Correctly generate backpagination tokens for events which have the same depth (#996)

* Correctly generate backpagination tokens for events which have the same depth

With tests. Unfortunately the code around here is hard to understand.
There will be a subsequent PR which fixes this up now that we have a test
harness in place.

* Add postgres impl

* More linting

* Fix psql statement so it actually works

1 files changed, 12 insertions, 6 deletions

diff --git a/syncapi/storage/postgres/syncserver.go b/syncapi/storage/postgres/syncserver.go
index ef970739..744ae7b8 100644
--- a/syncapi/storage/postgres/syncserver.go
+++ b/syncapi/storage/postgres/syncserver.go
@@ -159,7 +159,7 @@ func (d *SyncServerDatasource) WriteEvent(
 		}
 		pduPosition = pos
 
-		if err = d.topology.insertEventInTopology(ctx, ev); err != nil {
+		if err = d.topology.insertEventInTopology(ctx, ev, pos); err != nil {
 			return err
 		}
 
@@ -240,12 +240,13 @@ func (d *SyncServerDatasource) GetEventsInRange(
 	if from.Type == types.PaginationTokenTypeTopology {
 		// Determine the backward and forward limit, i.e. the upper and lower
 		// limits to the selection in the room's topology, from the direction.
-		var backwardLimit, forwardLimit types.StreamPosition
+		var backwardLimit, forwardLimit, forwardMicroLimit types.StreamPosition
 		if backwardOrdering {
 			// Backward ordering is antichronological (latest event to oldest
 			// one).
 			backwardLimit = to.PDUPosition
 			forwardLimit = from.PDUPosition
+			forwardMicroLimit = from.EDUTypingPosition
 		} else {
 			// Forward ordering is chronological (oldest event to latest one).
 			backwardLimit = from.PDUPosition
@@ -255,7 +256,7 @@ func (d *SyncServerDatasource) GetEventsInRange(
 		// Select the event IDs from the defined range.
 		var eIDs []string
 		eIDs, err = d.topology.selectEventIDsInRange(
-			ctx, roomID, backwardLimit, forwardLimit, limit, !backwardOrdering,
+			ctx, roomID, backwardLimit, forwardLimit, forwardMicroLimit, limit, !backwardOrdering,
 		)
 		if err != nil {
 			return
@@ -301,7 +302,7 @@ func (d *SyncServerDatasource) BackwardExtremitiesForRoom(
 
 func (d *SyncServerDatasource) MaxTopologicalPosition(
 	ctx context.Context, roomID string,
-) (types.StreamPosition, error) {
+) (depth types.StreamPosition, stream types.StreamPosition, err error) {
 	return d.topology.selectMaxPositionInTopology(ctx, roomID)
 }
 
@@ -318,8 +319,13 @@ func (d *SyncServerDatasource) EventsAtTopologicalPosition(
 
 func (d *SyncServerDatasource) EventPositionInTopology(
 	ctx context.Context, eventID string,
-) (types.StreamPosition, error) {
-	return d.topology.selectPositionInTopology(ctx, eventID)
+) (depth types.StreamPosition, stream types.StreamPosition, err error) {
+	depth, err = d.topology.selectPositionInTopology(ctx, eventID)
+	if err != nil {
+		return
+	}
+	stream, err = d.events.selectStreamPositionForEventID(ctx, eventID)
+	return
 }
 
 func (d *SyncServerDatasource) SyncStreamPosition(ctx context.Context) (types.StreamPosition, error) {