[image_picker_web] Listens to file input cancel event. (#4453)

## Changes

This PR listens to the `cancel` event from the `input type=file` used by the web implementation of the image_picker plugin, so apps don't end up endlessly awaiting for a file that will never come **in modern browsers** (Chrome 113, Safari 16.4, or newer). _Same API as #3683

Additionally, this PR:

* Removes all code and tests mentioning `PickedFile`. (Deprecated years ago, and unused since #4285) **(Breaking change)**
* Updates README to mention `XFile` which is the current return type of the package.
* Updates the dependency on `image_picker_platform_interface` to `^2.9.0`.
  * Implements all non-deprecated methods from the interface, and makes deprecated methods use the fresh ones.
  * Updates tests.

### Issues

* Fixes flutter/flutter#92176

### Testing

* Added integration testing coverage for the 'cancel' event.
* Tested manually in Chrome with the example app running on web.

Author: ditman

packages/image_picker/image_picker_for_web/CHANGELOG.md

@@ -1,3 +1,10 @@
+## 3.0.0
+
+* **BREAKING CHANGE:** Removes all code and tests mentioning `PickedFile`.
+* Listens to `cancel` event on file selection. When the selection is canceled:
+  * `Future<XFile?>` methods return `null`
+  * `Future<List<XFile>>` methods return an empty list.
+
 ## 2.2.0
 
 * Adds `getMedia` method.

packages/image_picker/image_picker_for_web/README.md

@@ -4,23 +4,12 @@ A web implementation of [`image_picker`][1].
 
 ## Limitations on the web platform
 
-Since Web Browsers don't offer direct access to their users' file system,
-this plugin provides a `PickedFile` abstraction to make access uniform
-across platforms.
+### `XFile`
 
-The web version of the plugin puts network-accessible URIs as the `path`
-in the returned `PickedFile`.
+This plugin uses `XFile` objects to abstract files picked/created by the user.
 
-### URL.createObjectURL()
-
-The `PickedFile` object in web is backed by [`URL.createObjectUrl` Web API](https://developer.mozilla.org/en-US/docs/Web/API/URL/createObjectURL),
-which is reasonably well supported across all browsers:
-
-![Data on support for the bloburls feature across the major browsers from caniuse.com](https://caniuse.bitsofco.de/image/bloburls.png)
-
-However, the returned `path` attribute of the `PickedFile` points to a `network` resource, and not a
-local path in your users' drive. See **Use the plugin** below for some examples on how to use this
-return value in a cross-platform way.
+Read more about `XFile` on the web in
+[`package:cross_file`'s README](https://pub.dev/packages/cross_file).
 
 ### input file "accept"
 
@@ -42,11 +31,26 @@ In order to "take a photo", some mobile browsers offer a [`capture` attribute](h
 Each browser may implement `capture` any way they please, so it may (or may not) make a
 difference in your users' experience.
 
-### pickImage()
-The arguments `maxWidth`, `maxHeight` and `imageQuality` are not supported for gif images.
-The argument `imageQuality` only works for jpeg and webp images.
+### input file "cancel"
+
+The [`cancel` event](https://caniuse.com/mdn-api_htmlinputelement_cancel_event)
+used by the plugin to detect when users close the file selector without picking
+a file is relatively new, and will only work in recent browsers.
+
+### `ImagePickerOptions` support
+
+The `ImagePickerOptions` configuration object allows passing resize (`maxWidth`,
+`maxHeight`) and quality (`imageQuality`) parameters to some methods of this
+plugin, which in other platforms control how selected images are resized or
+re-encoded.
+
+On the web:
+
+* `maxWidth`, `maxHeight` and `imageQuality` are not supported for `gif` images.
+* `imageQuality` only affects `jpg` and `webp` images.
+
+### `getVideo()`
 
-### pickVideo()
 The argument `maxDuration` is not supported on the web.
 
 ## Usage
@@ -65,8 +69,8 @@ should add it to your `pubspec.yaml` as usual.
 
 You should be able to use `package:image_picker` _almost_ as normal.
 
-Once the user has picked a file, the returned `PickedFile` instance will contain a
-`network`-accessible URL (pointing to a location within the browser).
+Once the user has picked a file, the returned `XFile` instance will contain a
+`network`-accessible `Blob` URL (pointing to a location within the browser).
 
 The instance will also let you retrieve the bytes of the selected file across all platforms.
 

packages/image_picker/image_picker_for_web/example/integration_test/image_picker_for_web_test.dart

@@ -33,7 +33,9 @@ void main() {
     plugin = ImagePickerPlugin();
   });
 
-  testWidgets('Can select a file (Deprecated)', (WidgetTester tester) async {
+  testWidgets('getImageFromSource can select a file', (
+    WidgetTester _,
+  ) async {
     final html.FileUploadInputElement mockInput = html.FileUploadInputElement();
 
     final ImagePickerPluginTestOverrides overrides =
@@ -44,29 +46,9 @@ void main() {
     final ImagePickerPlugin plugin = ImagePickerPlugin(overrides: overrides);
 
     // Init the pick file dialog...
-    final Future<PickedFile> file = plugin.pickFile();
-
-    // Mock the browser behavior of selecting a file...
-    mockInput.dispatchEvent(html.Event('change'));
-
-    // Now the file should be available
-    expect(file, completes);
-    // And readable
-    expect((await file).readAsBytes(), completion(isNotEmpty));
-  });
-
-  testWidgets('Can select a file', (WidgetTester tester) async {
-    final html.FileUploadInputElement mockInput = html.FileUploadInputElement();
-
-    final ImagePickerPluginTestOverrides overrides =
-        ImagePickerPluginTestOverrides()
-          ..createInputElement = ((_, __) => mockInput)
-          ..getMultipleFilesFromInput = ((_) => <html.File>[textFile]);
-
-    final ImagePickerPlugin plugin = ImagePickerPlugin(overrides: overrides);
-
-    // Init the pick file dialog...
-    final Future<XFile> image = plugin.getImage(source: ImageSource.camera);
+    final Future<XFile?> image = plugin.getImageFromSource(
+      source: ImageSource.camera,
+    );
 
     // Mock the browser behavior of selecting a file...
     mockInput.dispatchEvent(html.Event('change'));
@@ -75,8 +57,9 @@ void main() {
     expect(image, completes);
 
     // And readable
-    final XFile file = await image;
-    expect(file.readAsBytes(), completion(isNotEmpty));
+    final XFile? file = await image;
+    expect(file, isNotNull);
+    expect(file!.readAsBytes(), completion(isNotEmpty));
     expect(file.name, textFile.name);
     expect(file.length(), completion(textFile.size));
     expect(file.mimeType, textFile.type);
@@ -87,8 +70,9 @@ void main() {
         ));
   });
 
-  testWidgets('getMultiImage can select multiple files',
-      (WidgetTester tester) async {
+  testWidgets('getMultiImageWithOptions can select multiple files', (
+    WidgetTester _,
+  ) async {
     final html.FileUploadInputElement mockInput = html.FileUploadInputElement();
 
     final ImagePickerPluginTestOverrides overrides =
@@ -100,7 +84,7 @@ void main() {
     final ImagePickerPlugin plugin = ImagePickerPlugin(overrides: overrides);
 
     // Init the pick file dialog...
-    final Future<List<XFile>> files = plugin.getMultiImage();
+    final Future<List<XFile>> files = plugin.getMultiImageWithOptions();
 
     // Mock the browser behavior of selecting a file...
     mockInput.dispatchEvent(html.Event('change'));
@@ -118,8 +102,7 @@ void main() {
     expect(secondFile.length(), completion(secondTextFile.size));
   });
 
-  testWidgets('getMedia can select multiple files',
-      (WidgetTester tester) async {
+  testWidgets('getMedia can select multiple files', (WidgetTester _) async {
     final html.FileUploadInputElement mockInput = html.FileUploadInputElement();
 
     final ImagePickerPluginTestOverrides overrides =
@@ -150,7 +133,72 @@ void main() {
     expect(secondFile.length(), completion(secondTextFile.size));
   });
 
-  // There's no good way of detecting when the user has "aborted" the selection.
+  group('cancel event', () {
+    late html.FileUploadInputElement mockInput;
+    late ImagePickerPluginTestOverrides overrides;
+    late ImagePickerPlugin plugin;
+
+    setUp(() {
+      mockInput = html.FileUploadInputElement();
+      overrides = ImagePickerPluginTestOverrides()
+        ..createInputElement = ((_, __) => mockInput)
+        ..getMultipleFilesFromInput = ((_) => <html.File>[textFile]);
+      plugin = ImagePickerPlugin(overrides: overrides);
+    });
+
+    void mockCancel() {
+      mockInput.dispatchEvent(html.Event('cancel'));
+    }
+
+    testWidgets('getFiles - returns empty list', (WidgetTester _) async {
+      final Future<List<XFile>> files = plugin.getFiles();
+      mockCancel();
+
+      expect(files, completes);
+      expect(await files, isEmpty);
+    });
+
+    testWidgets('getMedia - returns empty list', (WidgetTester _) async {
+      final Future<List<XFile>?> files = plugin.getMedia(
+          options: const MediaOptions(
+        allowMultiple: true,
+      ));
+      mockCancel();
+
+      expect(files, completes);
+      expect(await files, isEmpty);
+    });
+
+    testWidgets('getMultiImageWithOptions - returns empty list', (
+      WidgetTester _,
+    ) async {
+      final Future<List<XFile>?> files = plugin.getMultiImageWithOptions();
+      mockCancel();
+
+      expect(files, completes);
+      expect(await files, isEmpty);
+    });
+
+    testWidgets('getImageFromSource - returns null', (WidgetTester _) async {
+      final Future<XFile?> file = plugin.getImageFromSource(
+        source: ImageSource.gallery,
+      );
+      mockCancel();
+
+      expect(file, completes);
+      expect(await file, isNull);
+    });
+
+    testWidgets('getVideo - returns null', (WidgetTester _) async {
+      final Future<XFile?> file = plugin.getVideo(
+        source: ImageSource.gallery,
+      );
+      mockCancel();
+
+      expect(file, completes);
+      expect(await file, isNull);
+    });
+  });
 
   testWidgets('computeCaptureAttribute', (WidgetTester tester) async {
     expect(
@@ -208,4 +256,102 @@ void main() {
       expect(input.attributes, contains('multiple'));
     });
   });
+
+  group('Deprecated methods', () {
+    late html.FileUploadInputElement mockInput;
+    late ImagePickerPluginTestOverrides overrides;
+    late ImagePickerPlugin plugin;
+
+    setUp(() {
+      mockInput = html.FileUploadInputElement();
+      overrides = ImagePickerPluginTestOverrides()
+        ..createInputElement = ((_, __) => mockInput)
+        ..getMultipleFilesFromInput = ((_) => <html.File>[textFile]);
+      plugin = ImagePickerPlugin(overrides: overrides);
+    });
+
+    void mockCancel() {
+      mockInput.dispatchEvent(html.Event('cancel'));
+    }
+
+    void mockChange() {
+      mockInput.dispatchEvent(html.Event('change'));
+    }
+
+    group('getImage', () {
+      testWidgets('can select a file', (WidgetTester _) async {
+        // ignore: deprecated_member_use
+        final Future<XFile?> image = plugin.getImage(
+          source: ImageSource.camera,
+        );
+
+        // Mock the browser behavior when selecting a file...
+        mockChange();
+
+        // Now the file should be available
+        expect(image, completes);
+
+        // And readable
+        final XFile? file = await image;
+        expect(file, isNotNull);
+        expect(file!.readAsBytes(), completion(isNotEmpty));
+        expect(file.name, textFile.name);
+        expect(file.length(), completion(textFile.size));
+        expect(file.mimeType, textFile.type);
+        expect(
+            file.lastModified(),
+            completion(
+              DateTime.fromMillisecondsSinceEpoch(textFile.lastModified!),
+            ));
+      });
+
+      testWidgets('returns null when canceled', (WidgetTester _) async {
+        // ignore: deprecated_member_use
+        final Future<XFile?> file = plugin.getImage(
+          source: ImageSource.gallery,
+        );
+        mockCancel();
+
+        expect(file, completes);
+        expect(await file, isNull);
+      });
+    });
+
+    group('getMultiImage', () {
+      testWidgets('can select multiple files', (WidgetTester _) async {
+        // Override the returned files...
+        overrides.getMultipleFilesFromInput =
+            (_) => <html.File>[textFile, secondTextFile];
+
+        // ignore: deprecated_member_use
+        final Future<List<XFile>> files = plugin.getMultiImage();
+
+        // Mock the browser behavior of selecting a file...
+        mockChange();
+
+        // Now the file should be available
+        expect(files, completes);
+
+        // And readable
+        expect((await files).first.readAsBytes(), completion(isNotEmpty));
+
+        // Peek into the second file...
+        final XFile secondFile = (await files).elementAt(1);
+        expect(secondFile.readAsBytes(), completion(isNotEmpty));
+        expect(secondFile.name, secondTextFile.name);
+        expect(secondFile.length(), completion(secondTextFile.size));
+      });
+
+      testWidgets('returns an empty list when canceled', (
+        WidgetTester _,
+      ) async {
+        // ignore: deprecated_member_use
+        final Future<List<XFile>?> files = plugin.getMultiImage();
+        mockCancel();
+
+        expect(files, completes);
+        expect(await files, isEmpty);
+      });
+    });
+  });
 }