Add image stream error handling mechanism (#18424)

packages/flutter/lib/src/widgets/image.dart

@@ -55,7 +55,7 @@ ImageConfiguration createLocalImageConfiguration(BuildContext context, { Size si
 /// Prefetches an image into the image cache.
 ///
 /// Returns a [Future] that will complete when the first image yielded by the
-/// [ImageProvider] is available.
+/// [ImageProvider] is available or failed to load.
 ///
 /// If the image is later used by an [Image] or [BoxDecoration] or [FadeInImage],
 /// it will probably be loaded faster. The consumer of the image does not need
@@ -65,17 +65,38 @@ ImageConfiguration createLocalImageConfiguration(BuildContext context, { Size si
 /// The [BuildContext] and [Size] are used to select an image configuration
 /// (see [createLocalImageConfiguration]).
 ///
+/// The `onError` argument can be used to manually handle errors while precaching.
+///
 /// See also:
 ///
 ///   * [ImageCache], which holds images that may be reused.
-Future<Null> precacheImage(ImageProvider provider, BuildContext context, { Size size }) {
+Future<Null> precacheImage(
+  ImageProvider provider,
+  BuildContext context, {
+  Size size,
+  ImageErrorListener onError,
+}) {
   final ImageConfiguration config = createLocalImageConfiguration(context, size: size);
   final Completer<Null> completer = new Completer<Null>();
   final ImageStream stream = provider.resolve(config);
   void listener(ImageInfo image, bool sync) {
     completer.complete();
   }
-  stream.addListener(listener);
+  void errorListener(dynamic exception, StackTrace stackTrace) {
+    completer.complete();
+    if (onError != null) {
+      onError(exception, stackTrace);
+    } else {
+      FlutterError.reportError(new FlutterErrorDetails(
+        context: 'image failed to precache',
+        library: 'image resource service',
+        exception: exception,
+        stack: stackTrace,
+        silent: true,
+      ));
+    }
+  }
+  stream.addListener(listener, onError: errorListener);
   completer.future.then((Null _) { stream.removeListener(listener); });
   return completer.future;
 }

packages/flutter/test/painting/image_stream_test.dart

@@ -433,6 +433,40 @@ void main() {
     expect(mockCodec.numFramesAsked, 2);
     await tester.pump(const Duration(milliseconds: 200)); // emit 2nd frame.
     expect(mockCodec.numFramesAsked, 3);
+  });
+
+  testWidgets('error handlers can intercept errors', (WidgetTester tester) async {
+    final MockCodec mockCodec = new MockCodec();
+    mockCodec.frameCount = 1;
+    final Completer<Codec> codecCompleter = new Completer<Codec>();
+
+    final ImageStreamCompleter streamUnderTest = new MultiFrameImageStreamCompleter(
+      codec: codecCompleter.future,
+      scale: 1.0,
+    );
+
+    dynamic capturedException;
+    final ImageErrorListener errorListener = (dynamic exception, StackTrace stackTrace) {
+      capturedException = exception;
+    };
+
+    streamUnderTest.addListener(
+      (ImageInfo image, bool synchronousCall) {},
+      onError: errorListener,
+    );
+
+    codecCompleter.complete(mockCodec);
+    // MultiFrameImageStreamCompleter only sets an error handler for the next
+    // frame future after the codec future has completed.
+    // Idling here lets the MultiFrameImageStreamCompleter advance and set the
+    // error handler for the nextFrame future.
+    await tester.idle();
+
+    mockCodec.failNextFrame('frame completion error');
+    await tester.idle();
 
+    // No exception is passed up.
+    expect(tester.takeException(), isNull);
+    expect(capturedException, 'frame completion error');
   });
 }