Fix filtering room types on remote rooms (#17434)

We can only fetch room types for rooms the server is in, so we need to
only filter rooms that we're joined to.

Also includes a perf fix to bulk fetch room types.

1 files changed, 10 insertions, 12 deletions

diff --git a/synapse/handlers/sliding_sync.py b/synapse/handlers/sliding_sync.py
index 818b13621c..8e6c2fb860 100644
--- a/synapse/handlers/sliding_sync.py
+++ b/synapse/handlers/sliding_sync.py
@@ -24,13 +24,7 @@ from typing import TYPE_CHECKING, Any, Dict, Final, List, Optional, Set, Tuple
 import attr
 from immutabledict import immutabledict
 
-from synapse.api.constants import (
-    AccountDataTypes,
-    Direction,
-    EventContentFields,
-    EventTypes,
-    Membership,
-)
+from synapse.api.constants import AccountDataTypes, Direction, EventTypes, Membership
 from synapse.events import EventBase
 from synapse.events.utils import strip_event
 from synapse.handlers.relations import BundledAggregations
@@ -959,11 +953,15 @@ class SlidingSyncHandler:
         # provided in the list. `None` is a valid type for rooms which do not have a
         # room type.
         if filters.room_types is not None or filters.not_room_types is not None:
-            # Make a copy so we don't run into an error: `Set changed size during
-            # iteration`, when we filter out and remove items
-            for room_id in filtered_room_id_set.copy():
-                create_event = await self.store.get_create_event_for_room(room_id)
-                room_type = create_event.content.get(EventContentFields.ROOM_TYPE)
+            room_to_type = await self.store.bulk_get_room_type(
+                {
+                    room_id
+                    for room_id in filtered_room_id_set
+                    # We only know the room types for joined rooms
+                    if sync_room_map[room_id].membership == Membership.JOIN
+                }
+            )
+            for room_id, room_type in room_to_type.items():
                 if (
                     filters.room_types is not None
                     and room_type not in filters.room_types