From 077a23fea03571bc8e25db8ce26bc5fc4c3bd892 Mon Sep 17 00:00:00 2001
From: Neil Alexander <neilalexander@users.noreply.github.com>
Date: Wed, 14 Oct 2020 11:52:32 +0100
Subject: [PATCH] Resolve state

---
 roomserver/internal/query/query.go | 20 +++++++++++++++++++-
 1 file changed, 19 insertions(+), 1 deletion(-)

diff --git a/roomserver/internal/query/query.go b/roomserver/internal/query/query.go
index 65fc66ca0..ecfb580f2 100644
--- a/roomserver/internal/query/query.go
+++ b/roomserver/internal/query/query.go
@@ -49,6 +49,7 @@ func (r *Queryer) QueryLatestEventsAndState(
 }
 
 // QueryStateAfterEvents implements api.RoomserverInternalAPI
+// nolint:gocyclo
 func (r *Queryer) QueryStateAfterEvents(
 	ctx context.Context,
 	request *api.QueryStateAfterEventsRequest,
@@ -81,7 +82,6 @@ func (r *Queryer) QueryStateAfterEvents(
 	var stateEntries []types.StateEntry
 	if len(request.StateToFetch) == 0 {
 		// Look up all of the current room state.
-		// TODO: This can return duplicate state-key tuples, is this a problem?
 		stateEntries, err = roomState.LoadCombinedStateAfterEvents(
 			ctx, prevStates,
 		)
@@ -100,6 +100,24 @@ func (r *Queryer) QueryStateAfterEvents(
 		return err
 	}
 
+	if len(request.PrevEventIDs) > 1 && len(request.StateToFetch) == 0 {
+		var authEventIDs []string
+		for _, e := range stateEvents {
+			authEventIDs = append(authEventIDs, e.AuthEventIDs()...)
+		}
+		authEventIDs = util.UniqueStrings(authEventIDs)
+
+		authEvents, err := getAuthChain(ctx, r.DB.EventsFromIDs, authEventIDs)
+		if err != nil {
+			return fmt.Errorf("getAuthChain: %w", err)
+		}
+
+		stateEvents, err = state.ResolveConflictsAdhoc(info.RoomVersion, stateEvents, authEvents)
+		if err != nil {
+			return fmt.Errorf("state.ResolveConflictsAdhoc: %w", err)
+		}
+	}
+
 	for _, event := range stateEvents {
 		response.StateEvents = append(response.StateEvents, event.Headered(info.RoomVersion))
 	}