De-duplicate duplicate handling

move the "duplicate state event" handling down into `handle_new_client_event`
where it can be shared between multiple call paths.

synapse/handlers/message.py

@@ -674,22 +674,14 @@ class EventCreationHandler:
 
         assert self.hs.is_mine(user), "User must be our own: %s" % (user,)
 
-        if event.is_state():
-            prev_event = await self.deduplicate_state_event(event, context)
-            if prev_event is not None:
-                logger.info(
-                    "Not bothering to persist state event %s duplicated by %s",
-                    event.event_id,
-                    prev_event.event_id,
-                )
-                # we know it was persisted, so must have a stream ordering
-                assert prev_event.internal_metadata.stream_ordering
-                return prev_event.internal_metadata.stream_ordering
-
-        return await self.handle_new_client_event(
+        ev = await self.handle_new_client_event(
             requester=requester, event=event, context=context, ratelimit=ratelimit
         )
 
+        # we know it was persisted, so must have a stream ordering
+        assert ev.internal_metadata.stream_ordering
+        return ev.internal_metadata.stream_ordering
+
     async def deduplicate_state_event(
         self, event: EventBase, context: EventContext
     ) -> Optional[EventBase]:
@@ -845,8 +837,10 @@ class EventCreationHandler:
         context: EventContext,
         ratelimit: bool = True,
         extra_users: List[UserID] = [],
-    ) -> int:
-        """Processes a new event. This includes checking auth, persisting it,
+    ) -> EventBase:
+        """Processes a new event.
+
+        This includes deduplicating, checking auth, persisting,
         notifying users, sending to remote servers, etc.
 
         If called from a worker will hit out to the master process for final
@@ -860,9 +854,20 @@ class EventCreationHandler:
             extra_users: Any extra users to notify about event
 
         Return:
-            The stream_id of the persisted event.
+            If the event was deduplicated, the previous, duplicate, event. Otherwise,
+            `event`.
         """
 
+        if event.is_state():
+            prev_event = await self.deduplicate_state_event(event, context)
+            if prev_event is not None:
+                logger.info(
+                    "Not bothering to persist state event %s duplicated by %s",
+                    event.event_id,
+                    prev_event.event_id,
+                )
+                return prev_event
+
         if event.is_state() and (event.type, event.state_key) == (
             EventTypes.Create,
             "",
@@ -917,13 +922,13 @@ class EventCreationHandler:
                 )
                 stream_id = result["stream_id"]
                 event.internal_metadata.stream_ordering = stream_id
-                return stream_id
+                return event
 
             stream_id = await self.persist_and_notify_client_event(
                 requester, event, context, ratelimit=ratelimit, extra_users=extra_users
             )
 
-            return stream_id
+            return event
         except Exception:
             # Ensure that we actually remove the entries in the push actions
             # staging area, if we calculated them.

synapse/handlers/room_member.py

@@ -188,16 +188,6 @@ class RoomMemberHandler(metaclass=abc.ABCMeta):
             require_consent=require_consent,
         )
 
-        # Check if this event matches the previous membership event for the user.
-        duplicate = await self.event_creation_handler.deduplicate_state_event(
-            event, context
-        )
-        if duplicate is not None:
-            # Discard the new event since this membership change is a no-op.
-            # we know it was persisted, so must have a stream ordering.
-            assert duplicate.internal_metadata.stream_ordering
-            return duplicate.event_id, duplicate.internal_metadata.stream_ordering
-
         prev_state_ids = await context.get_prev_state_ids()
 
         prev_member_event_id = prev_state_ids.get((EventTypes.Member, user_id), None)
@@ -222,7 +212,7 @@ class RoomMemberHandler(metaclass=abc.ABCMeta):
                         retry_after_ms=int(1000 * (time_allowed - time_now_s))
                     )
 
-        stream_id = await self.event_creation_handler.handle_new_client_event(
+        result_event = await self.event_creation_handler.handle_new_client_event(
             requester, event, context, extra_users=[target], ratelimit=ratelimit,
         )
 
@@ -232,7 +222,9 @@ class RoomMemberHandler(metaclass=abc.ABCMeta):
                 if prev_member_event.membership == Membership.JOIN:
                     await self._user_left_room(target, room_id)
 
-        return event.event_id, stream_id
+        # we know it was persisted, so should have a stream ordering
+        assert result_event.internal_metadata.stream_ordering
+        return result_event.event_id, result_event.internal_metadata.stream_ordering
 
     async def copy_room_tags_and_direct_to_room(
         self, old_room_id, new_room_id, user_id
@@ -673,12 +665,6 @@ class RoomMemberHandler(metaclass=abc.ABCMeta):
         else:
             requester = types.create_requester(target_user)
 
-        prev_event = await self.event_creation_handler.deduplicate_state_event(
-            event, context
-        )
-        if prev_event is not None:
-            return
-
         prev_state_ids = await context.get_prev_state_ids()
         if event.membership == Membership.JOIN:
             if requester.is_guest:
@@ -1186,10 +1172,13 @@ class RoomMemberMasterHandler(RoomMemberHandler):
 
         context = await self.state_handler.compute_event_context(event)
         context.app_service = requester.app_service
-        stream_id = await self.event_creation_handler.handle_new_client_event(
+        result_event = await self.event_creation_handler.handle_new_client_event(
             requester, event, context, extra_users=[UserID.from_string(target_user)],
         )
-        return event.event_id, stream_id
+        # we know it was persisted, so must have a stream ordering
+        assert result_event.internal_metadata.stream_ordering
+
+        return result_event.event_id, result_event.internal_metadata.stream_ordering
 
     async def _user_left_room(self, target: UserID, room_id: str) -> None:
         """Implements RoomMemberHandler._user_left_room