1 files changed, 106 insertions, 0 deletions
diff --git a/syncapi/storage/postgres/backwards_extremities_table.go b/syncapi/storage/postgres/backwards_extremities_table.go
new file mode 100644
index 00000000..3dd1b234
--- /dev/null
+++ b/syncapi/storage/postgres/backwards_extremities_table.go
@@ -0,0 +1,106 @@
+// Copyright 2018 New Vector Ltd
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package postgres
+
+import (
+	"context"
+	"database/sql"
+
+	"github.com/matrix-org/dendrite/common"
+	"github.com/matrix-org/dendrite/syncapi/storage/tables"
+)
+
+const backwardExtremitiesSchema = `
+-- Stores output room events received from the roomserver.
+CREATE TABLE IF NOT EXISTS syncapi_backward_extremities (
+	-- The 'room_id' key for the event.
+	room_id TEXT NOT NULL,
+	-- The event ID for the last known event. This is the backwards extremity.
+	event_id TEXT NOT NULL,
+	-- The prev_events for the last known event. This is used to update extremities.
+	prev_event_id TEXT NOT NULL,
+	PRIMARY KEY(room_id, event_id, prev_event_id)
+);
+`
+
+const insertBackwardExtremitySQL = "" +
+	"INSERT INTO syncapi_backward_extremities (room_id, event_id, prev_event_id)" +
+	" VALUES ($1, $2, $3)" +
+	" ON CONFLICT DO NOTHING"
+
+const selectBackwardExtremitiesForRoomSQL = "" +
+	"SELECT DISTINCT event_id FROM syncapi_backward_extremities WHERE room_id = $1"
+
+const deleteBackwardExtremitySQL = "" +
+	"DELETE FROM syncapi_backward_extremities WHERE room_id = $1 AND prev_event_id = $2"
+
+type backwardExtremitiesStatements struct {
+	insertBackwardExtremityStmt          *sql.Stmt
+	selectBackwardExtremitiesForRoomStmt *sql.Stmt
+	deleteBackwardExtremityStmt          *sql.Stmt
+}
+
+func NewPostgresBackwardsExtremitiesTable(db *sql.DB) (tables.BackwardsExtremities, error) {
+	s := &backwardExtremitiesStatements{}
+	_, err := db.Exec(backwardExtremitiesSchema)
+	if err != nil {
+		return nil, err
+	}
+	if s.insertBackwardExtremityStmt, err = db.Prepare(insertBackwardExtremitySQL); err != nil {
+		return nil, err
+	}
+	if s.selectBackwardExtremitiesForRoomStmt, err = db.Prepare(selectBackwardExtremitiesForRoomSQL); err != nil {
+		return nil, err
+	}
+	if s.deleteBackwardExtremityStmt, err = db.Prepare(deleteBackwardExtremitySQL); err != nil {
+		return nil, err
+	}
+	return s, nil
+}
+
+func (s *backwardExtremitiesStatements) InsertsBackwardExtremity(
+	ctx context.Context, txn *sql.Tx, roomID, eventID string, prevEventID string,
+) (err error) {
+	_, err = txn.Stmt(s.insertBackwardExtremityStmt).ExecContext(ctx, roomID, eventID, prevEventID)
+	return
+}
+
+func (s *backwardExtremitiesStatements) SelectBackwardExtremitiesForRoom(
+	ctx context.Context, roomID string,
+) (eventIDs []string, err error) {
+	rows, err := s.selectBackwardExtremitiesForRoomStmt.QueryContext(ctx, roomID)
+	if err != nil {
+		return
+	}
+	defer common.CloseAndLogIfError(ctx, rows, "selectBackwardExtremitiesForRoom: rows.close() failed")
+
+	for rows.Next() {
+		var eID string
+		if err = rows.Scan(&eID); err != nil {
+			return
+		}
+
+		eventIDs = append(eventIDs, eID)
+	}
+
+	return eventIDs, rows.Err()
+}
+
+func (s *backwardExtremitiesStatements) DeleteBackwardExtremity(
+	ctx context.Context, txn *sql.Tx, roomID, knownEventID string,
+) (err error) {
+	_, err = txn.Stmt(s.deleteBackwardExtremityStmt).ExecContext(ctx, roomID, knownEventID)
+	return
+}