fix: handle cancellation in image loading and simplify request assignment

mobile/lib/domain/models/config/image_config.dart

@@ -1,20 +1,28 @@
 class ImageConfig {
   final bool preferRemote;
+  final bool loadPreview;
   final bool loadOriginal;
 
-  const ImageConfig({this.preferRemote = false, this.loadOriginal = false});
+  const ImageConfig({this.preferRemote = false, this.loadPreview = true, this.loadOriginal = false});
 
-  ImageConfig copyWith({bool? preferRemote, bool? loadOriginal}) =>
-      ImageConfig(preferRemote: preferRemote ?? this.preferRemote, loadOriginal: loadOriginal ?? this.loadOriginal);
+  ImageConfig copyWith({bool? preferRemote, bool? loadPreview, bool? loadOriginal}) => ImageConfig(
+    preferRemote: preferRemote ?? this.preferRemote,
+    loadPreview: loadPreview ?? this.loadPreview,
+    loadOriginal: loadOriginal ?? this.loadOriginal,
+  );
 
   @override
   bool operator ==(Object other) =>
       identical(this, other) ||
-      (other is ImageConfig && other.preferRemote == preferRemote && other.loadOriginal == loadOriginal);
+      (other is ImageConfig &&
+          other.preferRemote == preferRemote &&
+          other.loadPreview == loadPreview &&
+          other.loadOriginal == loadOriginal);
 
   @override
-  int get hashCode => Object.hash(preferRemote, loadOriginal);
+  int get hashCode => Object.hash(preferRemote, loadPreview, loadOriginal);
 
   @override
-  String toString() => 'ImageConfig(preferRemoteImage: $preferRemote, loadOriginal: $loadOriginal)';
+  String toString() =>
+      'ImageConfig(preferRemoteImage: $preferRemote, loadPreview: $loadPreview, loadOriginal: $loadOriginal)';
 }

mobile/lib/domain/models/metadata_key.dart

@@ -27,6 +27,7 @@ enum MetadataKey<T extends Object> {
 
   // Image
   imagePreferRemote<bool>(.appConfig, 'image.preferRemote', false),
+  imageLoadPreview<bool>(.appConfig, 'image.loadPreview', true),
   imageLoadOriginal<bool>(.appConfig, 'image.loadOriginal', false),
 
   // Viewer

mobile/lib/infrastructure/repositories/metadata.repository.dart

@@ -133,7 +133,11 @@ extension<T extends Object> on MetadataDomain<T> {
             groupAssetsBy: repo._read(.timelineGroupAssetsBy),
             storageIndicator: repo._read(.timelineStorageIndicator),
           ),
-          image: .new(preferRemote: repo._read(.imagePreferRemote), loadOriginal: repo._read(.imageLoadOriginal)),
+          image: .new(
+            preferRemote: repo._read(.imagePreferRemote),
+            loadPreview: repo._read(.imageLoadPreview),
+            loadOriginal: repo._read(.imageLoadOriginal),
+          ),
           viewer: .new(
             loopVideo: repo._read(.viewerLoopVideo),
             loadOriginalVideo: repo._read(.viewerLoadOriginalVideo),

mobile/lib/presentation/widgets/images/image_provider.dart

@@ -44,7 +44,6 @@ mixin CancellableImageProviderMixin<T extends Object> on CancellableImageProvide
 
     completer.operation.valueOrCancellation().whenComplete(() {
       cachedStream.removeListener(listener);
-      cachedOperation = null;
     });
     cachedOperation = completer.operation;
     return null;
@@ -94,6 +93,9 @@ mixin CancellableImageProviderMixin<T extends Object> on CancellableImageProvide
       isFinished = isFinal;
       return codec;
     } catch (e) {
+      if (isCancelled) {
+        return null;
+      }
       if (isFinal) {
         isFinished = true;
         PaintingBinding.instance.imageCache.evict(this);
@@ -105,18 +107,33 @@ mixin CancellableImageProviderMixin<T extends Object> on CancellableImageProvide
     }
   }
 
-  Stream<ImageInfo> initialImageStream() async* {
+  Stream<ImageInfo> initialImageStream({required bool isFinal}) async* {
     final cachedOperation = this.cachedOperation;
+    if (isCancelled) {
+      return;
+    }
     if (cachedOperation == null) {
+      // image resolved synchronously
+      isFinished = isFinal;
       return;
     }
 
     try {
       final cachedImage = await cachedOperation.valueOrCancellation();
-      if (cachedImage != null && !isCancelled) {
-        yield cachedImage;
+      if (isCancelled || cachedImage == null) {
+        return;
       }
+      isFinished = isFinal;
+      yield cachedImage;
     } catch (e, stack) {
+      if (isCancelled) {
+        return;
+      }
+      if (isFinal) {
+        isFinished = true;
+        PaintingBinding.instance.imageCache.evict(this);
+        rethrow;
+      }
       _log.severe('Error loading initial image', e, stack);
     } finally {
       this.cachedOperation = null;

mobile/lib/presentation/widgets/images/local_image_provider.dart

@@ -98,51 +98,55 @@ class LocalFullImageProvider extends CancellableImageProvider<LocalFullImageProv
   }
 
   Stream<ImageInfo> _codec(LocalFullImageProvider key, ImageDecoderCallback decode) async* {
-    yield* initialImageStream();
+    final loadOriginal = MetadataRepository.instance.appConfig.image.loadOriginal;
+    final loadPreview = MetadataRepository.instance.appConfig.image.loadPreview;
+    yield* initialImageStream(isFinal: !loadOriginal && !loadPreview);
 
     if (isCancelled) {
       return;
     }
 
-    final loadOriginal = MetadataRepository.instance.appConfig.image.loadOriginal;
-    final devicePixelRatio = PlatformDispatcher.instance.views.first.devicePixelRatio;
-    var request = this.request = LocalImageRequest(
-      localId: key.id,
-      size: Size(size.width * devicePixelRatio, size.height * devicePixelRatio),
-      assetType: key.assetType,
-    );
-    yield* loadRequest(request, decode, isFinal: !loadOriginal);
+    if (loadPreview) {
+      final devicePixelRatio = PlatformDispatcher.instance.views.first.devicePixelRatio;
+      final previewRequest = request = LocalImageRequest(
+        localId: key.id,
+        size: Size(size.width * devicePixelRatio, size.height * devicePixelRatio),
+        assetType: key.assetType,
+      );
+      yield* loadRequest(previewRequest, decode, isFinal: !loadOriginal);
+
+      if (isCancelled) {
+        return;
+      }
+    }
 
     if (!loadOriginal) {
       return;
     }
 
-    if (isCancelled) {
-      return;
-    }
-
-    request = this.request = LocalImageRequest(localId: key.id, assetType: key.assetType, size: Size.zero);
-
-    yield* loadRequest(request, decode, isFinal: true);
+    final originalRequest = request = LocalImageRequest(localId: key.id, assetType: key.assetType, size: Size.zero);
+    yield* loadRequest(originalRequest, decode, isFinal: true);
   }
 
   Stream<Object> _animatedCodec(LocalFullImageProvider key, ImageDecoderCallback decode) async* {
-    yield* initialImageStream();
+    yield* initialImageStream(isFinal: false);
 
     if (isCancelled) {
       return;
     }
 
-    final devicePixelRatio = PlatformDispatcher.instance.views.first.devicePixelRatio;
-    final previewRequest = request = LocalImageRequest(
-      localId: key.id,
-      size: Size(size.width * devicePixelRatio, size.height * devicePixelRatio),
-      assetType: key.assetType,
-    );
-    yield* loadRequest(previewRequest, decode, isFinal: false);
+    if (MetadataRepository.instance.appConfig.image.loadPreview) {
+      final devicePixelRatio = PlatformDispatcher.instance.views.first.devicePixelRatio;
+      final previewRequest = request = LocalImageRequest(
+        localId: key.id,
+        size: Size(size.width * devicePixelRatio, size.height * devicePixelRatio),
+        assetType: key.assetType,
+      );
+      yield* loadRequest(previewRequest, decode, isFinal: false);
 
-    if (isCancelled) {
-      return;
+      if (isCancelled) {
+        return;
+      }
     }
 
     // always try original for animated, since previews don't support animation

mobile/lib/presentation/widgets/images/remote_image_provider.dart

@@ -108,31 +108,35 @@ class RemoteFullImageProvider extends CancellableImageProvider<RemoteFullImagePr
   }
 
   Stream<ImageInfo> _codec(RemoteFullImageProvider key, ImageDecoderCallback decode) async* {
-    yield* initialImageStream();
+    final isImage = assetType == AssetType.image;
+    final loadOriginal = isImage && MetadataRepository.instance.appConfig.image.loadOriginal;
+    final loadPreview = isImage && MetadataRepository.instance.appConfig.image.loadPreview;
+    yield* initialImageStream(isFinal: !loadOriginal && !loadPreview);
 
     if (isCancelled) {
       return;
     }
 
-    final previewRequest = request = RemoteImageRequest(
-      uri: getThumbnailUrlForRemoteId(
-        key.assetId,
-        type: AssetMediaSize.preview,
-        thumbhash: key.thumbhash,
-        edited: key.edited,
-      ),
-    );
-    final loadOriginal = assetType == AssetType.image && MetadataRepository.instance.appConfig.image.loadOriginal;
-    yield* loadRequest(previewRequest, decode, isFinal: !loadOriginal);
+    if (loadPreview) {
+      final previewRequest = request = RemoteImageRequest(
+        uri: getThumbnailUrlForRemoteId(
+          key.assetId,
+          type: AssetMediaSize.preview,
+          thumbhash: key.thumbhash,
+          edited: key.edited,
+        ),
+      );
+      yield* loadRequest(previewRequest, decode, isFinal: !loadOriginal);
+
+      if (isCancelled) {
+        return;
+      }
+    }
 
     if (!loadOriginal) {
       return;
     }
 
-    if (isCancelled) {
-      return;
-    }
-
     final originalRequest = request = RemoteImageRequest(
       uri: getOriginalUrlForRemoteId(key.assetId, edited: key.edited),
     );
@@ -140,24 +144,26 @@ class RemoteFullImageProvider extends CancellableImageProvider<RemoteFullImagePr
   }
 
   Stream<Object> _animatedCodec(RemoteFullImageProvider key, ImageDecoderCallback decode) async* {
-    yield* initialImageStream();
+    yield* initialImageStream(isFinal: false);
 
     if (isCancelled) {
       return;
     }
 
-    final previewRequest = request = RemoteImageRequest(
-      uri: getThumbnailUrlForRemoteId(
-        key.assetId,
-        type: AssetMediaSize.preview,
-        thumbhash: key.thumbhash,
-        edited: key.edited,
-      ),
-    );
-    yield* loadRequest(previewRequest, decode, isFinal: false);
+    if (MetadataRepository.instance.appConfig.image.loadPreview) {
+      final previewRequest = request = RemoteImageRequest(
+        uri: getThumbnailUrlForRemoteId(
+          key.assetId,
+          type: AssetMediaSize.preview,
+          thumbhash: key.thumbhash,
+          edited: key.edited,
+        ),
+      );
+      yield* loadRequest(previewRequest, decode, isFinal: false);
 
-    if (isCancelled) {
-      return;
+      if (isCancelled) {
+        return;
+      }
     }
 
     // always try original for animated, since previews don't support animation

mobile/lib/widgets/settings/asset_viewer_settings/image_viewer_quality_setting.dart

@@ -12,7 +12,11 @@ class ImageViewerQualitySetting extends HookConsumerWidget {
 
   @override
   Widget build(BuildContext context, WidgetRef ref) {
+    final isPreview = useState(ref.read(appConfigProvider).image.loadPreview);
     final isOriginal = useState(ref.read(appConfigProvider).image.loadOriginal);
+    useValueChanged<bool, void>(isPreview.value, (_, __) {
+      ref.read(metadataProvider).write(.imageLoadPreview, isPreview.value);
+    });
     useValueChanged<bool, void>(isOriginal.value, (_, __) {
       ref.read(metadataProvider).write(.imageLoadOriginal, isOriginal.value);
     });
@@ -25,6 +29,12 @@ class ImageViewerQualitySetting extends HookConsumerWidget {
           icon: Icons.image_outlined,
           subtitle: "setting_image_viewer_help".t(context: context),
         ),
+        SettingsSwitchListTile(
+          valueNotifier: isPreview,
+          title: "setting_image_viewer_preview_title".t(context: context),
+          subtitle: "setting_image_viewer_preview_subtitle".t(context: context),
+          onChanged: (_) => ref.invalidate(appSettingsServiceProvider),
+        ),
         SettingsSwitchListTile(
           valueNotifier: isOriginal,
           title: "setting_image_viewer_original_title".t(context: context),