make the hack accumulate state properly

sync2/poller.go

@@ -891,22 +891,37 @@ func (p *poller) parseRoomsResponse(ctx context.Context, res *SyncResponse) erro
 }
 
 func tempHackMakeTimelineLimited(s *SyncV2JoinResponse) {
-	var timelineState []json.RawMessage
-	var timelineMsgs []json.RawMessage
+	// Build a state map using the state block.
+	state := make(map[[2]string]json.RawMessage)
+	for _, event := range s.State.Events {
+		parsed := gjson.ParseBytes(event)
+		key := [2]string{parsed.Get("type").Str, parsed.Get("state_key").Str}
+		state[key] = event
+	}
 
+	// Scan the timeline. Add state events to the state block, dumping the rest of the
+	// timeline messages into an array.
+	var timelineMsgs []json.RawMessage
 	for _, event := range s.Timeline.Events {
-		if gjson.GetBytes(event, "state_key").Exists() {
-			timelineState = append(timelineState, event)
+		parsed := gjson.ParseBytes(event)
+		if parsed.Get("state_key").Exists() {
+			key := [2]string{parsed.Get("type").Str, parsed.Get("state_key").Str}
+			state[key] = event
 		} else {
 			timelineMsgs = append(timelineMsgs, event)
 		}
 	}
 
-	if len(timelineState) > 0 {
+	// If we found at least one state event in the timeline, edit the response in-place
+	// to make it look like a limited sync.
+	if len(state) > len(s.State.Events) {
+		logger.Debug().Msgf("HACK: move %d state events to state block and mark as limited", len(state)-len(s.State.Events))
 		s.Timeline.Limited = true
 		s.Timeline.Events = timelineMsgs
-		s.State.Events = append(s.State.Events, timelineState...)
-		logger.Debug().Msgf("HACK: move %d state events to state block and mark as limited", len(timelineState))
+		s.State.Events = make([]json.RawMessage, 0, len(state))
+		for _, event := range state {
+			s.State.Events = append(s.State.Events, event)
+		}
 	}
 }