Ignore some missing plugins. (#8852)

Fixes #8850

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

@@ -42,7 +42,7 @@ class MethodCall {
   ///
   /// Must be a valid value for the [MethodCodec] used.
   final dynamic arguments;
-  
+
   @override
   bool operator== (dynamic other) {
     if (identical(this, other))
@@ -64,7 +64,7 @@ class MethodCall {
       return b is Map && _deepEqualsMap(a, b);
     return false;
   }
-  
+
   bool _deepEqualsList(List<dynamic> a, List<dynamic> b) {
     if (a.length != b.length)
       return false;
@@ -84,7 +84,7 @@ class MethodCall {
     }
     return true;
   }
-  
+
   @override
   String toString() => '$runtimeType($method, $arguments)';
 }
@@ -120,7 +120,7 @@ abstract class MethodCodec {
 
   /// Encodes a successful [result] into a binary envelope.
   ByteData encodeSuccessEnvelope(dynamic result);
-  
+
   /// Encodes an error result into a binary envelope.
   ///
   /// The specified error [code], human-readable error [message], and error
@@ -166,3 +166,9 @@ class PlatformException implements Exception {
   @override
   String toString() => 'PlatformException($code, $message, $details)';
 }
+
+/// Thrown to indicate that a platform interaction failed to find the plugin.
+class MissingPluginException implements Exception {
+  @override
+  String toString() => 'MissingPluginException';
+}

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

@@ -121,6 +121,8 @@ class JSONMethodCodec implements MethodCodec {
 
   @override
   dynamic decodeEnvelope(ByteData envelope) {
+    if (envelope == null)
+      throw new MissingPluginException();
     final dynamic decoded = const JSONMessageCodec().decodeMessage(envelope);
     if (decoded is! List)
       throw new FormatException('Expected envelope List, got $decoded');
@@ -460,8 +462,10 @@ class StandardMethodCodec implements MethodCodec {
 
   @override
   dynamic decodeEnvelope(ByteData envelope) {
+    if (envelope == null)
+      throw new MissingPluginException();
     // First byte is zero in success case, and non-zero otherwise.
-    if (envelope == null || envelope.lengthInBytes == 0)
+    if (envelope.lengthInBytes == 0)
       throw const FormatException('Expected envelope, got nothing');
     final ReadBuffer buffer = new ReadBuffer(envelope);
     if (buffer.getUint8() == 0)

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

@@ -261,3 +261,22 @@ class PlatformMethodChannel {
     return controller.stream;
   }
 }
+
+/// A [PlatformMethodChannel] that ignores missing platform plugins.
+///
+/// When [invokeMethod] fails to find the platform plugin, it returns null
+/// instead of throwing an exception.
+class OptionalPlatformMethodChannel extends PlatformMethodChannel {
+  /// Creates a [PlatformMethodChannel] that ignores missing platform plugins.
+  const OptionalPlatformMethodChannel(String name, [MethodCodec codec = const StandardMethodCodec()])
+    : super(name, codec);
+
+  @override
+  Future<dynamic> invokeMethod(String method, [dynamic arguments]) async {
+    try {
+      return await super.invokeMethod(method, arguments);
+    } on MissingPluginException {
+      return null;
+    }
+  }
+}

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

@@ -16,13 +16,17 @@ class SystemChannels {
   );
 
   /// A JSON [PlatformMethodChannel] for invoking miscellaneous platform methods.
-  static const PlatformMethodChannel platform = const PlatformMethodChannel(
+  ///
+  /// Ignores missing plugins.
+  static const PlatformMethodChannel platform = const OptionalPlatformMethodChannel(
       'flutter/platform',
       const JSONMethodCodec(),
   );
 
   /// A JSON [PlatformMethodChannel] for handling text input.
-  static const PlatformMethodChannel textInput = const PlatformMethodChannel(
+  ///
+  /// Ignores missing plugins.
+  static const PlatformMethodChannel textInput = const OptionalPlatformMethodChannel(
       'flutter/textinput',
       const JSONMethodCodec(),
   );

packages/flutter/test/services/system_chrome_test.dart

@@ -2,6 +2,8 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+import 'dart:typed_data';
+
 import 'package:flutter/services.dart';
 import 'package:flutter_test/flutter_test.dart';
 
@@ -54,6 +56,21 @@ void main() {
     )]));
   });
 
+  test('setApplicationSwitcherDescription missing plugin', () async {
+    final List<ByteData> log = <ByteData>[];
+
+    PlatformMessages.setMockBinaryMessageHandler('flutter/platform', (ByteData message) {
+      log.add(message);
+      return null;
+    });
+
+    await SystemChrome.setApplicationSwitcherDescription(
+      const ApplicationSwitcherDescription(label: 'Example label', primaryColor: 0xFF00FF00)
+    );
+
+    expect(log, isNotEmpty);
+  });
+
   test('setEnabledSystemUIOverlays control test', () async {
     final List<MethodCall> log = <MethodCall>[];