Fix workers support when using Redis PubSub layer (#298)

* Fix workers support when using Redis PubSub layer

The new Redis PubSub layer broke support for Channels workers. Add
support for workers by subscribing to non-owned channels instead of
throwing an exception.

Co-authored-by: Carlton Gibson <[email protected]>

channels_redis/pubsub.py

@@ -138,6 +138,11 @@ def _get_group_channel_name(self, group):
         """
         return f"{self.prefix}__group__{group}"
 
+    async def _subscribe_to_channel(self, channel):
+        self.channels[channel] = asyncio.Queue()
+        shard = self._get_shard(channel)
+        await shard.subscribe(channel)
+
     extensions = ["groups", "flush"]
 
     ################################################################################
@@ -157,9 +162,7 @@ async def new_channel(self, prefix="specific."):
         process as a specific channel.
         """
         channel = f"{self.prefix}{prefix}{uuid.uuid4().hex}"
-        self.channels[channel] = asyncio.Queue()
-        shard = self._get_shard(channel)
-        await shard.subscribe(channel)
+        await self._subscribe_to_channel(channel)
         return channel
 
     async def receive(self, channel):
@@ -169,9 +172,7 @@ async def receive(self, channel):
         of the waiting coroutines will get the result.
         """
         if channel not in self.channels:
-            raise RuntimeError(
-                'You should only call receive() on channels that you "own" and that were created with `new_channel()`.'
-            )
+            await self._subscribe_to_channel(channel)
 
         q = self.channels[channel]
 

tests/test_pubsub.py

@@ -24,6 +24,17 @@ async def channel_layer():
     await channel_layer.flush()
 
 
+@pytest.fixture()
+@async_generator
+async def other_channel_layer():
+    """
+    Channel layer fixture that flushes automatically.
+    """
+    channel_layer = RedisPubSubChannelLayer(hosts=TEST_HOSTS)
+    await yield_(channel_layer)
+    await channel_layer.flush()
+
+
 @pytest.mark.asyncio
 async def test_send_receive(channel_layer):
     """
@@ -118,6 +129,30 @@ async def test_groups_same_prefix(channel_layer):
         assert (await channel_layer.receive(channel_name3))["type"] == "message.1"
 
 
+@pytest.mark.asyncio
+async def test_receive_on_non_owned_general_channel(channel_layer, other_channel_layer):
+    """
+    Tests receive with general channel that is not owned by the layer
+    """
+    receive_started = asyncio.Event()
+
+    async def receive():
+        receive_started.set()
+        return await other_channel_layer.receive("test-channel")
+
+    receive_task = asyncio.create_task(receive())
+    await receive_started.wait()
+    await asyncio.sleep(0.1)  # Need to give time for "receive" to subscribe
+    await channel_layer.send("test-channel", "message.1")
+
+    try:
+        # Make sure we get the message on the channels that were in
+        async with async_timeout.timeout(1):
+            assert await receive_task == "message.1"
+    finally:
+        receive_task.cancel()
+
+
 @pytest.mark.asyncio
 async def test_random_reset__channel_name(channel_layer):
     """