Cross-signing fixes, notifications via sync, federation (#1974)

* Initial work on signing key update EDUs

* Fix build

* Produce/consume EDUs

* Producer logging

* Only produce key change notifications for local users

* Better naming

* Try to notify sync

* Enable feature

* Use key change topic

* Don't bother verifying signatures, validate key lengths if we can, notifier fixes

* Copyright notices

* Remove tests from whitelist until matrix-org/sytest#1117

* Some review comment fixes

* Update to matrix-org/gomatrixserverlib@f9416ac

* Remove unneeded parameter

federationsender/consumers/keychange.go

@@ -20,6 +20,7 @@ import (
 	"fmt"
 
 	"github.com/Shopify/sarama"
+	eduserverAPI "github.com/matrix-org/dendrite/eduserver/api"
 	"github.com/matrix-org/dendrite/federationsender/queue"
 	"github.com/matrix-org/dendrite/federationsender/storage"
 	"github.com/matrix-org/dendrite/internal"
@@ -28,6 +29,7 @@ import (
 	"github.com/matrix-org/dendrite/setup/config"
 	"github.com/matrix-org/dendrite/setup/process"
 	"github.com/matrix-org/gomatrixserverlib"
+	"github.com/sirupsen/logrus"
 	log "github.com/sirupsen/logrus"
 )
 
@@ -83,6 +85,17 @@ func (t *KeyChangeConsumer) onMessage(msg *sarama.ConsumerMessage) error {
 		log.WithError(err).Errorf("failed to read device message from key change topic")
 		return nil
 	}
+	switch m.Type {
+	case api.TypeCrossSigningUpdate:
+		return t.onCrossSigningMessage(m)
+	case api.TypeDeviceKeyUpdate:
+		fallthrough
+	default:
+		return t.onDeviceKeyMessage(m)
+	}
+}
+
+func (t *KeyChangeConsumer) onDeviceKeyMessage(m api.DeviceMessage) error {
 	logger := log.WithField("user_id", m.UserID)
 
 	// only send key change events which originated from us
@@ -133,6 +146,50 @@ func (t *KeyChangeConsumer) onMessage(msg *sarama.ConsumerMessage) error {
 	return t.queues.SendEDU(edu, t.serverName, destinations)
 }
 
+func (t *KeyChangeConsumer) onCrossSigningMessage(m api.DeviceMessage) error {
+	output := m.CrossSigningKeyUpdate
+	_, host, err := gomatrixserverlib.SplitID('@', output.UserID)
+	if err != nil {
+		logrus.WithError(err).Errorf("fedsender key change consumer: user ID parse failure")
+		return nil
+	}
+	if host != gomatrixserverlib.ServerName(t.serverName) {
+		// Ignore any messages that didn't originate locally, otherwise we'll
+		// end up parroting information we received from other servers.
+		return nil
+	}
+	logger := log.WithField("user_id", output.UserID)
+
+	var queryRes roomserverAPI.QueryRoomsForUserResponse
+	err = t.rsAPI.QueryRoomsForUser(context.Background(), &roomserverAPI.QueryRoomsForUserRequest{
+		UserID:         output.UserID,
+		WantMembership: "join",
+	}, &queryRes)
+	if err != nil {
+		logger.WithError(err).Error("fedsender key change consumer: failed to calculate joined rooms for user")
+		return nil
+	}
+	// send this key change to all servers who share rooms with this user.
+	destinations, err := t.db.GetJoinedHostsForRooms(context.Background(), queryRes.RoomIDs)
+	if err != nil {
+		logger.WithError(err).Error("fedsender key change consumer: failed to calculate joined hosts for rooms user is in")
+		return nil
+	}
+
+	// Pack the EDU and marshal it
+	edu := &gomatrixserverlib.EDU{
+		Type:   eduserverAPI.MSigningKeyUpdate,
+		Origin: string(t.serverName),
+	}
+	if edu.Content, err = json.Marshal(output); err != nil {
+		logger.WithError(err).Error("fedsender key change consumer: failed to marshal output, dropping")
+		return nil
+	}
+
+	logger.Infof("Sending cross-signing update message to %q", destinations)
+	return t.queues.SendEDU(edu, t.serverName, destinations)
+}
+
 func prevID(streamID int) []int {
 	if streamID <= 1 {
 		return nil