Django and this thing called Channels

Transcript

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   Andrew Godwin @andrewgodwin DJANGO and this thing called CHANNELS

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   Andrew Godwin Hi, I'm Django core developer Senior Software Engineer

   at Likes complaining about networking
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   The Problem First: The Solution Then: The Future Finally:

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   The Problem WSGI ain't so bad

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   Browser HTTP Webserver Django WSGI View Handler

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   Browser WebSocket Webserver Django ???? ??? ????

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   Very hard to deadlock/cause errors Seems "Django-ish" DESIGN GOALS Scales

   decently All works inside runserver
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   Browser WebSocket Webserver Django Channels Consumers Routing

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   Browser HTTP Webserver Django Channels Consumer Ch. Routing View URL

   dispatch
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    The Solution A Series Of Channels

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    An ordered, first-in-first-out, at-most once queue with expiry and delivery

    to only one listening consumer. Identified by a unique unicode name. WHAT IS A CHANNEL?
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    Producers Consumers Channel

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    There are standard channel names: STANDARDS Clients have unique response

    channels: http.request websocket.connect websocket.receive !http.response.jaS4kSDj !websocket.send.Qwek120d
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    There are standard message formats: STANDARDS - HTTP request -

    WebSocket close - HTTP response chunk But you can make your own channel names and formats too.
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    But how do we do this without making Django asynchronous?

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    Channels are network-transparent, and protocol termination is separate from business

    logic process 1 process 2 protocol server worker server channels client socket
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    Async/cooperative code, but none of yours process 1 process 2

    protocol server worker server channels client socket Your logic running synchronously worker server
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    For runserver, we run them as threads thread 1 thread

    2 protocol server worker server channels client socket worker server thread 3 process 1
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    A view receives a request and sends a single response.

    WHAT IS A CONSUMER? A consumer receives a message and sends zero or more messages.
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    EXAMPLE This echoes messages back: def ws_message(message): text = message.content['text']

    reply = "You said: %s" % text message.reply_channel.send({ 'text': reply, })
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    EXAMPLE This notifies clients of new blog posts: def newpost(message):

    for client in client_list: Channel(client).send({ 'text': message.content['id'], })
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    EXAMPLE But Channels has a better solution for that: #

    Channel "websocket.connect" def connect(message): Group('liveblog').add( message.reply_channel) # Channel "new-liveblog" def newpost(message): Group('liveblog').send({ 'text': message.content['id'], })
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    EXAMPLE And you can send to channels from anywhere: class

    LiveblogPost(models.Model): ... def save(self): ... Channel('new-liveblog').send({ 'id': str(self.id), })
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    EXAMPLE You can offload processing from views: def upload_image(request): ...

    Channel('thumbnail').send({ 'id': str(image.id), }) return render(...)
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    EXAMPLE All the routing is set up like URLs: from

    .consumers import ws_connect routing = { 'websocket.connect': ws_connect, 'websocket.receive': 'a.b.receive', 'thumbnail': 'images.consumers.thumb', }
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    EXAMPLE The HTTP channel just goes to the view system

    by default. routing = { # This is actually the default 'http.request': 'channels.asgi.ViewConsumer', }
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    The Future What does it all mean?

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    WSGI

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    WSGI 2?

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    ASGI channels.readthedocs.org/en/latest/asgi.html

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    channel_layer.send(channel, message) channel_layer.receive_many(channels) + message standards + extensions (groups, stats)

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    Daphne HTTP/WebSocket ASGI server asgiref Memory layer, conformance suite, WSGI

    adapters asgi_redis Redis-based channel layer
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    Raw ASGI app example: while True: channel, message = layer.receive_many(

    ["http.request"], block = True, ) if channel is None: continue layer.send( message['reply_channel'], { 'content': 'Hello World!', 'status': 200, } )
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    Django 1.10

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    Django 1.10 And 1.8, 1.9 as a third-party app

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    It's all optional. No need to change anything if you

    don't want to use channels.
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    pip install channels channels.readthedocs.org

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    Thanks. Andrew Godwin @andrewgodwin