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/rest/admin/__init__.py

@@ -36,6 +36,7 @@ from synapse.rest.admin.media import ListMediaInRoom, register_servlets_for_medi
 from synapse.rest.admin.purge_room_servlet import PurgeRoomServlet
 from synapse.rest.admin.rooms import (
     DeleteRoomRestServlet,
+    ForwardExtremitiesRestServlet,
     JoinRoomAliasServlet,
     ListRoomRestServlet,
     MakeRoomAdminRestServlet,
@@ -230,6 +231,7 @@ def register_servlets(hs, http_server):
     EventReportsRestServlet(hs).register(http_server)
     PushersRestServlet(hs).register(http_server)
     MakeRoomAdminRestServlet(hs).register(http_server)
+    ForwardExtremitiesRestServlet(hs).register(http_server)
 
 
 def register_servlets_for_client_rest_resource(hs, http_server):

synapse/rest/admin/rooms.py

@@ -499,3 +499,56 @@ class MakeRoomAdminRestServlet(RestServlet):
         )
 
         return 200, {}
+
+
+class ForwardExtremitiesRestServlet(RestServlet):
+    """Allows a server admin to get or clear forward extremities.
+
+    Clearing does not require restarting the server.
+
+        Clear forward extremities:
+        DELETE /_synapse/admin/v1/rooms/<room_id_or_alias>/forward_extremities
+
+        Get forward_extremities:
+        GET /_synapse/admin/v1/rooms/<room_id_or_alias>/forward_extremities
+    """
+
+    PATTERNS = admin_patterns("/rooms/(?P<room_identifier>[^/]*)/forward_extremities")
+
+    def __init__(self, hs: "HomeServer"):
+        self.hs = hs
+        self.auth = hs.get_auth()
+        self.room_member_handler = hs.get_room_member_handler()
+        self.store = hs.get_datastore()
+
+    async def resolve_room_id(self, room_identifier: str) -> str:
+        """Resolve to a room ID, if necessary."""
+        if RoomID.is_valid(room_identifier):
+            return room_identifier
+        elif RoomAlias.is_valid(room_identifier):
+            room_alias = RoomAlias.from_string(room_identifier)
+            room_id, _ = await self.room_member_handler.lookup_room_alias(room_alias)
+            return room_id.to_string()
+        raise SynapseError(
+            400, "%s was not legal room ID or room alias" % (room_identifier,)
+        )
+
+    async def on_DELETE(self, request, room_identifier):
+        requester = await self.auth.get_user_by_req(request)
+        await assert_user_is_admin(self.auth, requester.user)
+
+        room_id = await self.resolve_room_id(room_identifier)
+
+    async def on_GET(self, request, room_identifier):
+        requester = await self.auth.get_user_by_req(request)
+        await assert_user_is_admin(self.auth, requester.user)
+
+        room_id = await self.resolve_room_id(room_identifier)
+        if not room_id:
+            raise SynapseError(400, "Unknown room ID or room alias %s" % room_identifier)
+
+        extremities = await self.store.get_forward_extremities_for_room(room_id)
+        return 200, {
+            "count": len(extremities),
+            "results": extremities,
+        }

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
+        )