Add forward extremities endpoint to rooms admin API

GET /_synapse/admin/v1/rooms/<identifier>/forward_extremities now gets forward extremities for a room, returning count and the list of extremities.

Signed-off-by: Jason Robinson <jasonr@matrix.org>

synapse/storage/databases/main/__init__.py

@@ -43,6 +43,7 @@ from .end_to_end_keys import EndToEndKeyStore
 from .event_federation import EventFederationStore
 from .event_push_actions import EventPushActionsStore
 from .events_bg_updates import EventsBackgroundUpdatesStore
+from .events_forward_extremities import EventForwardExtremitiesStore
 from .filtering import FilteringStore
 from .group_server import GroupServerStore
 from .keys import KeyStore
@@ -118,6 +119,7 @@ class DataStore(
     UIAuthStore,
     CacheInvalidationWorkerStore,
     ServerMetricsStore,
+    EventForwardExtremitiesStore,
 ):
     def __init__(self, database: DatabasePool, db_conn, hs):
         self.hs = hs

synapse/storage/databases/main/events_forward_extremities.py

@@ -0,0 +1,20 @@
+from typing import List, Dict
+
+from synapse.storage._base import SQLBaseStore
+
+
+class EventForwardExtremitiesStore(SQLBaseStore):
+    async def get_forward_extremities_for_room(self, room_id: str) -> List[Dict]:
+        def get_forward_extremities_for_room_txn(txn):
+            sql = (
+                "SELECT event_id, state_group FROM event_forward_extremities NATURAL JOIN event_to_state_groups "
+                "WHERE room_id = ?"
+            )
+
+            txn.execute(sql, (room_id,))
+            rows = txn.fetchall()
+            return [{"event_id": row[0], "state_group": row[1]} for row in rows]
+
+        return await self.db_pool.runInteraction(
+            "get_forward_extremities_for_room", get_forward_extremities_for_room_txn
+        )