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3.0.0 Release Notes

The Channels 3 update brings Channels into line with Django’s own async ASGI support, introduced with Django 3.0.

Channels now integrates with Django’s async HTTP handling, whilst continuing to support WebSockets and other exciting consumer types.

Channels 3 supports Django 3.x and beyond, as well continuing to support the Django 2.2 LTS. We will support Django 2.2 at least until the Django 3.2 LTS is released, yet may drop support after that, but before Django 2.2 is officially end-of-life.

Likewise, we support Python 3.6+ but we strongly advise you to update to the latest Python versions, so 3.9 at the time of release.

In both our Django and Python support, we reflect the reality that async Python and async Django are still both evolving rapidly. Many issues we see simply disappear if you update. Whatever you are doing with async, you should make sure you’re on the latest versions.

The highlight of this release is the upgrade to ASGI v3, which allows integration with Django’s ASGI support. There are also two additional deprecations that you will need to deal with if you are updating an existing application.

Update to ASGI 3

  • Consumers are now ASGI 3 single-callables with the signature:

    application(scope, receive, send)
    

    For generic consumers this change should be largely transparent, but you will need to update __init__() (no longer taking the scope) and __call__() (now taking the scope) if you implemented these yourself.

  • Consumers now have an as_asgi() class method you need to call when setting up your routing:

    websocket_urlpatterns = [
        re_path(r'ws/chat/(?P<room_name>\w+)/$', consumers.ChatConsumer.as_asgi()),
    ]
    

    This returns an ASGI application that will instantiate the consumer per-request. It’s similar to Django’s as_view(), which serves the same purpose. You can pass in keyword arguments for initialization if your consumer requires them.

  • Middleware will also need to be updated to the ASGI v3 signature. The channels.middleware.BaseMiddleware class is simplified, and available as an example. You probably don’t need to actually subclass it under ASGI 3.

Deprecations

  • Using ProtocolTypeRouter without an explicit "http" key is now deprecated.

    Following Django conventions, your entry point script should be named asgi.py, and you should use Django’s get_asgi_application(), that is used by Django’s default asgi.py template to route the "http" handler:

    from django.core.asgi import get_asgi_application
    
    application = ProtocolTypeRouter({
        "http": get_asgi_application(),
        # Other protocols here.
    })
    

    Once the deprecation is removed, when we drop support for Django 2.2, not specifying an "http" key will mean that your application will not handle HTTP requests.

  • The Channels built-in HTTP protocol AsgiHandler is also deprecated. You should update to Django 3.0 or higher and use Django’s get_asgi_application(). Channel’s AsgiHandler will be removed when we drop support for Django 2.2.

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