Fix missing sync events during historical batch imports (#12319)

Discovered after much in-depth investigation in #12281.

Closes: #12281
Closes: #3305

Signed off by: Nick Mills-Barrett nick@beeper.com

1 files changed, 5 insertions, 9 deletions

diff --git a/synapse/handlers/message.py b/synapse/handlers/message.py
index 47a63005a9..1b092e900e 100644
--- a/synapse/handlers/message.py
+++ b/synapse/handlers/message.py
@@ -175,17 +175,13 @@ class MessageHandler:
         state_filter = state_filter or StateFilter.all()
 
         if at_token:
-            # FIXME this claims to get the state at a stream position, but
-            # get_recent_events_for_room operates by topo ordering. This therefore
-            # does not reliably give you the state at the given stream position.
-            # (https://github.com/matrix-org/synapse/issues/3305)
-            last_events, _ = await self.store.get_recent_events_for_room(
-                room_id, end_token=at_token.room_key, limit=1
+            last_event = await self.store.get_last_event_in_room_before_stream_ordering(
+                room_id,
+                end_token=at_token.room_key,
             )
 
-            if not last_events:
+            if not last_event:
                 raise NotFoundError("Can't find event for token %s" % (at_token,))
-            last_event = last_events[0]
 
             # check whether the user is in the room at that time to determine
             # whether they should be treated as peeking.
@@ -204,7 +200,7 @@ class MessageHandler:
             visible_events = await filter_events_for_client(
                 self.storage,
                 user_id,
-                last_events,
+                [last_event],
                 filter_send_to_client=False,
                 is_peeking=is_peeking,
             )