More SQLite (#871)

* SQLite support for appservice

* SQLite support for mediaapi

* Copyright notices

* SQLite for public rooms API (although with some slight differences in behaviour)

* Lazy match aliases, add TODOs

appservice/storage/sqlite3/txn_id_counter_table.go

@@ -0,0 +1,60 @@
+// Copyright 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 sqlite3
+
+import (
+	"context"
+	"database/sql"
+)
+
+const txnIDSchema = `
+-- Keeps a count of the current transaction ID
+CREATE TABLE IF NOT EXISTS appservice_counters (
+  name TEXT PRIMARY KEY NOT NULL,
+  last_id INTEGER DEFAULT 1
+);
+INSERT OR IGNORE INTO appservice_counters (name, last_id) VALUES('txn_id', 1);
+`
+
+const selectTxnIDSQL = `
+  SELECT last_id FROM appservice_counters WHERE name='txn_id';
+  UPDATE appservice_counters SET last_id=last_id+1 WHERE name='txn_id';
+`
+
+type txnStatements struct {
+	selectTxnIDStmt *sql.Stmt
+}
+
+func (s *txnStatements) prepare(db *sql.DB) (err error) {
+	_, err = db.Exec(txnIDSchema)
+	if err != nil {
+		return
+	}
+
+	if s.selectTxnIDStmt, err = db.Prepare(selectTxnIDSQL); err != nil {
+		return
+	}
+
+	return
+}
+
+// selectTxnID selects the latest ascending transaction ID
+func (s *txnStatements) selectTxnID(
+	ctx context.Context,
+) (txnID int, err error) {
+	err = s.selectTxnIDStmt.QueryRowContext(ctx).Scan(&txnID)
+	return
+}