bugfix: when a user's key changes, don't notify everyone on the server (#1253)

* bugfix: when a user's key changes, don't notify everyone on the server

Instead just notify the users you share a room with.

* Update whitelist

syncapi/internal/keychange.go

@@ -95,6 +95,8 @@ func DeviceListCatchup(
 		util.GetLogger(ctx).WithError(queryRes.Error).Error("QueryKeyChanges failed")
 		return hasNew, nil
 	}
+	// QueryKeyChanges gets ALL users who have changed keys, we want the ones who share rooms with the user.
+	queryRes.UserIDs = filterSharedUsers(ctx, stateAPI, userID, queryRes.UserIDs)
 	util.GetLogger(ctx).Debugf(
 		"QueryKeyChanges request p=%d,off=%d,to=%d response p=%d off=%d uids=%v",
 		partition, offset, toOffset, queryRes.Partition, queryRes.Offset, queryRes.UserIDs,
@@ -217,6 +219,31 @@ func TrackChangedUsers(
 	return changed, left, nil
 }
 
+func filterSharedUsers(
+	ctx context.Context, stateAPI currentstateAPI.CurrentStateInternalAPI, userID string, usersWithChangedKeys []string,
+) []string {
+	var result []string
+	var sharedUsersRes currentstateAPI.QuerySharedUsersResponse
+	err := stateAPI.QuerySharedUsers(ctx, &currentstateAPI.QuerySharedUsersRequest{
+		UserID: userID,
+	}, &sharedUsersRes)
+	if err != nil {
+		// default to all users so we do needless queries rather than miss some important device update
+		return usersWithChangedKeys
+	}
+	// We forcibly put ourselves in this list because we should be notified about our own device updates
+	// and if we are in 0 rooms then we don't technically share any room with ourselves so we wouldn't
+	// be notified about key changes.
+	sharedUsersRes.UserIDsToCount[userID] = 1
+
+	for _, uid := range usersWithChangedKeys {
+		if sharedUsersRes.UserIDsToCount[uid] > 0 {
+			result = append(result, uid)
+		}
+	}
+	return result
+}
+
 func joinedRooms(res *types.Response, userID string) []string {
 	var roomIDs []string
 	for roomID, join := range res.Rooms.Join {

sytest-whitelist

@@ -138,7 +138,7 @@ Users receive device_list updates for their own devices
 Get left notifs for other users in sync and /keys/changes when user leaves
 Local device key changes get to remote servers
 Local device key changes get to remote servers with correct prev_id
-#Server correctly handles incoming m.device_list_update
+Server correctly handles incoming m.device_list_update
 Can add account data
 Can add account data to room
 Can get account data without syncing

userapi/internal/api.go

@@ -31,6 +31,7 @@ import (
 	"github.com/matrix-org/dendrite/userapi/storage/devices"
 	"github.com/matrix-org/gomatrixserverlib"
 	"github.com/matrix-org/util"
+	"github.com/sirupsen/logrus"
 )
 
 type UserInternalAPI struct {
@@ -98,6 +99,11 @@ func (a *UserInternalAPI) PerformAccountCreation(ctx context.Context, req *api.P
 	return nil
 }
 func (a *UserInternalAPI) PerformDeviceCreation(ctx context.Context, req *api.PerformDeviceCreationRequest, res *api.PerformDeviceCreationResponse) error {
+	util.GetLogger(ctx).WithFields(logrus.Fields{
+		"localpart":    req.Localpart,
+		"device_id":    req.DeviceID,
+		"display_name": req.DeviceDisplayName,
+	}).Info("PerformDeviceCreation")
 	dev, err := a.DeviceDB.CreateDevice(ctx, req.Localpart, req.DeviceID, req.AccessToken, req.DeviceDisplayName)
 	if err != nil {
 		return err