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.

2 files changed, 61 insertions, 13 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
diff --git a/synapse/storage/databases/main/state.py b/synapse/storage/databases/main/state.py
index b2a67aff89..5188b2f7a4 100644
--- a/synapse/storage/databases/main/state.py
+++ b/synapse/storage/databases/main/state.py
@@ -41,7 +41,7 @@ from typing import (
 
 import attr
 
-from synapse.api.constants import EventTypes, Membership
+from synapse.api.constants import EventContentFields, EventTypes, Membership
 from synapse.api.errors import NotFoundError, UnsupportedRoomVersionError
 from synapse.api.room_versions import KNOWN_ROOM_VERSIONS, RoomVersion
 from synapse.events import EventBase
@@ -298,6 +298,56 @@ class StateGroupWorkerStore(EventsWorkerStore, SQLBaseStore):
         create_event = await self.get_event(create_id)
         return create_event
 
+    @cached(max_entries=10000)
+    async def get_room_type(self, room_id: str) -> Optional[str]:
+        """Get the room type for a given room. The server must be joined to the
+        given room.
+        """
+
+        row = await self.db_pool.simple_select_one(
+            table="room_stats_state",
+            keyvalues={"room_id": room_id},
+            retcols=("room_type",),
+            allow_none=True,
+            desc="get_room_type",
+        )
+
+        if row is not None:
+            return row[0]
+
+        # If we haven't updated `room_stats_state` with the room yet, query the
+        # create event directly.
+        create_event = await self.get_create_event_for_room(room_id)
+        room_type = create_event.content.get(EventContentFields.ROOM_TYPE)
+        return room_type
+
+    @cachedList(cached_method_name="get_room_type", list_name="room_ids")
+    async def bulk_get_room_type(
+        self, room_ids: Set[str]
+    ) -> Mapping[str, Optional[str]]:
+        """Bulk fetch room types for the given rooms, the server must be in all
+        the rooms given.
+        """
+
+        rows = await self.db_pool.simple_select_many_batch(
+            table="room_stats_state",
+            column="room_id",
+            iterable=room_ids,
+            retcols=("room_id", "room_type"),
+            desc="bulk_get_room_type",
+        )
+
+        # If we haven't updated `room_stats_state` with the room yet, query the
+        # create events directly. This should happen only rarely so we don't
+        # mind if we do this in a loop.
+        results = dict(rows)
+        for room_id in room_ids - results.keys():
+            create_event = await self.get_create_event_for_room(room_id)
+            room_type = create_event.content.get(EventContentFields.ROOM_TYPE)
+            results[room_id] = room_type
+
+        return results
+
     @cached(max_entries=100000, iterable=True)
     async def get_partial_current_state_ids(self, room_id: str) -> StateMap[str]:
         """Get the current state event ids for a room based on the