Fix iscoroutine check for pubsub proxied methods (django#297)

* Fix iscoroutine check for pubsub proxied methods

Adjust the proxying approach in `RedisPubSubChannelLayer` to ensure the
proxied methods are properly marked as coroutines according to
`inspect.iscoroutinefunction`. This can be issue during testing when
trying to mock channel layer methods.

The underlying issue is a [Python bug][1] where partial methods are not
fully unwrapped to determine if they are coroutines. The workaround
simply moves the proxy wrapper to a top-level async function, tricking
`inspect.iscoroutinefunction` to correctly detecting the proxied async
methods.

[1]: https://bugs.python.org/issue38364

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

Author: 2 people

channels_redis/pubsub.py

@@ -34,6 +34,13 @@ def _wrapper(self, *args, **kwargs):
     loop.close = types.MethodType(_wrapper, loop)
 
 
+async def _async_proxy(obj, name, *args, **kwargs):
+    # Must be defined as a function and not a method due to
+    # https://bugs.python.org/issue38364
+    layer = obj._get_layer()
+    return await getattr(layer, name)(*args, **kwargs)
+
+
 class RedisPubSubChannelLayer:
     def __init__(self, *args, **kwargs) -> None:
         self._args = args
@@ -50,7 +57,7 @@ def __getattr__(self, name):
             "group_send",
             "flush",
         ):
-            return functools.partial(self._proxy, name)
+            return functools.partial(_async_proxy, self, name)
         else:
             return getattr(self._get_layer(), name)
 
@@ -82,13 +89,6 @@ def _get_layer(self):
 
         return layer
 
-    def _proxy(self, name, *args, **kwargs):
-        async def coro():
-            layer = self._get_layer()
-            return await getattr(layer, name)(*args, **kwargs)
-
-        return coro()
-
 
 class RedisPubSubLoopLayer:
     """

tests/test_pubsub.py

@@ -1,5 +1,7 @@
 import asyncio
+import inspect
 import random
+import sys
 
 import async_timeout
 import pytest
@@ -164,3 +166,11 @@ def test_multi_event_loop_garbage_collection(channel_layer):
     assert len(channel_layer._layers.values()) == 0
     async_to_sync(test_send_receive)(channel_layer)
     assert len(channel_layer._layers.values()) == 0
+
+
+@pytest.mark.asyncio
+async def test_proxied_methods_coroutine_check(channel_layer):
+    # inspect.iscoroutinefunction does not work for partial functions
+    # below Python 3.8.
+    if sys.version_info >= (3, 8):
+        assert inspect.iscoroutinefunction(channel_layer.send)