

Andy Dai

andydai@gliacloud.com

Django awarded MOSS Grant

We've been awarded $150,000 to help fund the development of Channels, the initiative to rewrite the

core of Django to support (among other things) WebSockets and background tasks, and to integrate

key parts of the Django REST Framework request/response code into Django, such as content

negotiation.

Andrew Godwin

Concept of Channels

What is Channel

• First-in first-out queue

• At-Most-Once delivery

How to use Channels?

def my_consumer(message): pass

channel_routing = { "some-channel": "myapp.consumers.my_consumer", }

Consumer function

Assign a channel to it in the channel routing

Three separate layers

• Interface servers

• The channel backend

• The Workers

def my_consumer(message): Channel( message.reply_channel ).send(HttpResponse(“ok”))

channel_routing = { "http.request": "myapp.consumers.my_consumer", }

Groups

Channels can’t do broadcast

redis_conn = redis.Redis("localhost", 6379)

@receiver(post_save, sender=BlogUpdate) def send_update(sender, instance, **kwargs): # Loop through all response channels and send the update for reply_channel in redis_conn.smembers("readers"): Channel(reply_channel).send( id=instance.id, content=instance.content, )

# Connected to websocket.connect def ws_connect(message): # Add to reader set redis_conn.sadd("readers", message.reply_channel.name)

With Groups

@receiver(post_save, sender=BlogUpdate) def send_update(sender, instance, **kwargs): Group("readers").send( id=instance.id, content=instance.content, )

# Connected to websocket.connect and websocket.keepalive def ws_connect(message): # Add to reader group Group("readers").add(message.reply_channel)

Let’s build a simple chat room

pip install channels

INSTALLED_APPS = ( 'django.contrib.admin', 'django.contrib.auth', 'django.contrib.contenttypes', 'django.contrib.sessions', 'django.contrib.messages', 'django.contrib.staticfiles', 'channels', )

Add ‘channels’

CHANNEL_BACKENDS = { "default": { "BACKEND": "channels.backends.redis_py.RedisChannelBackend", "ROUTING": { "websocket.connect": "chatroom.consumers.ws_add", "websocket.keepalive": "chatroom.consumers.ws_add", "websocket.receive": "chatroom.consumers.ws_message", "websocket.disconnect": "chatroom.consumers.ws_disconnect", }, }, }

CHANNEL_BACKENDS

16

from channels import Group

# Connected to websocket.connect and websocket.keepalive def ws_add(message): Group("chat").add(message.reply_channel)

# Connected to websocket.receive def ws_message(message): Group("chat").send(message.content)

# Connected to websocket.disconnect def ws_disconnect(message): Group("chat").discard(message.reply_channel)

consumers.py

pip install autobahn[twisted] python manage.py runwsserver

Run WebSocket server

socket = new WebSocket("ws://127.0.0.1:9000/");

socket.onmessage = function(e) { $('body').append(e.data+'<br>'); }

Added Some javascript

Persisting Datafrom channels.decorators import channel_session

@channel_session def ws_add(message): room = message.content.get('path').strip('/') message.channel_session['room'] = room print "Room: {room} - ws_add".format(room=room) Group("chat-%s" % room).add( message.reply_channel )

@channel_session def ws_keepalive(message): room = message.channel_session['room'] Group("chat-%s" % room).add( message.reply_channel )

Linearization

The linearize decorator. Any handler decorated with this will use locking to ensure it does not run at the same time as

any other view with linearize on messages with the same reply channel.

@linearize @channel_session def ws_add(message): room = message.content.get('path').strip('/') message.channel_session['room'] = room print "Room: {room} - ws_add".format(room=room) Group("chat-%s" % room).add( message.reply_channel )

@linearize @channel_session def ws_message(message): Group("chat-%s" % message.channel_session['room']).send( content=message.content )

Authenticationfrom channels.auth import ( http_session_user, channel_session_user, transfer_user )

@channel_session @http_session_user def ws_add(message): # Copy user from HTTP to channel session transfer_user(message.http_session, message.channel_session) # Add them to the right group Group( "chat-%s" % message.user.username[0] ).add(message.reply_channel)

@channel_session_user def ws_keepalive(message): # Keep them in the right group Group( "chat-%s" % message.user.username[0] ).add(message.reply_channel)

DEMO

https://github.com/daikeren/channel-example

Some Thoughts

• Channels will become a built-in feature for Django 1.10

• Not stable yet

• Documentation…

• Read the source code!

Q&A