Reject make_join when no room members are left

federationapi/routing/join.go

@@ -79,6 +79,23 @@ func MakeJoin(
 		}
 	}
 
+	// Check if we think we are still joined to the room
+	inRoomReq := &api.QueryServerJoinedToRoomRequest{
+		ServerName: cfg.Matrix.ServerName,
+		RoomID:     roomID,
+	}
+	inRoomRes := &api.QueryServerJoinedToRoomResponse{}
+	if err = rsAPI.QueryServerJoinedToRoom(httpReq.Context(), inRoomReq, inRoomRes); err != nil {
+		util.GetLogger(httpReq.Context()).WithError(err).Error("rsAPI.QueryServerJoinedToRoom failed")
+		return jsonerror.InternalServerError()
+	}
+	if !inRoomRes.IsInRoom {
+		return util.JSONResponse{
+			Code: http.StatusNotFound,
+			JSON: jsonerror.NotFound("There are no remaining users in this room"),
+		}
+	}
+
 	// Try building an event for the server
 	builder := gomatrixserverlib.EventBuilder{
 		Sender:   userID,

federationapi/routing/send_test.go

@@ -199,6 +199,15 @@ func (t *testRoomserverAPI) QueryMembershipsForRoom(
 	return fmt.Errorf("not implemented")
 }
 
+// Query if a server is joined to a room
+func (t *testRoomserverAPI) QueryServerJoinedToRoom(
+	ctx context.Context,
+	request *api.QueryServerJoinedToRoomRequest,
+	response *api.QueryServerJoinedToRoomResponse,
+) error {
+	return fmt.Errorf("not implemented")
+}
+
 // Query whether a server is allowed to see an event
 func (t *testRoomserverAPI) QueryServerAllowedToSeeEvent(
 	ctx context.Context,

go.mod

@@ -22,7 +22,7 @@ require (
 	github.com/matrix-org/go-http-js-libp2p v0.0.0-20200518170932-783164aeeda4
 	github.com/matrix-org/go-sqlite3-js v0.0.0-20200522092705-bc8506ccbcf3
 	github.com/matrix-org/gomatrix v0.0.0-20200827122206-7dd5e2a05bcd
-	github.com/matrix-org/gomatrixserverlib v0.0.0-20200924092535-0404770f91c7
+	github.com/matrix-org/gomatrixserverlib v0.0.0-20200923114637-d0bf7a3c8b02
 	github.com/matrix-org/naffka v0.0.0-20200901083833-bcdd62999a91
 	github.com/matrix-org/util v0.0.0-20200807132607-55161520e1d4
 	github.com/mattn/go-sqlite3 v1.14.2

go.sum

@@ -569,8 +569,8 @@ github.com/matrix-org/gomatrix v0.0.0-20190528120928-7df988a63f26 h1:Hr3zjRsq2bh
 github.com/matrix-org/gomatrix v0.0.0-20190528120928-7df988a63f26/go.mod h1:3fxX6gUjWyI/2Bt7J1OLhpCzOfO/bB3AiX0cJtEKud0=
 github.com/matrix-org/gomatrix v0.0.0-20200827122206-7dd5e2a05bcd h1:xVrqJK3xHREMNjwjljkAUaadalWc0rRbmVuQatzmgwg=
 github.com/matrix-org/gomatrix v0.0.0-20200827122206-7dd5e2a05bcd/go.mod h1:/gBX06Kw0exX1HrwmoBibFA98yBk/jxKpGVeyQbff+s=
-github.com/matrix-org/gomatrixserverlib v0.0.0-20200924092535-0404770f91c7 h1:bTPIIp0PEOq09pLj4diAXPgW8dCbXLE5gxJ/ex9MqEc=
-github.com/matrix-org/gomatrixserverlib v0.0.0-20200924092535-0404770f91c7/go.mod h1:JsAzE1Ll3+gDWS9JSUHPJiiyAksvOOnGWF2nXdg4ZzU=
+github.com/matrix-org/gomatrixserverlib v0.0.0-20200923114637-d0bf7a3c8b02 h1:oos5KSWybuqmDKsiedQYBPFTzLLYaI3m2iisL0wB4yw=
+github.com/matrix-org/gomatrixserverlib v0.0.0-20200923114637-d0bf7a3c8b02/go.mod h1:JsAzE1Ll3+gDWS9JSUHPJiiyAksvOOnGWF2nXdg4ZzU=
 github.com/matrix-org/naffka v0.0.0-20200901083833-bcdd62999a91 h1:HJ6U3S3ljJqNffYMcIeAncp5qT/i+ZMiJ2JC2F0aXP4=
 github.com/matrix-org/naffka v0.0.0-20200901083833-bcdd62999a91/go.mod h1:sjyPyRxKM5uw1nD2cJ6O2OxI6GOqyVBfNXqKjBZTBZE=
 github.com/matrix-org/util v0.0.0-20190711121626-527ce5ddefc7 h1:ntrLa/8xVzeSs8vHFHK25k0C+NV74sYMJnNSg5NoSRo=

roomserver/api/api.go

@@ -89,6 +89,13 @@ type RoomserverInternalAPI interface {
 		response *QueryMembershipsForRoomResponse,
 	) error
 
+	// Query if we think we're still in a room.
+	QueryServerJoinedToRoom(
+		ctx context.Context,
+		request *QueryServerJoinedToRoomRequest,
+		response *QueryServerJoinedToRoomResponse,
+	) error
+
 	// Query whether a server is allowed to see an event
 	QueryServerAllowedToSeeEvent(
 		ctx context.Context,

roomserver/api/api_trace.go

@@ -134,6 +134,16 @@ func (t *RoomserverInternalAPITrace) QueryMembershipsForRoom(
 	return err
 }
 
+func (t *RoomserverInternalAPITrace) QueryServerJoinedToRoom(
+	ctx context.Context,
+	req *QueryServerJoinedToRoomRequest,
+	res *QueryServerJoinedToRoomResponse,
+) error {
+	err := t.Impl.QueryServerJoinedToRoom(ctx, req, res)
+	util.GetLogger(ctx).WithError(err).Infof("QueryServerJoinedToRoom req=%+v res=%+v", js(req), js(res))
+	return err
+}
+
 func (t *RoomserverInternalAPITrace) QueryServerAllowedToSeeEvent(
 	ctx context.Context,
 	req *QueryServerAllowedToSeeEventRequest,

roomserver/api/query.go

@@ -140,6 +140,20 @@ type QueryMembershipsForRoomResponse struct {
 	HasBeenInRoom bool `json:"has_been_in_room"`
 }
 
+// QueryServerJoinedToRoomRequest is a request to QueryServerJoinedToRoom
+type QueryServerJoinedToRoomRequest struct {
+	// Server name of the server to find
+	ServerName gomatrixserverlib.ServerName `json:"server_name"`
+	// ID of the room to see if we are still joined to
+	RoomID string `json:"room_id"`
+}
+
+// QueryMembershipsForRoomResponse is a response to QueryServerJoinedToRoom
+type QueryServerJoinedToRoomResponse struct {
+	// True if we still believe that we are participating in the room
+	IsInRoom bool `json:"is_in_room"`
+}
+
 // QueryServerAllowedToSeeEventRequest is a request to QueryServerAllowedToSeeEvent
 type QueryServerAllowedToSeeEventRequest struct {
 	// The event ID to look up invites in.

roomserver/internal/query/query.go

@@ -227,6 +227,49 @@ func (r *Queryer) QueryMembershipsForRoom(
 	return nil
 }
 
+// QueryServerJoinedToRoom implements api.RoomserverInternalAPI
+func (r *Queryer) QueryServerJoinedToRoom(
+	ctx context.Context,
+	request *api.QueryServerJoinedToRoomRequest,
+	response *api.QueryServerJoinedToRoomResponse,
+) error {
+	info, err := r.DB.RoomInfo(ctx, request.RoomID)
+	if err != nil {
+		return fmt.Errorf("r.DB.RoomInfo: %w", err)
+	}
+	if info == nil {
+		return nil
+	}
+
+	eventNIDs, err := r.DB.GetMembershipEventNIDsForRoom(ctx, info.RoomNID, true, false)
+	if err != nil {
+		return fmt.Errorf("r.DB.GetMembershipEventNIDsForRoom: %w", err)
+	}
+	if len(eventNIDs) == 0 {
+		return nil
+	}
+
+	events, err := r.DB.Events(ctx, eventNIDs)
+	if err != nil {
+		return fmt.Errorf("r.DB.Events: %w", err)
+	}
+
+	for _, e := range events {
+		if e.Type() == gomatrixserverlib.MRoomMember && e.StateKey() != nil {
+			_, serverName, err := gomatrixserverlib.SplitID('@', *e.StateKey())
+			if err != nil {
+				continue
+			}
+			if serverName == request.ServerName {
+				response.IsInRoom = true
+				break
+			}
+		}
+	}
+
+	return nil
+}
+
 // QueryServerAllowedToSeeEvent implements api.RoomserverInternalAPI
 func (r *Queryer) QueryServerAllowedToSeeEvent(
 	ctx context.Context,

roomserver/inthttp/client.go

@@ -38,6 +38,7 @@ const (
 	RoomserverQueryEventsByIDPath              = "/roomserver/queryEventsByID"
 	RoomserverQueryMembershipForUserPath       = "/roomserver/queryMembershipForUser"
 	RoomserverQueryMembershipsForRoomPath      = "/roomserver/queryMembershipsForRoom"
+	RoomserverQueryServerJoinedToRoomPath      = "/roomserver/queryServerJoinedToRoomPath"
 	RoomserverQueryServerAllowedToSeeEventPath = "/roomserver/queryServerAllowedToSeeEvent"
 	RoomserverQueryMissingEventsPath           = "/roomserver/queryMissingEvents"
 	RoomserverQueryStateAndAuthChainPath       = "/roomserver/queryStateAndAuthChain"
@@ -312,6 +313,19 @@ func (h *httpRoomserverInternalAPI) QueryMembershipsForRoom(
 	return httputil.PostJSON(ctx, span, h.httpClient, apiURL, request, response)
 }
 
+// QueryMembershipsForRoom implements RoomserverQueryAPI
+func (h *httpRoomserverInternalAPI) QueryServerJoinedToRoom(
+	ctx context.Context,
+	request *api.QueryServerJoinedToRoomRequest,
+	response *api.QueryServerJoinedToRoomResponse,
+) error {
+	span, ctx := opentracing.StartSpanFromContext(ctx, "QueryServerJoinedToRoom")
+	defer span.Finish()
+
+	apiURL := h.roomserverURL + RoomserverQueryServerJoinedToRoomPath
+	return httputil.PostJSON(ctx, span, h.httpClient, apiURL, request, response)
+}
+
 // QueryServerAllowedToSeeEvent implements RoomserverQueryAPI
 func (h *httpRoomserverInternalAPI) QueryServerAllowedToSeeEvent(
 	ctx context.Context,

roomserver/inthttp/server.go

@@ -167,6 +167,20 @@ func AddRoutes(r api.RoomserverInternalAPI, internalAPIMux *mux.Router) {
 			return util.JSONResponse{Code: http.StatusOK, JSON: &response}
 		}),
 	)
+	internalAPIMux.Handle(
+		RoomserverQueryServerJoinedToRoomPath,
+		httputil.MakeInternalAPI("queryServerJoinedToRoom", func(req *http.Request) util.JSONResponse {
+			var request api.QueryServerJoinedToRoomRequest
+			var response api.QueryServerJoinedToRoomResponse
+			if err := json.NewDecoder(req.Body).Decode(&request); err != nil {
+				return util.ErrorResponse(err)
+			}
+			if err := r.QueryServerJoinedToRoom(req.Context(), &request, &response); err != nil {
+				return util.ErrorResponse(err)
+			}
+			return util.JSONResponse{Code: http.StatusOK, JSON: &response}
+		}),
+	)
 	internalAPIMux.Handle(
 		RoomserverQueryServerAllowedToSeeEventPath,
 		httputil.MakeInternalAPI("queryServerAllowedToSeeEvent", func(req *http.Request) util.JSONResponse {

sytest-whitelist

@@ -477,3 +477,4 @@ Inbound federation correctly soft fails events
 Inbound federation accepts a second soft-failed event
 Federation key API can act as a notary server via a POST request
 Federation key API can act as a notary server via a GET request
+Inbound /make_join rejects attempts to join rooms where all users have left