[web] Calling platform message callback after copy (flutter/engine#15950)

* Calling platform message callback after copy

* addressing pr comments

* adding unit tests to clipbpard.dart

engine/src/flutter/lib/web_ui/lib/src/engine/clipboard.dart

@@ -7,26 +7,51 @@ part of engine;
 /// Handles clipboard related platform messages.
 class ClipboardMessageHandler {
   /// Helper to handle copy to clipboard functionality.
-  final CopyToClipboardStrategy _copyToClipboardStrategy =
-      CopyToClipboardStrategy();
+  CopyToClipboardStrategy _copyToClipboardStrategy = CopyToClipboardStrategy();
 
   /// Helper to handle copy to clipboard functionality.
-  final PasteFromClipboardStrategy _pasteFromClipboardStrategy =
+  PasteFromClipboardStrategy _pasteFromClipboardStrategy =
       PasteFromClipboardStrategy();
 
   /// Handles the platform message which stores the given text to the clipboard.
-  void setDataMethodCall(MethodCall methodCall) {
-    _copyToClipboardStrategy.setData(methodCall.arguments['text']);
+  void setDataMethodCall(
+      MethodCall methodCall, ui.PlatformMessageResponseCallback callback) {
+    const MethodCodec codec = JSONMethodCodec();
+    _copyToClipboardStrategy
+        .setData(methodCall.arguments['text'])
+        .then((bool success) {
+      if (success) {
+        callback(codec.encodeSuccessEnvelope(true));
+      } else {
+        callback(codec.encodeErrorEnvelope(
+            code: 'copy_fail', message: 'Clipboard.setData failed'));
+      }
+    }).catchError((_) {
+      callback(codec.encodeErrorEnvelope(
+          code: 'copy_fail', message: 'Clipboard.setData failed'));
+    });
   }
 
   /// Handles the platform message which retrieves text data from the clipboard.
   void getDataMethodCall(ui.PlatformMessageResponseCallback callback) {
+    const MethodCodec codec = JSONMethodCodec();
     _pasteFromClipboardStrategy.getData().then((String data) {
-      const MethodCodec codec = JSONMethodCodec();
       final Map<String, dynamic> map = {'text': data};
       callback(codec.encodeSuccessEnvelope(map));
-    }).catchError(
-        (error) => print('Could not get text from clipboard: $error'));
+    }).catchError((error) {
+      print('Could not get text from clipboard: $error');
+      callback(codec.encodeErrorEnvelope(
+          code: 'paste_fail', message: 'Clipboard.getData failed'));
+    });
+  }
+
+  /// Methods used by tests.
+  set pasteFromClipboardStrategy(PasteFromClipboardStrategy strategy) {
+    _pasteFromClipboardStrategy = strategy;
+  }
+
+  set copyToClipboardStrategy(CopyToClipboardStrategy strategy) {
+    _copyToClipboardStrategy = strategy;
   }
 }
 
@@ -42,7 +67,11 @@ abstract class CopyToClipboardStrategy {
   }
 
   /// Places the text onto the browser Clipboard.
-  void setData(String text);
+  ///
+  /// Returns `true` for a successful action.
+  ///
+  /// Returns `false` for an uncessful action or when there is an excaption.
+  Future<bool> setData(String text);
 }
 
 /// Provides functionality for reading text from clipboard.
@@ -67,10 +96,14 @@ abstract class PasteFromClipboardStrategy {
 /// See: https://developer.mozilla.org/en-US/docs/Web/API/Clipboard_API
 class ClipboardAPICopyStrategy implements CopyToClipboardStrategy {
   @override
-  void setData(String text) {
-    html.window.navigator.clipboard
-        .writeText(text)
-        .catchError((error) => print('Could not copy text: $error'));
+  Future<bool> setData(String text) async {
+    try {
+      await html.window.navigator.clipboard.writeText(text);
+    } catch (e) {
+      print('copy is not successful ${e.message}');
+      return Future.value(false);
+    }
+    return Future.value(true);
   }
 }
 
@@ -90,15 +123,20 @@ class ClipboardAPIPasteStrategy implements PasteFromClipboardStrategy {
 /// Provides a fallback strategy for browsers which does not support ClipboardAPI.
 class ExecCommandCopyStrategy implements CopyToClipboardStrategy {
   @override
-  void setData(String text) {
+  Future<bool> setData(String text) {
+    return Future.value(_setDataSync(text));
+  }
+
+  bool _setDataSync(String text) {
     // Copy content to clipboard with execCommand.
     // See: https://developers.google.com/web/updates/2015/04/cut-and-copy-commands
     final html.TextAreaElement tempTextArea = _appendTemporaryTextArea();
     tempTextArea.value = text;
     tempTextArea.focus();
     tempTextArea.select();
+    bool result = false;
     try {
-      final bool result = html.document.execCommand('copy');
+      result = html.document.execCommand('copy');
       if (!result) {
         print('copy is not successful');
       }
@@ -107,6 +145,7 @@ class ExecCommandCopyStrategy implements CopyToClipboardStrategy {
     } finally {
       _removeTemporaryTextArea(tempTextArea);
     }
+    return result;
   }
 
   html.TextAreaElement _appendTemporaryTextArea() {

engine/src/flutter/lib/web_ui/lib/src/engine/window.dart

@@ -170,7 +170,7 @@ class EngineWindow extends ui.Window {
             // There are no default system sounds on web.
             return;
           case 'Clipboard.setData':
-            ClipboardMessageHandler().setDataMethodCall(decoded);
+            ClipboardMessageHandler().setDataMethodCall(decoded, callback);
             return;
           case 'Clipboard.getData':
             ClipboardMessageHandler().getDataMethodCall(callback);

engine/src/flutter/lib/web_ui/test/clipboard_test.dart

@@ -0,0 +1,97 @@
+// Copyright 2013 The Flutter Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+import 'dart:async';
+import 'dart:typed_data';
+
+import 'package:mockito/mockito.dart';
+import 'package:test/test.dart';
+import 'package:ui/ui.dart' as ui;
+import 'package:ui/src/engine.dart';
+
+Future<void> main() async {
+  await ui.webOnlyInitializeTestDomRenderer();
+  group('message handler', () {
+    const String testText = 'test text';
+
+    final Future<bool> success = Future.value(true);
+    final Future<bool> failure = Future.value(false);
+    final Future<String> pasteTest = Future.value(testText);
+
+    ClipboardMessageHandler clipboardMessageHandler;
+    ClipboardAPICopyStrategy clipboardAPICopyStrategy =
+        MockClipboardAPICopyStrategy();
+    ClipboardAPIPasteStrategy clipboardAPIPasteStrategy =
+        MockClipboardAPIPasteStrategy();
+
+    setUp(() {
+      clipboardMessageHandler = new ClipboardMessageHandler();
+      clipboardAPICopyStrategy = MockClipboardAPICopyStrategy();
+      clipboardAPIPasteStrategy = MockClipboardAPIPasteStrategy();
+      clipboardMessageHandler.copyToClipboardStrategy =
+          clipboardAPICopyStrategy;
+      clipboardMessageHandler.pasteFromClipboardStrategy =
+          clipboardAPIPasteStrategy;
+    });
+
+    test('set data successful', () async {
+      when(clipboardAPICopyStrategy.setData(testText))
+          .thenAnswer((_) => success);
+      const MethodCodec codec = JSONMethodCodec();
+      bool result = false;
+      ui.PlatformMessageResponseCallback callback = (ByteData data) {
+        result = codec.decodeEnvelope(data);
+      };
+
+      await clipboardMessageHandler.setDataMethodCall(
+          const MethodCall('Clipboard.setData', <String, dynamic>{
+            'text': testText,
+          }),
+          callback);
+
+      await expectLater(result, true);
+    });
+
+    test('set data error', () async {
+      when(clipboardAPICopyStrategy.setData(testText))
+          .thenAnswer((_) => failure);
+      const MethodCodec codec = JSONMethodCodec();
+      ByteData result;
+      ui.PlatformMessageResponseCallback callback = (ByteData data) {
+        result = data;
+      };
+
+      await clipboardMessageHandler.setDataMethodCall(
+          const MethodCall('Clipboard.setData', <String, dynamic>{
+            'text': testText,
+          }),
+          callback);
+
+      expect(() async {
+        codec.decodeEnvelope(result);
+      }, throwsA(TypeMatcher<PlatformException>()
+          .having((e) => e.code, 'code', equals('copy_fail'))));
+    });
+
+    test('get data successful', () async {
+      when(clipboardAPIPasteStrategy.getData())
+          .thenAnswer((_) => pasteTest);
+      const MethodCodec codec = JSONMethodCodec();
+      Map<String, dynamic> result;
+      ui.PlatformMessageResponseCallback callback = (ByteData data) {
+        result = codec.decodeEnvelope(data);
+      };
+
+      await clipboardMessageHandler.getDataMethodCall(callback);
+
+      await expectLater(result['text'], testText);
+    });
+  });
+}
+
+class MockClipboardAPICopyStrategy extends Mock
+    implements ClipboardAPICopyStrategy {}
+
+class MockClipboardAPIPasteStrategy extends Mock
+    implements ClipboardAPIPasteStrategy {}