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A Brief History of Channels
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Andrew Godwin
March 31, 2016
Programming
2
2.2k
A Brief History of Channels
A talk I gave at DjangoCon Europe 2016
Andrew Godwin
March 31, 2016
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Transcript
Andrew Godwin @andrewgodwin BRIEF HISTORY of CHANNELS A
Andrew Godwin Hi, I'm Django core developer Senior Software Engineer
at Likes networking a little bit too much
Channels
Channels?
WebSocket
HTTP 1 request response Browser Server request response request response
request response
HTTP 2 request response Browser Server request response request 1
response 2 request 2 response 1
WSGI request response Browser Server Django call app return val
WebSockets receive send Browser Server send receive send send
receive send Browser Server send receive send send Django ?
Hard to deadlock Built-in authorisation Scales down Widely deployable Optional
Django is not built for this.
But what if it was?
Instead of requests, we have events
Events of the same type are grouped on a named
channel
HTTP requests HTTP responses WebSocket connecteds WebSocket frames received WebSocket
frames sent WebSocket disconnections
A channel is a: named, first-in-first-out, at-most-once, non-broadcast, network-transparent queue
of messages
http.request Protocol Server Worker Server http.response websocket.connect websocket.send websocket.receive websocket.send
websocket.send
Responses are on single-reader channels (http.response!1A2B3C)
You can send onto channels from anywhere
How do you use it?
View request response callable
Consumer event event callable event event
Every message on a channel runs the consumer function
http.request routes to a view system consumer
def ws_message(message): # Get things from message data = json.loads(message['text'])
# Use ORM like normal MyModel.objects.create( value=data['value'], ) # Send a reply and close socket message.reply_channel.send({ 'text': 'OK', 'close': True, })
routing.py: urls.py for Channels
message.user: like request.user
message.channel_session: per-socket sessions
Groups broadcast/pub-sub
Add a channel to a Group Remove a channel from
a Group Send to a Group
Worked Examples github.com/andrewgodwin/channels-examples
Liveblog http.request Django view layer websocket.connect Add to liveblog Group
websocket.disconnect Remove from liveblog Group <Article.save> Send notification to liveblog
Chat http.request Django view layer websocket.receive Either add to room
Group or send to chat_messages websocket.disconnect Remove from room Groups chat_messages Send to room Groups
It's so easy to join! CALL NOW
Things I didn't even get to: Replacing WSGI Pluggable channel
backends Sharding and scaling It's still just runserver
A base for the future Scheduler? Retry logic? Generic Consumers?
...and much more
1.10 "Provisional"?
1.8 1.9 pip install channels
channels.readthedocs.com github.com/andrewgodwin/channels-examples
Thanks. Andrew Godwin @andrewgodwin