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/tables/interface.go

@@ -0,0 +1,31 @@
+// 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 tables
+
+import (
+	"context"
+	"database/sql"
+
+	"github.com/matrix-org/gomatrixserverlib"
+)
+
+type CurrentRoomState interface {
+	SelectStateEvent(ctx context.Context, roomID, evType, stateKey string) (*gomatrixserverlib.HeaderedEvent, error)
+	SelectEventsWithEventIDs(ctx context.Context, txn *sql.Tx, eventIDs []string) ([]gomatrixserverlib.HeaderedEvent, error)
+	UpsertRoomState(ctx context.Context, txn *sql.Tx, event gomatrixserverlib.HeaderedEvent, membership *string) error
+	DeleteRoomStateByEventID(ctx context.Context, txn *sql.Tx, eventID string) error
+	// SelectRoomIDsWithMembership returns the list of room IDs which have the given user in the given membership state.
+	SelectRoomIDsWithMembership(ctx context.Context, txn *sql.Tx, userID string, membership string) ([]string, error)
+}