Catch AttributeErrors when calling registerProducer

changelog.d/10995.bugfix

@@ -0,0 +1 @@
+Correct a bugfix introduced in Synapse v1.44.0 that wouldn't catch every error of the connection breaks before a response could be written to it.

synapse/http/server.py

@@ -563,7 +563,11 @@ def __init__(
 
         try:
             self._request.registerProducer(self, True)
-        except RuntimeError as e:
+        except (AttributeError, RuntimeError) as e:
+            # Twisted will raise a RuntimeError in some cases.
+            # Calling self._request.registerProducer might also raise an AttributeError
+            # since the underlying Twisted code calls self._request.channel.registerProducer,
+            # however self._request.channel will be None if the connection was lost.
             logger.info("Connection disconnected before response was written: %r", e)
 
             # We drop our references to data we'll not use.