Implement storage interfaces (#841)

* Implement interfaces for federationsender storage

* Implement interfaces for mediaapi storage

* Implement interfaces for publicroomsapi storage

* Implement interfaces for roomserver storage

* Implement interfaces for syncapi storage

* Implement interfaces for keydb storage

* common.PartitionStorer in publicroomsapi interface

* Update copyright notices

federationsender/storage/postgres/room_table.go

@@ -0,0 +1,101 @@
+// Copyright 2017-2018 New Vector Ltd
+// Copyright 2019-2020 The Matrix.org Foundation C.I.C.
+//
+// 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"
+)
+
+const roomSchema = `
+CREATE TABLE IF NOT EXISTS federationsender_rooms (
+    -- The string ID of the room
+    room_id TEXT PRIMARY KEY,
+    -- The most recent event state by the room server.
+    -- We can use this to tell if our view of the room state has become
+    -- desynchronised.
+    last_event_id TEXT NOT NULL
+);`
+
+const insertRoomSQL = "" +
+	"INSERT INTO federationsender_rooms (room_id, last_event_id) VALUES ($1, '')" +
+	" ON CONFLICT DO NOTHING"
+
+const selectRoomForUpdateSQL = "" +
+	"SELECT last_event_id FROM federationsender_rooms WHERE room_id = $1 FOR UPDATE"
+
+const updateRoomSQL = "" +
+	"UPDATE federationsender_rooms SET last_event_id = $2 WHERE room_id = $1"
+
+type roomStatements struct {
+	insertRoomStmt          *sql.Stmt
+	selectRoomForUpdateStmt *sql.Stmt
+	updateRoomStmt          *sql.Stmt
+}
+
+func (s *roomStatements) prepare(db *sql.DB) (err error) {
+	_, err = db.Exec(roomSchema)
+	if err != nil {
+		return
+	}
+
+	if s.insertRoomStmt, err = db.Prepare(insertRoomSQL); err != nil {
+		return
+	}
+	if s.selectRoomForUpdateStmt, err = db.Prepare(selectRoomForUpdateSQL); err != nil {
+		return
+	}
+	if s.updateRoomStmt, err = db.Prepare(updateRoomSQL); err != nil {
+		return
+	}
+	return
+}
+
+// insertRoom inserts the room if it didn't already exist.
+// If the room didn't exist then last_event_id is set to the empty string.
+func (s *roomStatements) insertRoom(
+	ctx context.Context, txn *sql.Tx, roomID string,
+) error {
+	_, err := common.TxStmt(txn, s.insertRoomStmt).ExecContext(ctx, roomID)
+	return err
+}
+
+// selectRoomForUpdate locks the row for the room and returns the last_event_id.
+// The row must already exist in the table. Callers can ensure that the row
+// exists by calling insertRoom first.
+func (s *roomStatements) selectRoomForUpdate(
+	ctx context.Context, txn *sql.Tx, roomID string,
+) (string, error) {
+	var lastEventID string
+	stmt := common.TxStmt(txn, s.selectRoomForUpdateStmt)
+	err := stmt.QueryRowContext(ctx, roomID).Scan(&lastEventID)
+	if err != nil {
+		return "", err
+	}
+	return lastEventID, nil
+}
+
+// updateRoom updates the last_event_id for the room. selectRoomForUpdate should
+// have already been called earlier within the transaction.
+func (s *roomStatements) updateRoom(
+	ctx context.Context, txn *sql.Tx, roomID, lastEventID string,
+) error {
+	stmt := common.TxStmt(txn, s.updateRoomStmt)
+	_, err := stmt.ExecContext(ctx, roomID, lastEventID)
+	return err
+}