Move call invite filtering logic to filter_events_for_client (#17782)

Author: anoadragon453

changelog.d/17782.misc

@@ -0,0 +1 @@
+Improve event filtering for Simplified Sliding Sync.

synapse/handlers/sliding_sync/__init__.py

@@ -761,8 +761,6 @@ async def get_room_sync_data(
                 != Membership.JOIN,
                 filter_send_to_client=True,
             )
-            # TODO: Filter out `EventTypes.CallInvite` in public rooms,
-            # see https://github.com/element-hq/synapse/issues/17359
 
             # TODO: Handle timeline gaps (`get_timeline_gaps()`)
 

synapse/handlers/sync.py

@@ -36,7 +36,6 @@
     Direction,
     EventContentFields,
     EventTypes,
-    JoinRules,
     Membership,
 )
 from synapse.api.filtering import FilterCollection
@@ -790,22 +789,13 @@ async def _load_filtered_recents(
                         )
                     )
 
-                filtered_recents = await filter_events_for_client(
+                loaded_recents = await filter_events_for_client(
                     self._storage_controllers,
                     sync_config.user.to_string(),
                     loaded_recents,
                     always_include_ids=current_state_ids,
                 )
 
-                loaded_recents = []
-                for event in filtered_recents:
-                    if event.type == EventTypes.CallInvite:
-                        room_info = await self.store.get_room_with_stats(event.room_id)
-                        assert room_info is not None
-                        if room_info.join_rules == JoinRules.PUBLIC:
-                            continue
-                    loaded_recents.append(event)
-
                 log_kv({"loaded_recents_after_client_filtering": len(loaded_recents)})
 
                 loaded_recents.extend(recents)

synapse/visibility.py

@@ -33,6 +33,7 @@
     EventTypes,
     EventUnsignedContentFields,
     HistoryVisibility,
+    JoinRules,
     Membership,
 )
 from synapse.events import EventBase
@@ -111,7 +112,17 @@ async def filter_events_for_client(
     # happen within the function.
     events_before_filtering = events.copy()
     # Default case is to *exclude* soft-failed events
-    events = [e for e in events if not e.internal_metadata.is_soft_failed()]
+    events = []
+    found_call_invite = False
+    for event in events_before_filtering:
+        if event.internal_metadata.is_soft_failed():
+            continue
+
+        if event.type == EventTypes.CallInvite and not event.is_state():
+            found_call_invite = True
+
+        events.append(event)
+
     client_config = await storage.main.get_admin_client_config_for_user(user_id)
     if filter_send_to_client and await storage.main.is_server_admin(user_id):
         if client_config.return_soft_failed_events:
@@ -139,7 +150,11 @@ async def filter_events_for_client(
                 [event.event_id for event in events],
             )
 
-    types = (_HISTORY_VIS_KEY, (EventTypes.Member, user_id))
+    types = [_HISTORY_VIS_KEY, (EventTypes.Member, user_id)]
+    if found_call_invite:
+        # We need to fetch the room's join rules state to determine
+        # whether to allow call invites in public rooms.
+        types.append((EventTypes.JoinRules, ""))
 
     # we exclude outliers at this point, and then handle them separately later
     event_id_to_state = await storage.state.get_state_for_events(
@@ -178,6 +193,25 @@ def allowed(event: EventBase) -> EventBase | None:
         if filtered is None:
             return None
 
+        # Filter out call invites in public rooms, as this would potentially
+        # ring a lot of users.
+        if event.type == EventTypes.CallInvite and not event.is_state():
+            # `state_after_event` should only be None if the event is an outlier,
+            # and earlier code should filter out outliers entirely.
+            #
+            # In addition, we only create outliers locally for out-of-band
+            # invite rejections, invites received over federation, or state
+            # events needed to authorise other events. None of this applies to
+            # call invites.
+            assert state_after_event is not None
+
+            room_join_rules = state_after_event.get((EventTypes.JoinRules, ""))
+            if (
+                room_join_rules is not None
+                and room_join_rules.content.get("join_rule") == JoinRules.PUBLIC
+            ):
+                return None
+
         # Annotate the event with the user's membership after the event.
         #
         # Normally we just look in `state_after_event`, but if the event is an outlier