SendPlatformMessage allow null message value (flutter/engine#9781)

engine/src/flutter/shell/platform/embedder/embedder.cc

@@ -814,8 +814,14 @@ FlutterEngineResult FlutterEngineSendPlatformMessage(
     return LOG_EMBEDDER_ERROR(kInvalidArguments);
   }
 
-  if (SAFE_ACCESS(flutter_message, channel, nullptr) == nullptr ||
-      SAFE_ACCESS(flutter_message, message, nullptr) == nullptr) {
+  if (SAFE_ACCESS(flutter_message, channel, nullptr) == nullptr) {
+    return LOG_EMBEDDER_ERROR(kInvalidArguments);
+  }
+
+  size_t message_size = SAFE_ACCESS(flutter_message, message_size, 0);
+  const uint8_t* message_data = SAFE_ACCESS(flutter_message, message, nullptr);
+
+  if (message_size != 0 && message_data == nullptr) {
     return LOG_EMBEDDER_ERROR(kInvalidArguments);
   }
 
@@ -827,12 +833,16 @@ FlutterEngineResult FlutterEngineSendPlatformMessage(
     response = response_handle->message->response();
   }
 
-  auto message = fml::MakeRefCounted<flutter::PlatformMessage>(
-      flutter_message->channel,
-      std::vector<uint8_t>(
-          flutter_message->message,
-          flutter_message->message + flutter_message->message_size),
-      response);
+  fml::RefPtr<flutter::PlatformMessage> message;
+  if (message_size == 0) {
+    message = fml::MakeRefCounted<flutter::PlatformMessage>(
+        flutter_message->channel, response);
+  } else {
+    message = fml::MakeRefCounted<flutter::PlatformMessage>(
+        flutter_message->channel,
+        std::vector<uint8_t>(message_data, message_data + message_size),
+        response);
+  }
 
   return reinterpret_cast<flutter::EmbedderEngine*>(engine)
                  ->SendPlatformMessage(std::move(message))

engine/src/flutter/shell/platform/embedder/fixtures/main.dart

@@ -167,3 +167,14 @@ void platform_messages_no_response() {
   };
   signalNativeTest();
 }
+
+@pragma('vm:entry-point')
+void null_platform_messages() {
+  window.onPlatformMessage =
+      (String name, ByteData data, PlatformMessageResponseCallback callback) {
+    // This checks if the platform_message null data is converted to Flutter null.
+    signalNativeMessage((null == data).toString());
+    callback(data);
+  };
+  signalNativeTest();
+}

engine/src/flutter/shell/platform/embedder/tests/embedder_unittests.cc

@@ -400,5 +400,70 @@ TEST_F(EmbedderTest, PlatformMessagesCanBeSentWithoutResponseHandles) {
   message.Wait();
 }
 
+//------------------------------------------------------------------------------
+/// Tests that a null platform message can be sent.
+///
+TEST_F(EmbedderTest, NullPlatformMessagesCanBeSent) {
+  auto& context = GetEmbedderContext();
+  EmbedderConfigBuilder builder(context);
+
+  builder.SetDartEntrypoint("null_platform_messages");
+
+  fml::AutoResetWaitableEvent ready, message;
+  context.AddNativeCallback(
+      "SignalNativeTest",
+      CREATE_NATIVE_ENTRY(
+          [&ready](Dart_NativeArguments args) { ready.Signal(); }));
+  context.AddNativeCallback(
+      "SignalNativeMessage",
+      CREATE_NATIVE_ENTRY(([&message](Dart_NativeArguments args) {
+        auto received_message = tonic::DartConverter<std::string>::FromDart(
+            Dart_GetNativeArgument(args, 0));
+        ASSERT_EQ("true", received_message);
+        message.Signal();
+      })));
+
+  auto engine = builder.LaunchEngine();
+
+  ASSERT_TRUE(engine.is_valid());
+  ready.Wait();
+
+  FlutterPlatformMessage platform_message = {};
+  platform_message.struct_size = sizeof(FlutterPlatformMessage);
+  platform_message.channel = "test_channel";
+  platform_message.message = nullptr;
+  platform_message.message_size = 0;
+  platform_message.response_handle = nullptr;  // No response needed.
+
+  auto result =
+      FlutterEngineSendPlatformMessage(engine.get(), &platform_message);
+  ASSERT_EQ(result, kSuccess);
+  message.Wait();
+}
+
+//------------------------------------------------------------------------------
+/// Tests that a null platform message cannot be send if the message_size
+/// isn't equals to 0.
+///
+TEST_F(EmbedderTest, InvalidPlatformMessages) {
+  auto& context = GetEmbedderContext();
+  EmbedderConfigBuilder builder(context);
+
+  auto engine = builder.LaunchEngine();
+
+  ASSERT_TRUE(engine.is_valid());
+
+  FlutterPlatformMessage platform_message = {};
+  platform_message.struct_size = sizeof(FlutterPlatformMessage);
+  platform_message.channel = "test_channel";
+  platform_message.message = nullptr;
+  platform_message.message_size = 1;
+  platform_message.response_handle = nullptr;  // No response needed.
+
+  auto result =
+      FlutterEngineSendPlatformMessage(engine.get(), &platform_message);
+  ASSERT_EQ(result, kInvalidArguments);
+}
+
 }  // namespace testing
 }  // namespace flutter