fix: handle screenshare failure gracefully

Author: coder-with-a-bushido

lib/src/voip/call_session.dart

@@ -592,7 +592,6 @@ class CallSession {
         await addLocalStream(stream, SDPStreamMetadataPurpose.Screenshare);
         return true;
       } catch (err) {
-        fireCallEvent(CallStateChange.kError);
         return false;
       }
     } else {
@@ -1315,16 +1314,16 @@ class CallSession {
       return await voip.delegate.mediaDevices.getUserMedia(mediaConstraints);
     } catch (e) {
       await _getUserMediaFailed(e);
-      rethrow;
     }
+    return null;
   }
 
   Future<MediaStream?> _getDisplayMedia() async {
     try {
       return await voip.delegate.mediaDevices
           .getDisplayMedia(UserMediaConstraints.screenMediaConstraints);
     } catch (e) {
-      await _getUserMediaFailed(e);
+      await _getDisplayMediaFailed(e);
     }
     return null;
   }
@@ -1493,6 +1492,18 @@ class CallSession {
     );
   }
 
+  Future<void> _getDisplayMediaFailed(dynamic err) async {
+    Logs().w('Failed to get display media - ending call ${err.toString()}');
+    fireCallEvent(CallStateChange.kError);
+    // We don't terminate the call here because the user might still want to stay
+    // on the call and try again later.
+    throw CallError(
+      CallErrorCode.displayMediaFailed,
+      'Failed to get display media',
+      err,
+    );
+  }
+
   Future<void> onSelectAnswerReceived(String? selectedPartyId) async {
     if (direction != CallDirection.kIncoming) {
       Logs().w('Got select_answer for an outbound call: ignoring');

lib/src/voip/utils/types.dart

@@ -50,6 +50,11 @@ enum CallErrorCode {
   /// the hardware isn't plugged in, or the user has explicitly denied access.
   userMediaFailed('user_media_failed'),
 
+  /// An error code when there is no local display to screenshare. This may be
+  /// because the hardware isn't plugged in, or the user has explicitly denied
+  /// access.
+  displayMediaFailed('display_media_failed'),
+
   /// Error code used when a call event failed to send
   /// because unknown devices were present in the room
   unknownDevice('unknown_device'),

test/calls_test.dart

@@ -635,6 +635,32 @@ void main() {
       }
     });
 
+    test('Call continues when getDisplayMedia fails', () async {
+      final mockDelegate = MockWebRTCDelegate();
+      mockDelegate.mediaDevices.throwOnGetDisplayMedia = true;
+      voip = VoIP(matrix, mockDelegate);
+      VoIP.customTxid = '1234';
+
+      final call = await voip.inviteToCall(
+        room,
+        CallType.kVoice,
+        userId: '@alice:testing.com',
+      );
+
+      // Attempt to share screen - should not throw or terminate call
+      try {
+        await call.setScreensharingEnabled(true);
+      } catch (e) {
+        fail('Screen sharing failure should be handled internally');
+      }
+
+      expect(call.onCallEventChanged.value, CallStateChange.kError);
+      expect(call.state, isNot(CallState.kEnded));
+      expect(voip.currentCID, isNotNull);
+
+      await call.hangup(reason: CallErrorCode.userHangup);
+    });
+
     test('getFamedlyCallEvents sort order', () {
       room.setState(
         Event(

test/webrtc_stub.dart

@@ -54,8 +54,10 @@ class MockWebRTCDelegate implements WebRTCDelegate {
   @override
   bool get isWeb => false;
 
+  final _mockMediaDevices = MockMediaDevices();
+
   @override
-  MediaDevices get mediaDevices => MockMediaDevices();
+  MockMediaDevices get mediaDevices => _mockMediaDevices;
 
   @override
   Future<void> playRingtone() async {
@@ -93,6 +95,8 @@ class MockEncryptionKeyProvider implements EncryptionKeyProvider {
 }
 
 class MockMediaDevices implements MediaDevices {
+  bool throwOnGetDisplayMedia = false;
+
   @override
   Function(dynamic event)? ondevicechange;
 
@@ -102,8 +106,13 @@ class MockMediaDevices implements MediaDevices {
   }
 
   @override
-  Future<MediaStream> getDisplayMedia(Map<String, dynamic> mediaConstraints) {
-    throw UnimplementedError();
+  Future<MediaStream> getDisplayMedia(
+    Map<String, dynamic> mediaConstraints,
+  ) async {
+    if (throwOnGetDisplayMedia) {
+      throw Exception('mock exception while getting display media');
+    }
+    return MockMediaStream('', '');
   }
 
   @override