From 90ad4d443a109ad95741b499d914006578acceef Mon Sep 17 00:00:00 2001
From: Jason Robinson <jasonr@matrix.org>
Date: Sat, 9 Jan 2021 21:57:41 +0200
Subject: [PATCH] Implement clearing cache after deleting forward extremities

Also run linter.

Signed-off-by: Jason Robinson <jasonr@matrix.org>
---
 synapse/rest/admin/rooms.py                   | 21 ++++------
 .../main/events_forward_extremities.py        | 41 +++++++++++++++----
 2 files changed, 42 insertions(+), 20 deletions(-)

diff --git a/synapse/rest/admin/rooms.py b/synapse/rest/admin/rooms.py
index 76f860382..6757a8100 100644
--- a/synapse/rest/admin/rooms.py
+++ b/synapse/rest/admin/rooms.py
@@ -524,18 +524,20 @@ class ForwardExtremitiesRestServlet(RestServlet):
     async def resolve_room_id(self, room_identifier: str) -> str:
         """Resolve to a room ID, if necessary."""
         if RoomID.is_valid(room_identifier):
-            room_id = room_identifier
+            resolved_room_id = 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)
-            room_id = room_id.to_string()
+            resolved_room_id = room_id.to_string()
         else:
             raise SynapseError(
                 400, "%s was not legal room ID or room alias" % (room_identifier,)
             )
-        if not room_id:
-            raise SynapseError(400, "Unknown room ID or room alias %s" % room_identifier)
-        return room_id
+        if not resolved_room_id:
+            raise SynapseError(
+                400, "Unknown room ID or room alias %s" % room_identifier
+            )
+        return resolved_room_id
 
     async def on_DELETE(self, request, room_identifier):
         requester = await self.auth.get_user_by_req(request)
@@ -544,9 +546,7 @@ class ForwardExtremitiesRestServlet(RestServlet):
         room_id = await self.resolve_room_id(room_identifier)
 
         deleted_count = await self.store.delete_forward_extremities_for_room(room_id)
-        return 200, {
-            "deleted": deleted_count,
-        }
+        return 200, {"deleted": deleted_count}
 
     async def on_GET(self, request, room_identifier):
         requester = await self.auth.get_user_by_req(request)
@@ -555,7 +555,4 @@ class ForwardExtremitiesRestServlet(RestServlet):
         room_id = await self.resolve_room_id(room_identifier)
 
         extremities = await self.store.get_forward_extremities_for_room(room_id)
-        return 200, {
-            "count": len(extremities),
-            "results": extremities,
-        }
+        return 200, {"count": len(extremities), "results": extremities}
diff --git a/synapse/storage/databases/main/events_forward_extremities.py b/synapse/storage/databases/main/events_forward_extremities.py
index cc684a94f..6b8da52fe 100644
--- a/synapse/storage/databases/main/events_forward_extremities.py
+++ b/synapse/storage/databases/main/events_forward_extremities.py
@@ -1,15 +1,22 @@
-from typing import List, Dict
+import logging
+from typing import Dict, List
 
+from synapse.api.errors import SynapseError
 from synapse.storage._base import SQLBaseStore
 
+logger = logging.getLogger(__name__)
+
 
 class EventForwardExtremitiesStore(SQLBaseStore):
-
     async def delete_forward_extremities_for_room(self, room_id: str) -> int:
         """Delete any extra forward extremities for a room.
 
+        Invalidates the "get_latest_event_ids_in_room" cache if any forward
+        extremities were deleted.
+
         Returns count deleted.
         """
+
         def delete_forward_extremities_for_room_txn(txn):
             # First we need to get the event_id to not delete
             sql = (
@@ -27,9 +34,17 @@ class EventForwardExtremitiesStore(SQLBaseStore):
             )
             txn.execute(sql, (room_id,))
             rows = txn.fetchall()
-
-            # TODO: should this raise a SynapseError instead of better to blow?
-            event_id = rows[0][0]
+            try:
+                event_id = rows[0][0]
+                logger.debug(
+                    "Found event_id %s as the forward extremity to keep for room %s",
+                    event_id,
+                    room_id,
+                )
+            except KeyError:
+                msg = f"No forward extremity event found for room {room_id}"
+                logger.warning(msg)
+                raise SynapseError(400, msg)
 
             # Now delete the extra forward extremities
             sql = (
@@ -39,19 +54,29 @@ class EventForwardExtremitiesStore(SQLBaseStore):
                 "   AND room_id = ?"
             )
 
-            # TODO we should not commit yet
             txn.execute(sql, (event_id, room_id))
+            logger.info(
+                "Deleted %s extra forward extremities for room %s",
+                txn.rowcount,
+                room_id,
+            )
 
-            # TODO flush the cache then commit
+            if txn.rowcount > 0:
+                # Invalidate the cache
+                self._invalidate_cache_and_stream(
+                    txn, self.get_latest_event_ids_in_room, (room_id,),
+                )
 
             return txn.rowcount
 
         return await self.db_pool.runInteraction(
-            "delete_forward_extremities_for_room", delete_forward_extremities_for_room_txn,
+            "delete_forward_extremities_for_room",
+            delete_forward_extremities_for_room_txn,
         )
 
     async def get_forward_extremities_for_room(self, room_id: str) -> List[Dict]:
         """Get list of forward extremities for a room."""
+
         def get_forward_extremities_for_room_txn(txn):
             sql = (
                 "SELECT event_id, state_group FROM event_forward_extremities NATURAL JOIN event_to_state_groups "