Add a new component: currentstateserver (#1171)

* Add a new component: currentstateserver

- Add a skeleton for it, with databases and a single query method.
- Add integration tests for it.
- Add listen/address fields in the config (breaking as this will force people to specify this to validate)

Not currently hooked up to anything yet.

* Unbreak config tests

* Add current_state to sample config

* comments

currentstateserver/storage/storage_wasm.go

@@ -0,0 +1,42 @@
+// Copyright 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 storage
+
+import (
+	"fmt"
+	"net/url"
+
+	"github.com/matrix-org/dendrite/currentstateserver/storage/sqlite3"
+	"github.com/matrix-org/dendrite/internal/sqlutil"
+)
+
+// NewDatabase opens a database connection.
+func NewDatabase(
+	dataSourceName string,
+	dbProperties sqlutil.DbProperties, // nolint:unparam
+) (Database, error) {
+	uri, err := url.Parse(dataSourceName)
+	if err != nil {
+		return nil, fmt.Errorf("Cannot use postgres implementation")
+	}
+	switch uri.Scheme {
+	case "postgres":
+		return nil, fmt.Errorf("Cannot use postgres implementation")
+	case "file":
+		return sqlite3.NewDatabase(dataSourceName)
+	default:
+		return nil, fmt.Errorf("Cannot use postgres implementation")
+	}
+}