Add admin endpoint to query empty rooms (#3663)

This is to complement the existing [Purge Room Admin
API](https://element-hq.github.io/dendrite/administration/adminapi#post-_dendriteadminpurgeroomroomid)
### Pull Request Checklist

<!-- Please read
https://matrix-org.github.io/dendrite/development/contributing before
submitting your pull request -->

* [x] I have added Go unit tests or [Complement integration
tests](https://github.com/matrix-org/complement) for this PR _or_ I have
justified why this PR doesn't need tests
* [x] Pull request includes a [sign off
below](https://element-hq.github.io/dendrite/development/contributing#sign-off)
_or_ I have already signed off privately

---------

Signed-off-by: Till Faelligen <2353100+S7evinK@users.noreply.github.com>

clientapi/routing/admin.go

@@ -73,7 +73,7 @@ func AdminCreateNewRegistrationToken(req *http.Request, cfg *config.ClientAPI, u
 	}
 
 	if len(token) > 64 {
-		//Token present in request body, but is too long.
+		// Token present in request body, but is too long.
 		return util.JSONResponse{
 			Code: http.StatusBadRequest,
 			JSON: spec.BadJSON("token must not be longer than 64"),
@@ -578,6 +578,23 @@ func DeleteEventReport(req *http.Request, rsAPI roomserverAPI.ClientRoomserverAP
 	}
 }
 
+func QueryEmptyRooms(req *http.Request, rsAPI roomserverAPI.ClientRoomserverAPI) util.JSONResponse {
+	emptyRooms, err := rsAPI.AdminQueryEmptyRooms(req.Context())
+	if err != nil {
+		logrus.WithError(err).Error("failed to query empty rooms")
+		return util.JSONResponse{
+			Code: http.StatusInternalServerError,
+			JSON: spec.InternalServerError{},
+		}
+	}
+	return util.JSONResponse{
+		Code: http.StatusOK,
+		JSON: map[string]any{
+			"empty_rooms": emptyRooms,
+		},
+	}
+}
+
 func parseUint64OrDefault(input string, defaultValue uint64) uint64 {
 	v, err := strconv.ParseUint(input, 10, 64)
 	if err != nil {

clientapi/routing/routing.go

@@ -243,6 +243,12 @@ func Setup(
 		}),
 	).Methods(http.MethodPost, http.MethodOptions)
 
+	dendriteAdminRouter.Handle("/admin/emptyRooms",
+		httputil.MakeAdminAPI("admin_empty_rooms", userAPI, func(req *http.Request, device *userapi.Device) util.JSONResponse {
+			return QueryEmptyRooms(req, rsAPI)
+		}),
+	).Methods(http.MethodGet, http.MethodOptions)
+
 	// server notifications
 	if cfg.Matrix.ServerNotices.Enabled {
 		logrus.Info("Enabling server notices at /_synapse/admin/v1/send_server_notice")

docs/administration/4_adminapi.md

@@ -77,6 +77,19 @@ This endpoint instructs Dendrite to immediately query `/devices/{userID}` on a f
 
 This endpoint instructs Dendrite to remove the given room from its database. It does **NOT** remove media files. Depending on the size of the room, this may take a while. Will return an empty JSON once other components were instructed to delete the room.
 
+## GET `/_dendrite/admin/emptyRooms`
+
+Returns a list of all rooms which have zero (locally) joined members. Response format:
+
+```json
+{
+    "empty_rooms": [
+        "!roomid1:server_name",
+        "!roomid2:server_name"
+    ]
+}
+```
+
 ## POST `/_synapse/admin/v1/send_server_notice`
 
 Request body format:

roomserver/api/api.go

@@ -89,6 +89,8 @@ type RoomserverInternalAPI interface {
 
 	// RoomsWithACLs returns all room IDs for rooms with ACLs
 	RoomsWithACLs(ctx context.Context) ([]string, error)
+	// EmptyRooms returns all rooms that the local server has left.
+	EmptyRooms(ctx context.Context) ([]string, error)
 }
 
 type UserRoomPrivateKeyCreator interface {
@@ -248,6 +250,7 @@ type ClientRoomserverAPI interface {
 	PerformAdminEvacuateUser(ctx context.Context, userID string) (affected []string, err error)
 	PerformAdminPurgeRoom(ctx context.Context, roomID string) error
 	PerformAdminDownloadState(ctx context.Context, roomID, userID string, serverName spec.ServerName) error
+	AdminQueryEmptyRooms(ctx context.Context) ([]string, error)
 	PerformPeek(ctx context.Context, req *PerformPeekRequest) (roomID string, err error)
 	PerformUnpeek(ctx context.Context, roomID, userID, deviceID string) error
 	PerformInvite(ctx context.Context, req *PerformInviteRequest) error
@@ -263,7 +266,7 @@ type ClientRoomserverAPI interface {
 	// If true, then the alias has not been set to the provided room, as it already in use.
 	SetRoomAlias(ctx context.Context, senderID spec.SenderID, roomID spec.RoomID, alias string) (aliasAlreadyExists bool, err error)
 
-	//RemoveRoomAlias(ctx context.Context, req *RemoveRoomAliasRequest, res *RemoveRoomAliasResponse) error
+	// RemoveRoomAlias(ctx context.Context, req *RemoveRoomAliasRequest, res *RemoveRoomAliasResponse) error
 	// Removes a room alias, as provided sender.
 	//
 	// Returns whether the alias was found, whether it was removed, and an error (if any occurred)

roomserver/internal/perform/perform_admin.go

@@ -350,3 +350,7 @@ func (r *Admin) PerformAdminDownloadState(
 func (r *Admin) PerformAdminDeleteEventReport(ctx context.Context, reportID uint64) error {
 	return r.DB.AdminDeleteEventReport(ctx, reportID)
 }
+
+func (r *Admin) AdminQueryEmptyRooms(ctx context.Context) ([]string, error) {
+	return r.DB.EmptyRooms(ctx)
+}

roomserver/internal/query/query.go

@@ -1097,6 +1097,11 @@ func (r *Queryer) RoomsWithACLs(ctx context.Context) ([]string, error) {
 	return r.DB.RoomsWithACLs(ctx)
 }
 
+// EmptyRooms returns all rooms that the local server has left.
+func (r *Queryer) EmptyRooms(ctx context.Context) ([]string, error) {
+	return r.DB.EmptyRooms(ctx)
+}
+
 // QueryAdminEventReports returns event reports given a filter.
 func (r *Queryer) QueryAdminEventReports(ctx context.Context, from uint64, limit uint64, backwards bool, userID, roomID string) ([]api.QueryAdminEventReportsResponse, int64, error) {
 	return r.DB.QueryAdminEventReports(ctx, from, limit, backwards, userID, roomID)

roomserver/roomserver_test.go

@@ -1319,3 +1319,35 @@ func TestRoomsWithACLs(t *testing.T) {
 		assert.Equal(t, []string{aclRoom.ID}, roomsWithACLs)
 	})
 }
+
+func TestEmptyRooms(t *testing.T) {
+	ctx := context.Background()
+	alice := test.NewUser(t)
+	r1 := test.NewRoom(t, alice)
+	r2 := test.NewRoom(t, alice)
+
+	r2.CreateAndInsert(t, alice, spec.MRoomMember, map[string]interface{}{"membership": spec.Leave}, test.WithStateKey(alice.ID))
+
+	test.WithAllDatabases(t, func(t *testing.T, dbType test.DBType) {
+		cfg, processCtx, closeDB := testrig.CreateConfig(t, dbType)
+		defer closeDB()
+
+		cm := sqlutil.NewConnectionManager(processCtx, cfg.Global.DatabaseOptions)
+		natsInstance := &jetstream.NATSInstance{}
+		caches := caching.NewRistrettoCache(128*1024*1024, time.Hour, caching.DisableMetrics)
+		// start JetStream listeners
+		rsAPI := roomserver.NewInternalAPI(processCtx, cfg, cm, natsInstance, caches, caching.DisableMetrics)
+		rsAPI.SetFederationAPI(nil, nil)
+
+		for _, room := range []*test.Room{r1, r2} {
+			// Create the rooms
+			err := api.SendEvents(ctx, rsAPI, api.KindNew, room.Events(), "test", "test", "test", nil, false)
+			assert.NoError(t, err)
+		}
+
+		// We should only have r2 as an empty room
+		emptyRooms, err := rsAPI.EmptyRooms(ctx)
+		assert.NoError(t, err)
+		assert.Equal(t, []string{r2.ID}, emptyRooms)
+	})
+}

roomserver/storage/interface.go

@@ -187,6 +187,9 @@ type Database interface {
 
 	// RoomsWithACLs returns all room IDs for rooms with ACLs
 	RoomsWithACLs(ctx context.Context) ([]string, error)
+
+	// EmptyRooms returns all rooms that the local server has left.
+	EmptyRooms(ctx context.Context) ([]string, error)
 	// GetBulkStateACLs returns all server ACLs for the given rooms.
 	GetBulkStateACLs(ctx context.Context, roomIDs []string) ([]tables.StrippedEvent, error)
 	QueryAdminEventReports(ctx context.Context, from uint64, limit uint64, backwards bool, userID string, roomID string) ([]api.QueryAdminEventReportsResponse, int64, error)

roomserver/storage/shared/storage.go

@@ -1707,6 +1707,32 @@ func (d *Database) RoomsWithACLs(ctx context.Context) ([]string, error) {
 	return roomIDs, nil
 }
 
+// EmptyRooms returns all rooms that the local server has left.
+func (d *Database) EmptyRooms(ctx context.Context) ([]string, error) {
+	eventTypeNID := types.EventTypeNID(5)
+
+	roomNIDs, err := d.EventsTable.SelectRoomsWithEventTypeNID(ctx, nil, eventTypeNID)
+	if err != nil {
+		return nil, err
+	}
+
+	// Figure out if we are joined to the rooms
+	leftRoomsNIDs := make([]types.RoomNID, 0, len(roomNIDs))
+	for i := 0; i < len(roomNIDs); i++ {
+		inRoom, err := d.GetLocalServerInRoom(ctx, roomNIDs[i])
+		if err != nil {
+			return nil, err
+		}
+		if inRoom {
+			continue
+		}
+		// Server is not in the room anymore
+		leftRoomsNIDs = append(leftRoomsNIDs, roomNIDs[i])
+	}
+
+	return d.RoomsTable.BulkSelectRoomIDs(ctx, nil, leftRoomsNIDs)
+}
+
 // ForgetRoom sets a users room to forgotten
 func (d *Database) ForgetRoom(ctx context.Context, userID, roomID string, forget bool) error {
 	roomNIDs, err := d.RoomsTable.BulkSelectRoomNIDs(ctx, nil, []string{roomID})