Revert "[macos] Revert check on FlutterCodecs and refactor message fu…

shell/platform/darwin/common/framework/Source/FlutterChannels.mm

@@ -51,7 +51,7 @@ - (void)sendMessage:(id)message {
 - (void)sendMessage:(id)message reply:(FlutterReply)callback {
   FlutterBinaryReply reply = ^(NSData* data) {
     if (callback)
-      callback(data.length > 0 ? [_codec decode:data] : nil);
+      callback([_codec decode:data]);
   };
   [_messenger sendOnChannel:_name message:[_codec encode:message] binaryReply:reply];
 }

shell/platform/darwin/common/framework/Source/FlutterCodecs.mm

@@ -73,7 +73,7 @@ - (NSData*)encode:(id)message {
 }
 
 - (id)decode:(NSData*)message {
-  if (message == nil)
+  if (message.length == 0)
     return nil;
   BOOL isSimpleValue = NO;
   id decoded = nil;

shell/platform/darwin/macos/framework/Source/FLEEngine.mm

@@ -332,35 +332,42 @@ - (void)shutDownEngine {
 #pragma mark - FlutterBinaryMessenger
 
 - (void)sendOnChannel:(nonnull NSString*)channel message:(nullable NSData*)message {
-  [self sendOnChannel:channel message:message binaryReply:nil];
+  FlutterPlatformMessage platformMessage = {
+      .struct_size = sizeof(FlutterPlatformMessage),
+      .channel = [channel UTF8String],
+      .message = static_cast<const uint8_t*>(message.bytes),
+      .message_size = message.length,
+  };
+
+  FlutterEngineResult result = FlutterEngineSendPlatformMessage(_engine, &platformMessage);
+  if (result != kSuccess) {
+    NSLog(@"Failed to send message to Flutter engine on channel '%@' (%d).", channel, result);
+  }
 }
 
 - (void)sendOnChannel:(NSString*)channel
               message:(NSData* _Nullable)message
           binaryReply:(FlutterBinaryReply _Nullable)callback {
-  FlutterPlatformMessageResponseHandle* response_handle = nullptr;
-
-  if (callback) {
-    struct Captures {
-      FlutterBinaryReply reply;
-    };
-    auto captures = std::make_unique<Captures>();
-    captures->reply = callback;
-    auto message_reply = [](const uint8_t* data, size_t data_size, void* user_data) {
-      auto captures = reinterpret_cast<Captures*>(user_data);
-      NSData* reply_data = [NSData dataWithBytes:static_cast<const void*>(data) length:data_size];
-      captures->reply(reply_data);
-      delete captures;
-    };
+  struct Captures {
+    FlutterBinaryReply reply;
+  };
+  auto captures = std::make_unique<Captures>();
+  captures->reply = callback;
+  auto message_reply = [](const uint8_t* data, size_t data_size, void* user_data) {
+    auto captures = reinterpret_cast<Captures*>(user_data);
+    NSData* reply_data = [NSData dataWithBytes:(void*)data length:data_size];
+    captures->reply(reply_data);
+    delete captures;
+  };
 
-    FlutterEngineResult create_result = FlutterPlatformMessageCreateResponseHandle(
-        _engine, message_reply, captures.get(), &response_handle);
-    if (create_result != kSuccess) {
-      NSLog(@"Failed to create a FlutterPlatformMessageResponseHandle (%d)", create_result);
-      return;
-    }
-    captures.release();
+  FlutterPlatformMessageResponseHandle* response_handle = nullptr;
+  FlutterEngineResult result = FlutterPlatformMessageCreateResponseHandle(
+      _engine, message_reply, captures.get(), &response_handle);
+  if (result != kSuccess) {
+    NSLog(@"Failed to create a FlutterPlatformMessageResponseHandle");
+    return;
   }
+  captures.release();
 
   FlutterPlatformMessage platformMessage = {
       .struct_size = sizeof(FlutterPlatformMessage),
@@ -370,19 +377,15 @@ - (void)sendOnChannel:(NSString*)channel
       .response_handle = response_handle,
   };
 
-  FlutterEngineResult message_result = FlutterEngineSendPlatformMessage(_engine, &platformMessage);
-  if (message_result != kSuccess) {
-    NSLog(@"Failed to send message to Flutter engine on channel '%@' (%d).", channel,
-          message_result);
+  result = FlutterEngineSendPlatformMessage(_engine, &platformMessage);
+  if (result != kSuccess) {
+    NSLog(@"Failed to send message to Flutter engine on channel '%@' (%d).", channel, result);
   }
 
-  if (response_handle != nullptr) {
-    FlutterEngineResult release_result =
-        FlutterPlatformMessageReleaseResponseHandle(_engine, response_handle);
-    if (release_result != kSuccess) {
-      NSLog(@"Failed to release the response handle (%d).", release_result);
-    };
-  }
+  result = FlutterPlatformMessageReleaseResponseHandle(_engine, response_handle);
+  if (result != kSuccess) {
+    NSLog(@"Failed to release the response handle");
+  };
 }
 
 - (void)setMessageHandlerOnChannel:(nonnull NSString*)channel