Revert "Started handling messages from background isolates." (#111318)

dev/integration_tests/channels/android/app/src/main/AndroidManifest.xml

@@ -18,7 +18,6 @@ found in the LICENSE file. -->
          Application and put your custom class here. -->
     <application android:name="${applicationName}" android:label="channels" android:icon="@mipmap/ic_launcher">
         <activity android:name=".MainActivity"
-                  android:exported="true"
                   android:launchMode="singleTop"
                   android:theme="@android:style/Theme.Black.NoTitleBar"
                   android:configChanges="orientation|keyboardHidden|keyboard|screenSize|locale|layoutDirection|fontScale|screenLayout|density|uiMode"

dev/integration_tests/channels/ios/Runner/AppDelegate.m

@@ -114,18 +114,7 @@ const UInt8 PAIR = 129;
     [FlutterMethodChannel methodChannelWithName:@"std-method"
                                 binaryMessenger:flutterController
                                           codec:[FlutterStandardMethodCodec codecWithReaderWriter:extendedReaderWriter]]];
-
+  return [super application:application didFinishLaunchingWithOptions:launchOptions];
-  [[FlutterBasicMessageChannel
-      messageChannelWithName:@"std-echo"
-             binaryMessenger:flutterController
-                       codec:[FlutterStandardMessageCodec
-                                 codecWithReaderWriter:extendedReaderWriter]]
-      setMessageHandler:^(id message, FlutterReply reply) {
-        reply(message);
-      }];
-
-  return [super application:application
-      didFinishLaunchingWithOptions:launchOptions];
 }
 
 - (void)setupMessagingHandshakeOnChannel:(FlutterBasicMessageChannel*)channel {

dev/integration_tests/channels/lib/main.dart

@@ -173,8 +173,6 @@ class _TestAppState extends State<TestApp> {
     () => basicStringMessageToUnknownChannel(),
     () => basicJsonMessageToUnknownChannel(),
     () => basicStandardMessageToUnknownChannel(),
-    if (Platform.isIOS)
-      () => basicBackgroundStandardEcho(123),
   ];
   Future<TestStepResult>? _result;
   int _step = 0;

dev/integration_tests/channels/lib/src/basic_messaging.dart

@@ -3,7 +3,6 @@
 // found in the LICENSE file.
 
 import 'dart:async';
-import 'dart:isolate';
 
 import 'package:flutter/services.dart';
 
@@ -79,41 +78,6 @@ Future<TestStepResult> basicStandardHandshake(dynamic message) async {
       'Standard >${toString(message)}<', channel, message);
 }
 
-Future<void> _basicBackgroundStandardEchoMain(List<Object> args) async {
-  final SendPort sendPort = args[2] as SendPort;
-  final Object message = args[1];
-  final String name = 'Background Echo >${toString(message)}<';
-  const String description =
-      'Uses a platform channel from a background isolate.';
-  try {
-    BackgroundIsolateBinaryMessenger.ensureInitialized(
-        args[0] as RootIsolateToken);
-    const BasicMessageChannel<dynamic> channel = BasicMessageChannel<dynamic>(
-      'std-echo',
-      ExtendedStandardMessageCodec(),
-    );
-    final Object response = await channel.send(message) as Object;
-
-    final TestStatus testStatus = TestStepResult.deepEquals(message, response)
-        ? TestStatus.ok
-        : TestStatus.failed;
-    sendPort.send(TestStepResult(name, description, testStatus));
-  } catch (ex) {
-    sendPort.send(TestStepResult(name, description, TestStatus.failed,
-        error: ex.toString()));
-  }
-}
-
-Future<TestStepResult> basicBackgroundStandardEcho(Object message) async {
-  final ReceivePort receivePort = ReceivePort();
-  Isolate.spawn(_basicBackgroundStandardEchoMain, <Object>[
-    ServicesBinding.instance.rootIsolateToken!,
-    message,
-    receivePort.sendPort,
-  ]);
-  return await receivePort.first as TestStepResult;
-}
-
 Future<TestStepResult> basicBinaryMessageToUnknownChannel() async {
   const BasicMessageChannel<ByteData?> channel =
       BasicMessageChannel<ByteData?>(

dev/integration_tests/channels/lib/src/test_step.dart

@@ -90,8 +90,6 @@ class TestStepResult {
       ],
     );
   }
-
-  static bool deepEquals(dynamic a, dynamic b) => _deepEquals(a, b);
 }
 
 Future<TestStepResult> resultOfHandshake(

packages/flutter/lib/src/services/binding.dart

@@ -82,21 +82,6 @@ mixin ServicesBinding on BindingBase, SchedulerBinding {
   BinaryMessenger get defaultBinaryMessenger => _defaultBinaryMessenger;
   late final BinaryMessenger _defaultBinaryMessenger;
 
-  /// A token that represents the root isolate, used for coordinating with background
-  /// isolates.
-  ///
-  /// This property is primarily intended for use with
-  /// [BackgroundIsolateBinaryMessenger.ensureInitialized], which takes a
-  /// [RootIsolateToken] as its argument. The value `null` is returned when
-  /// executed from background isolates.
-  ui.RootIsolateToken? get rootIsolateToken => ui.RootIsolateToken.instance;
-
-  /// Returns `true` if executed on a background (non-root) isolate.
-  ///
-  /// The value `false` will always be returned on web since there is no notion
-  /// of root/background isolates on the web.
-  bool get useBackgroundIsolateBinaryMessenger => !kIsWeb && rootIsolateToken == null;
-
   /// The low level buffering and dispatch mechanism for messages sent by
   /// plugins on the engine side to their corresponding plugin code on
   /// the framework side.

packages/flutter/lib/src/services/platform_channel.dart

@@ -4,8 +4,6 @@
 
 import 'dart:async';
 import 'dart:developer';
-import 'dart:isolate' show ReceivePort;
-import 'dart:ui' as ui;
 
 import 'package:flutter/foundation.dart';
 
@@ -15,7 +13,6 @@ import 'debug.dart' show debugProfilePlatformChannels;
 import 'message_codec.dart';
 import 'message_codecs.dart';
 
-export 'dart:ui' show RootIsolateToken;
 export 'binary_messenger.dart' show BinaryMessenger;
 export 'message_codec.dart' show MessageCodec, MethodCall, MethodCodec;
 
@@ -126,93 +123,6 @@ void _debugRecordDownStream(String channelTypeName, String name,
   _debugLaunchProfilePlatformChannels();
 }
 
-/// A [BinaryMessenger] for use on background (non-root) isolates.
-class BackgroundIsolateBinaryMessenger extends BinaryMessenger {
-  BackgroundIsolateBinaryMessenger._();
-
-  final ReceivePort _receivePort = ReceivePort();
-  final Map<int, Completer<ByteData?>> _completers = <int, Completer<ByteData?>>{};
-  int _messageCount = 0;
-
-  /// The existing instance of this class, if any.
-  ///
-  /// Throws if [ensureInitialized] has not been called at least once.
-  static BinaryMessenger get instance {
-    if (_instance == null) {
-      throw StateError(
-          'The BackgroundIsolateBinaryMessenger.instance value is invalid '
-          'until BackgroundIsolateBinaryMessenger.ensureInitialized is '
-          'executed.');
-    }
-    return _instance!;
-  }
-
-  static BinaryMessenger? _instance;
-
-  /// Ensures that [BackgroundIsolateBinaryMessenger.instance] has been initialized.
-  ///
-  /// The argument should be the value obtained from [ServicesBinding.rootIsolateToken]
-  /// on the root isolate.
-  ///
-  /// This function is idempotent (calling it multiple times is harmless but has no effect).
-  static void ensureInitialized(ui.RootIsolateToken token) {
-    if (_instance == null) {
-      ui.PlatformDispatcher.instance.registerBackgroundIsolate(token);
-      final BackgroundIsolateBinaryMessenger portBinaryMessenger = BackgroundIsolateBinaryMessenger._();
-      _instance = portBinaryMessenger;
-      portBinaryMessenger._receivePort.listen((dynamic message) {
-        try {
-          final List<dynamic> args = message as List<dynamic>;
-          final int identifier = args[0] as int;
-          final Uint8List bytes = args[1] as Uint8List;
-          final ByteData byteData = ByteData.sublistView(bytes);
-          portBinaryMessenger._completers.remove(identifier)!.complete(byteData);
-        } catch (exception, stack) {
-          FlutterError.reportError(FlutterErrorDetails(
-            exception: exception,
-            stack: stack,
-            library: 'services library',
-            context:
-                ErrorDescription('during a platform message response callback'),
-          ));
-        }
-      });
-    }
-  }
-
-  @override
-  Future<void> handlePlatformMessage(String channel, ByteData? data, ui.PlatformMessageResponseCallback? callback) {
-    throw UnimplementedError('handlePlatformMessage is deprecated.');
-  }
-
-  @override
-  Future<ByteData?>? send(String channel, ByteData? message) {
-    final Completer<ByteData?> completer = Completer<ByteData?>();
-    _messageCount += 1;
-    final int messageIdentifier = _messageCount;
-    _completers[messageIdentifier] = completer;
-    ui.PlatformDispatcher.instance.sendPortPlatformMessage(
-      channel,
-      message,
-      messageIdentifier,
-      _receivePort.sendPort,
-    );
-    return completer.future;
-  }
-
-  @override
-  void setMessageHandler(String channel, MessageHandler? handler) {
-    throw UnsupportedError(
-        'Background isolates do not support setMessageHandler(). Messages from the host platform always go to the root isolate.');
-  }
-}
-
-BinaryMessenger _findBinaryMessenger() {
-  return ServicesBinding.instance.useBackgroundIsolateBinaryMessenger
-      ? BackgroundIsolateBinaryMessenger.instance
-      : ServicesBinding.instance.defaultBinaryMessenger;
-}
-
 /// A named channel for communicating with platform plugins using asynchronous
 /// message passing.
 ///
@@ -250,14 +160,10 @@ class BasicMessageChannel<T> {
   /// The message codec used by this channel, not null.
   final MessageCodec<T> codec;
 
-  /// The messenger which sends the bytes for this channel.
+  /// The messenger which sends the bytes for this channel, not null.
-  ///
-  /// On the root isolate or web, this defaults to the
-  /// [ServicesBinding.defaultBinaryMessenger]. In other contexts the default
-  /// value is a [BackgroundIsolateBinaryMessenger] from
-  /// [BackgroundIsolateBinaryMessenger.ensureInitialized].
   BinaryMessenger get binaryMessenger {
-    final BinaryMessenger result = _binaryMessenger ?? _findBinaryMessenger();
+    final BinaryMessenger result =
+        _binaryMessenger ?? ServicesBinding.instance.defaultBinaryMessenger;
     return !kReleaseMode && debugProfilePlatformChannels
         ? _debugBinaryMessengers[this] ??= _ProfiledBinaryMessenger(
             // ignore: no_runtimetype_tostring
@@ -340,14 +246,12 @@ class MethodChannel {
   /// The message codec used by this channel, not null.
   final MethodCodec codec;
 
-  /// The messenger which sends the bytes for this channel.
+  /// The messenger used by this channel to send platform messages.
   ///
-  /// On the root isolate or web, this defaults to the
+  /// The messenger may not be null.
-  /// [ServicesBinding.defaultBinaryMessenger]. In other contexts the default
-  /// value is a [BackgroundIsolateBinaryMessenger] from
-  /// [BackgroundIsolateBinaryMessenger.ensureInitialized].
   BinaryMessenger get binaryMessenger {
-    final BinaryMessenger result = _binaryMessenger ?? _findBinaryMessenger();
+    final BinaryMessenger result =
+        _binaryMessenger ?? ServicesBinding.instance.defaultBinaryMessenger;
     return !kReleaseMode && debugProfilePlatformChannels
         ? _debugBinaryMessengers[this] ??= _ProfiledBinaryMessenger(
             // ignore: no_runtimetype_tostring
@@ -696,14 +600,8 @@ class EventChannel {
   /// The message codec used by this channel, not null.
   final MethodCodec codec;
 
-  /// The messenger which sends the bytes for this channel.
+  /// The messenger used by this channel to send platform messages, not null.
-  ///
+  BinaryMessenger get binaryMessenger => _binaryMessenger ?? ServicesBinding.instance.defaultBinaryMessenger;
-  /// On the root isolate or web, this defaults to the
-  /// [ServicesBinding.defaultBinaryMessenger]. In other contexts the default
-  /// value is a [BackgroundIsolateBinaryMessenger] from
-  /// [BackgroundIsolateBinaryMessenger.ensureInitialized].
-  BinaryMessenger get binaryMessenger =>
-      _binaryMessenger ?? _findBinaryMessenger();
   final BinaryMessenger? _binaryMessenger;
 
   /// Sets up a broadcast stream for receiving events on this channel.

packages/flutter_test/lib/src/binding.dart

@@ -104,9 +104,6 @@ mixin TestDefaultBinaryMessengerBinding on BindingBase, ServicesBinding {
   TestDefaultBinaryMessenger createBinaryMessenger() {
     return TestDefaultBinaryMessenger(super.createBinaryMessenger());
   }
-
-  @override
-  bool get useBackgroundIsolateBinaryMessenger => false;
 }
 
 /// Base class for bindings used by widgets library tests.