screencastService: Signal errors via the internal dbus interface

Make sure gnome-shell gets notified of errors that happen during screen
recording using the screencastService, so that it can properly notify the
user about the error and tear down its state, too.

Part-of: <https://gitlab.gnome.org/GNOME/gnome-shell/-/merge_requests/2752>

data/dbus-interfaces/org.gnome.Shell.Screencast.xml

@@ -92,5 +92,9 @@
       <arg type="b" direction="out" name="success"/>
     </method>
 
+    <signal name="Error">
+      <arg type="s" name="message"/>
+    </signal>
+
   </interface>
 </node>

js/dbusServices/org.gnome.Shell.Screencast.src.gresource.xml

@@ -7,5 +7,7 @@
 
     <file>misc/config.js</file>
     <file>misc/dbusUtils.js</file>
+    <file>misc/signals.js</file>
+    <file>misc/signalTracker.js</file>
   </gresource>
 </gresources>

js/dbusServices/screencast/screencastService.js

@@ -7,6 +7,7 @@ imports.gi.versions.Gtk = '4.0';
 const { Gio, GLib, Gst, Gtk } = imports.gi;
 
 const { loadInterfaceXML, loadSubInterfaceXML } = imports.misc.dbusUtils;
+const Signals = imports.misc.signals;
 const { ServiceImplementation } = imports.dbusService;
 
 const ScreencastIface = loadInterfaceXML('org.gnome.Shell.Screencast');
@@ -54,13 +55,13 @@ const SessionState = {
     STOPPED: 'STOPPED',
 };
 
-var Recorder = class {
+var Recorder = class extends Signals.EventEmitter {
     constructor(sessionPath, x, y, width, height, filePath, options,
-        invocation,
+        invocation) {
-        onErrorCallback) {
+        super();
+
         this._startInvocation = invocation;
         this._dbusConnection = invocation.get_connection();
-        this._onErrorCallback = onErrorCallback;
         this._stopInvocation = null;
 
         this._x = x;
@@ -147,11 +148,6 @@ var Recorder = class {
 
         log(`Recorder error: ${error.message}`);
 
-        if (this._onErrorCallback) {
-            this._onErrorCallback();
-            delete this._onErrorCallback;
-        }
-
         if (this._startRequest) {
             this._startRequest.reject(error);
             delete this._startRequest;
@@ -161,6 +157,8 @@ var Recorder = class {
             this._stopRequest.reject(error);
             delete this._stopRequest;
         }
+
+        this.emit('error', error);
     }
 
     _handleFatalPipelineError(message) {
@@ -529,8 +527,7 @@ var ScreencastService = class extends ServiceImplementation {
                 screenWidth, screenHeight,
                 filePath,
                 options,
-                invocation,
+                invocation);
-                () => this._removeRecorder(sender));
         } catch (error) {
             log(`Failed to create recorder: ${error.message}`);
             invocation.return_value(GLib.Variant.new('(bs)', returnValue));
@@ -548,6 +545,12 @@ var ScreencastService = class extends ServiceImplementation {
         } finally {
             invocation.return_value(GLib.Variant.new('(bs)', returnValue));
         }
+
+        recorder.connect('error', (r, error) => {
+            this._removeRecorder(sender);
+            this._dbusImpl.emit_signal('Error',
+                new GLib.Variant('(s)', [error.message]));
+        });
     }
 
     async ScreencastAreaAsync(params, invocation) {
@@ -579,8 +582,7 @@ var ScreencastService = class extends ServiceImplementation {
                 width, height,
                 filePath,
                 options,
-                invocation,
+                invocation);
-                () => this._removeRecorder(sender));
         } catch (error) {
             log(`Failed to create recorder: ${error.message}`);
             invocation.return_value(GLib.Variant.new('(bs)', returnValue));
@@ -598,6 +600,12 @@ var ScreencastService = class extends ServiceImplementation {
         } finally {
             invocation.return_value(GLib.Variant.new('(bs)', returnValue));
         }
+
+        recorder.connect('error', (r, error) => {
+            this._removeRecorder(sender);
+            this._dbusImpl.emit_signal('Error',
+                new GLib.Variant('(s)', [error.message]));
+        });
     }
 
     async StopScreencastAsync(params, invocation) {