Loopback event from invite response (#982)

* Working invite v2 support

* Fix copyright notice

* Update gomatrixserverlib

* Add fallthrough

* Add missing continue

* Update sytest-whitelist, gomatrixserverlib

* Update gomatrixserverlib to test matrix-org/gomatrixserverlib#181

* Update gomatrixserverlib

federationsender/producers/roomserver.go

@@ -0,0 +1,66 @@
+// 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 producers
+
+import (
+	"context"
+
+	"github.com/matrix-org/dendrite/roomserver/api"
+	"github.com/matrix-org/gomatrixserverlib"
+)
+
+// RoomserverProducer produces events for the roomserver to consume.
+type RoomserverProducer struct {
+	InputAPI   api.RoomserverInputAPI
+	serverName gomatrixserverlib.ServerName
+}
+
+// NewRoomserverProducer creates a new RoomserverProducer
+func NewRoomserverProducer(
+	inputAPI api.RoomserverInputAPI, serverName gomatrixserverlib.ServerName,
+) *RoomserverProducer {
+	return &RoomserverProducer{
+		InputAPI:   inputAPI,
+		serverName: serverName,
+	}
+}
+
+// SendInviteResponse drops an invite response back into the roomserver so that users
+// already in the room will be notified of the new invite. The invite response is signed
+// by the remote side.
+func (c *RoomserverProducer) SendInviteResponse(
+	ctx context.Context, res gomatrixserverlib.RespInviteV2, roomVersion gomatrixserverlib.RoomVersion,
+) (string, error) {
+	ev := res.Event.Headered(roomVersion)
+	ire := api.InputRoomEvent{
+		Kind:          api.KindNew,
+		Event:         ev,
+		AuthEventIDs:  ev.AuthEventIDs(),
+		SendAsServer:  string(c.serverName),
+		TransactionID: nil,
+	}
+	return c.SendInputRoomEvents(ctx, []api.InputRoomEvent{ire})
+}
+
+// SendInputRoomEvents writes the given input room events to the roomserver input API.
+func (c *RoomserverProducer) SendInputRoomEvents(
+	ctx context.Context, ires []api.InputRoomEvent,
+) (eventID string, err error) {
+	request := api.InputRoomEventsRequest{InputRoomEvents: ires}
+	var response api.InputRoomEventsResponse
+	err = c.InputAPI.InputRoomEvents(ctx, &request, &response)
+	eventID = response.EventID
+	return
+}