Fix bug where state events could be requested twice in appservices (#2328)

* Fix bug where state events could be requested twice (should fix #2305)

* Avoid a pointless HTTP request if possible

1 files changed, 15 insertions, 6 deletions

diff --git a/appservice/consumers/roomserver.go b/appservice/consumers/roomserver.go
index 01790722..31e05caa 100644
--- a/appservice/consumers/roomserver.go
+++ b/appservice/consumers/roomserver.go
@@ -83,20 +83,29 @@ func (s *OutputRoomEventConsumer) onMessage(ctx context.Context, msg *nats.Msg)
 		return true
 	}
 
-	if output.Type != api.OutputTypeNewRoomEvent {
+	if output.Type != api.OutputTypeNewRoomEvent || output.NewRoomEvent == nil {
 		return true
 	}
 
-	events := []*gomatrixserverlib.HeaderedEvent{output.NewRoomEvent.Event}
+	newEventID := output.NewRoomEvent.Event.EventID()
+	events := make([]*gomatrixserverlib.HeaderedEvent, 0, len(output.NewRoomEvent.AddsStateEventIDs))
+	events = append(events, output.NewRoomEvent.Event)
 	if len(output.NewRoomEvent.AddsStateEventIDs) > 0 {
 		eventsReq := &api.QueryEventsByIDRequest{
-			EventIDs: output.NewRoomEvent.AddsStateEventIDs,
+			EventIDs: make([]string, 0, len(output.NewRoomEvent.AddsStateEventIDs)),
 		}
 		eventsRes := &api.QueryEventsByIDResponse{}
-		if err := s.rsAPI.QueryEventsByID(s.ctx, eventsReq, eventsRes); err != nil {
-			return false
+		for _, eventID := range output.NewRoomEvent.AddsStateEventIDs {
+			if eventID != newEventID {
+				eventsReq.EventIDs = append(eventsReq.EventIDs, eventID)
+			}
+		}
+		if len(eventsReq.EventIDs) > 0 {
+			if err := s.rsAPI.QueryEventsByID(s.ctx, eventsReq, eventsRes); err != nil {
+				return false
+			}
+			events = append(events, eventsRes.Events...)
 		}
-		events = append(events, eventsRes.Events...)
 	}
 
 	// Send event to any relevant application services