Re: Channels 2.0 - Exception when sending a message to client

While I'm at it, would you mind confirming if I understand the following changes in channels 2.0 correctly ?

1) Channel names are not auto-detected and must be specified when running a worker

2) runserver no long starts up a worker by default, this has be done manually

On Sunday, February 25, 2018 at 2:56:45 AM UTC+2, muha...@swordfish.co.za wrote:

I'm still trying to find my way around channels 2.0, so I'm not sure if my implementation is incorrect or if this is a valid issue. I'm going to post as much info as possible in the hope that it will assist with finding the problem.

I have a single page app which opens a JS websocket connection - with channels 1 I used to add a session_key to the querystring and that used to handle the authentication.

I see this is no longer the case, so I now have a custom middleware class that sets the user object on the scope:

from django.contrib.sessions.models import Session

from users.models import User


class QueryAuthMiddleware:

    def __init__(self, inner):
        # Store the ASGI application we were passed
        self.inner = inner

    def __call__(self, scope):
        # Look up user from query string (you should also do things like
        # check it's a valid user ID, or if scope["user"] is already populated)
        if scope.get("user", None) is None:
            session_obj = Session.objects.get(session_key=scope["query_string"].decode("utf-8").split("=")[1])
            session_decoded = session_obj.get_decoded()

            scope["user"] = User.objects.get(id=session_decoded.get("_auth_user_id"))

            # Return the inner application directly and let it run everything else
        return self.inner(scope)

This is in turn added to my routing (channels.py):

from django.conf.urls import url
from django.conf import settings
from channels.routing import ProtocolTypeRouter, URLRouter, ChannelNameRouter

from notifications.consumer import TestWebsocketConsumer, TestConsumer
from notifications.middleware.query_auth_middleware import QueryAuthMiddleware

ROOT_PATH = "" if settings.DEBUG else "/ws/"


application = ProtocolTypeRouter({

    "websocket": QueryAuthMiddleware(
        URLRouter([
            url(f"^{ROOT_PATH}(?P<user_id>[-\w]+)/$", TestWebsocketConsumer),

        ])
    ),

    "channel": ChannelNameRouter({
         "user-notifications": TestConsumer,
    })


})

Here's my consumers.py:

from asgiref.sync import async_to_sync
from channels.consumer import SyncConsumer
from channels.generic.websocket import WebsocketConsumer


class TestWebsocketConsumer(WebsocketConsumer):
    def websocket_connect(self, message):
        async_to_sync(self.channel_layer.group_add)(str(self.scope["user"].id), "user-notifications")
        self.connect()


class TestConsumer(SyncConsumer):
    def notification_handler(self, message):

        self.send(
            {
             "type": "websocket.send",
             "text": message["text"]
            }
        )

The idea of the app is that each user that logs in on the front end is able to receive messages meant only for them sent by the back end.  I have been trying to test it like this:

>>> channel_layer = get_channel_layer()
>>> async_to_sync(channel_layer.send)("user-notifications", {"type": "notification.handler", "text": "My Message"})

Here's the traceback in the runworker output:

2018-02-25 02:34:14,002 - INFO - runworker - Running worker for channels ['user-notifications']

ERROR:root:Exception inside application: You must implement application_send()

  File "/Users/muhammed/projects/xxx/lib/python3.6/site-packages/channels/consumer.py", line 54, in __call__

    await await_many_dispatch([receive, self.channel_receive], self.dispatch)

  File "/Users/muhammed/projects/xxx/lib/python3.6/site-packages/channels/utils.py", line 48, in await_many_dispatch

    await dispatch(result)

  File "/Users/muhammed/projects/xxx/lib/python3.6/site-packages/asgiref/sync.py", line 110, in __call__

    return await asyncio.wait_for(future, timeout=None)

  File "/usr/local/Cellar/python3/3.6.1/Frameworks/Python.framework/Versions/3.6/lib/python3.6/asyncio/tasks.py", line 333, in wait_for

    return (yield from fut)

  File "/usr/local/Cellar/python3/3.6.1/Frameworks/Python.framework/Versions/3.6/lib/python3.6/concurrent/futures/thread.py", line 55, in run

    result = self.fn(*self.args, **self.kwargs)

  File "/Users/muhammed/projects/xxx/lib/python3.6/site-packages/channels/db.py", line 13, in thread_handler

    return super().thread_handler(loop, *args, **kwargs)

  File "/Users/muhammed/projects/xxx/lib/python3.6/site-packages/asgiref/sync.py", line 125, in thread_handler

    return self.func(*args, **kwargs)

  File "/Users/muhammed/projects/xxx/lib/python3.6/site-packages/channels/consumer.py", line 99, in dispatch

    handler(message)

  File "/Users/muhammed/projects/xxx/my-app/app/notifications/consumer.py", line 18, in notification_handler

    "text": message["text"]

  File "/Users/muhammed/projects/xxx/lib/python3.6/site-packages/channels/consumer.py", line 107, in send

    self.base_send(message)

  File "/Users/muhammed/projects/xxx/lib/python3.6/site-packages/asgiref/sync.py", line 64, in __call__

    return call_result.result()

  File "/usr/local/Cellar/python3/3.6.1/Frameworks/Python.framework/Versions/3.6/lib/python3.6/concurrent/futures/_base.py", line 405, in result

    return self.__get_result()

  File "/usr/local/Cellar/python3/3.6.1/Frameworks/Python.framework/Versions/3.6/lib/python3.6/concurrent/futures/_base.py", line 357, in __get_result

    raise self._exception

  File "/Users/muhammed/projects/xxx/lib/python3.6/site-packages/asgiref/sync.py", line 78, in main_wrap

    result = await self.awaitable(*args, **kwargs)

  File "/Users/muhammed/projects/xxx/lib/python3.6/site-packages/asgiref/server.py", line 71, in application_send

    raise NotImplementedError("You must implement application_send()")

  You must implement application_send()

OS: MacOS High Sierra

Python: 3.6.1

Django==2.0.2

channels==2.0.2

channels-redis==2.1.0

asgiref==2.1.6

daphne==2.0.4

Config from settings.py:

# -- Channels Details
CHANNEL_LAYERS = {
    "default": {
        "BACKEND": "channels_redis.core.RedisChannelLayer",
        "CONFIG": {
            "hosts": [("localhost", 6379)]
        }
    }
}

ASGI_APPLICATION = "myapp.settings.channels.application"

Any help would be appreciated.

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