Add configuration option for sliding sync when hosting /.well-known/matrix/client

clientapi/routing/routing.go

@@ -96,6 +96,33 @@ func Setup(
 
 	if cfg.Matrix.WellKnownClientName != "" {
 		logrus.Infof("Setting m.homeserver base_url as %s at /.well-known/matrix/client", cfg.Matrix.WellKnownClientName)
+		if cfg.Matrix.WellKnownSlidingSyncProxy != "" {
+			logrus.Infof("Setting org.matrix.msc3575.proxy url as %s at /.well-known/matrix/client", cfg.Matrix.WellKnownSlidingSyncProxy)
+			wkMux.Handle("/client", httputil.MakeExternalAPI("wellknown", func(r *http.Request) util.JSONResponse {
+				return util.JSONResponse{
+					Code: http.StatusOK,
+					JSON: struct {
+						HomeserverName struct {
+							BaseUrl string `json:"base_url"`
+						} `json:"m.homeserver"`
+						SlidingSyncProxy struct {
+							Url string `json:"url"`
+						} `json:"org.matrix.msc3575.proxy"`
+					}{
+						HomeserverName: struct {
+							BaseUrl string `json:"base_url"`
+						}{
+							BaseUrl: cfg.Matrix.WellKnownClientName,
+						},
+						SlidingSyncProxy: struct {
+							Url string `json:"url"`
+						}{
+							Url: cfg.Matrix.WellKnownSlidingSyncProxy,
+						},
+					},
+				}
+			})).Methods(http.MethodGet, http.MethodOptions)
+		} else {
 			wkMux.Handle("/client", httputil.MakeExternalAPI("wellknown", func(r *http.Request) util.JSONResponse {
 				return util.JSONResponse{
 					Code: http.StatusOK,
@@ -113,6 +140,7 @@ func Setup(
 				}
 			})).Methods(http.MethodGet, http.MethodOptions)
 		}
+	}
 
 	publicAPIMux.Handle("/versions",
 		httputil.MakeExternalAPI("versions", func(req *http.Request) util.JSONResponse {

setup/config/config_global.go

@@ -48,6 +48,10 @@ type Global struct {
 	// The server name to delegate client-server communications to, with optional port
 	WellKnownClientName string `yaml:"well_known_client_name"`
 
+	// The server name to delegate sliding sync communications to, with optional port.
+	// Requires `well_known_client_name` to also be configured.
+	WellKnownSlidingSyncProxy string `yaml:"well_known_sliding_sync_proxy"`
+
 	// Disables federation. Dendrite will not be able to make any outbound HTTP requests
 	// to other servers and the federation API will not be exposed.
 	DisableFederation bool `yaml:"disable_federation"`