Return a chunk of events based on the since token

Missing waiting aspect

src/github.com/matrix-org/dendrite/clientapi/storage/output_room_events_table.go

@@ -36,13 +36,17 @@ const insertEventSQL = "" +
 const selectEventsSQL = "" +
 	"SELECT event_json FROM output_room_events WHERE event_id = ANY($1)"
 
+const selectEventsInRangeSQL = "" +
+	"SELECT event_json FROM output_room_events WHERE id >= $1 AND id <= $2"
+
 const selectMaxIDSQL = "" +
 	"SELECT MAX(id) FROM output_room_events"
 
 type outputRoomEventsStatements struct {
-	insertEventStmt  *sql.Stmt
-	selectEventsStmt *sql.Stmt
-	selectMaxIDStmt  *sql.Stmt
+	insertEventStmt         *sql.Stmt
+	selectEventsStmt        *sql.Stmt
+	selectMaxIDStmt         *sql.Stmt
+	selectEventsInRangeStmt *sql.Stmt
 }
 
 func (s *outputRoomEventsStatements) prepare(db *sql.DB) (err error) {
@@ -59,6 +63,9 @@ func (s *outputRoomEventsStatements) prepare(db *sql.DB) (err error) {
 	if s.selectMaxIDStmt, err = db.Prepare(selectMaxIDSQL); err != nil {
 		return
 	}
+	if s.selectEventsInRangeStmt, err = db.Prepare(selectEventsInRangeSQL); err != nil {
+		return
+	}
 	return
 }
 
@@ -69,6 +76,34 @@ func (s *outputRoomEventsStatements) MaxID() (id int64, err error) {
 	return
 }
 
+func (s *outputRoomEventsStatements) InRange(oldPos, newPos int64) ([]gomatrixserverlib.Event, error) {
+	rows, err := s.selectEventsInRangeStmt.Query(oldPos, newPos)
+	if err != nil {
+		return nil, err
+	}
+	defer rows.Close()
+
+	var result []gomatrixserverlib.Event
+	var i int64
+	for ; rows.Next(); i++ {
+		var eventBytes []byte
+		if err := rows.Scan(&eventBytes); err != nil {
+			return nil, err
+		}
+		ev, err := gomatrixserverlib.NewEventFromTrustedJSON(eventBytes, false)
+		if err != nil {
+			return nil, err
+		}
+		result = append(result, ev)
+	}
+	// Expect one event per position, inclusive eg old=3, new=5, expect 3,4,5 so 3 events.
+	wantNum := (1 + newPos - oldPos)
+	if i != wantNum {
+		return nil, fmt.Errorf("failed to map all positions to events: (got %d, wanted, %d)", i, wantNum)
+	}
+	return result, nil
+}
+
 // InsertEvent into the output_room_events table. addState and removeState are an optional list of state event IDs.
 func (s *outputRoomEventsStatements) InsertEvent(txn *sql.Tx, event *gomatrixserverlib.Event, addState, removeState []string) (streamPos int64, err error) {
 	err = txn.Stmt(s.insertEventStmt).QueryRow(

src/github.com/matrix-org/dendrite/clientapi/storage/syncserver.go

@@ -90,6 +90,11 @@ func (d *SyncServerDatabase) SyncStreamPosition() (int64, error) {
 	return d.events.MaxID()
 }
 
+// EventsInRange returns all events in the given range, inclusive.
+func (d *SyncServerDatabase) EventsInRange(oldPos, newPos int64) ([]gomatrixserverlib.Event, error) {
+	return d.events.InRange(oldPos, newPos)
+}
+
 func runTransaction(db *sql.DB, fn func(txn *sql.Tx) error) (err error) {
 	txn, err := db.Begin()
 	if err != nil {

src/github.com/matrix-org/dendrite/clientapi/sync/requestpool.go

@@ -81,12 +81,18 @@ func (rp *RequestPool) OnNewEvent(ev *gomatrixserverlib.Event, pos syncStreamPos
 }
 
 func (rp *RequestPool) currentSyncForUser(req syncRequest) ([]gomatrixserverlib.Event, error) {
+	if req.since == rp.currPos {
+		// wait for new event
+	}
+
+	return rp.db.EventsInRange(int64(req.since), int64(rp.currPos))
+
 	// https://github.com/matrix-org/synapse/blob/v0.19.3/synapse/handlers/sync.py#L179
 	// Check if we are going to return immediately and if so, calculate the current
 	// sync for this user and return.
-	if req.since == 0 || req.timeout == time.Duration(0) || req.wantFullState {
-		return []gomatrixserverlib.Event{}, nil
-	}
+	// if req.since == 0 || req.timeout == time.Duration(0) || req.wantFullState {
+	// 	return []gomatrixserverlib.Event{}, nil
+	// }
 
 	// Steps: (no token)
 	// - get all rooms the user is joined to.