A Brief History of Channels

A talk I gave at DjangoCon Europe 2016

Transcript

1. Andrew Godwin @andrewgodwin
   BRIEF HISTORY
   of
   CHANNELS
   A
   

   View Slide

2. Andrew Godwin
   Hi, I'm
   Django core developer
   Senior Software Engineer at
   Likes networking a little bit too much
   

   View Slide

3. Channels
   

   View Slide

4. Channels?
   

   View Slide

5. WebSocket
   

   View Slide

6. HTTP 1
   request
   response
   Browser Server
   request
   response
   request
   response
   request
   response
   

   View Slide

7. HTTP 2
   request
   response
   Browser Server
   request
   response
   request 1
   response 2
   request 2
   response 1
   

   View Slide

8. WSGI
   request
   response
   Browser Server Django
   call app
   return val
   

   View Slide

9. WebSockets
   receive
   send
   Browser Server
   send
   receive
   send
   send
   

   View Slide

10. receive
    send
    Browser Server
    send
    receive
    send
    send
    Django
    ?
    

    View Slide

11. Hard to deadlock
    Built-in authorisation
    Scales down
    Widely deployable
    Optional
    

    View Slide

12. Django is not built for this.
    

    View Slide

13. But what if it was?
    

    View Slide

14. Instead of requests, we have events
    

    View Slide

15. Events of the same type are grouped
    on a named channel
    

    View Slide

16. HTTP requests
    HTTP responses
    WebSocket connecteds
    WebSocket frames received
    WebSocket frames sent
    WebSocket disconnections
    

    View Slide

17. A channel is a:
    named,
    first-in-first-out,
    at-most-once,
    non-broadcast,
    network-transparent
    queue of messages
    

    View Slide

18. http.request
    Protocol Server Worker Server
    http.response
    websocket.connect
    websocket.send
    websocket.receive
    websocket.send
    websocket.send
    

    View Slide

19. Responses are on single-reader channels
    (http.response!1A2B3C)
    

    View Slide

20. You can send onto channels from
    anywhere
    

    View Slide

21. How do you use it?
    

    View Slide

22. View
    request
    response
    callable
    

    View Slide

23. Consumer
    event
    event
    callable
    event
    event
    

    View Slide

24. Every message on a channel runs
    the consumer function
    

    View Slide

25. http.request routes to a
    view system consumer
    

    View Slide

26. 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,
    })
    

    View Slide

27. routing.py: urls.py for Channels
    

    View Slide

28. message.user: like request.user
    

    View Slide

29. message.channel_session:
    per-socket sessions
    

    View Slide

30. Groups
    broadcast/pub-sub
    

    View Slide

31. Add a channel to a Group
    Remove a channel from a Group
    Send to a Group
    

    View Slide

32. Worked Examples
    github.com/andrewgodwin/channels-examples
    

    View Slide

33. Liveblog
    http.request Django view layer
    websocket.connect Add to liveblog Group
    websocket.disconnect Remove from liveblog Group
    Send notification to liveblog
    

    View Slide

34. 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
    

    View Slide

35. It's so easy to join!
    CALL NOW
    

    View Slide

36. Things I didn't even get to:
    Replacing WSGI
    Pluggable channel backends
    Sharding and scaling
    It's still just runserver
    

    View Slide

37. A base for the future
    Scheduler?
    Retry logic?
    Generic Consumers?
    ...and much more
    

    View Slide

38. 1.10
    "Provisional"?
    

    View Slide

39. 1.8 1.9
    pip install channels
    

    View Slide

40. channels.readthedocs.com
    github.com/andrewgodwin/channels-examples
    

    View Slide

41. Thanks.
    Andrew Godwin
    @andrewgodwin
    

    View Slide