eliminated the copies when sending data to and from objc

Author: gaaclarke

shell/platform/darwin/common/buffer_conversions.h

@@ -15,9 +15,9 @@ namespace flutter {
 
 fml::MallocMapping CopyNSDataToMapping(NSData* data);
 
-NSData* CopyMappingToNSData(fml::MallocMapping buffer);
+NSData* ConvertMappingToNSData(fml::MallocMapping buffer);
 
-std::unique_ptr<fml::Mapping> CopyNSDataToMappingPtr(NSData* data);
+std::unique_ptr<fml::Mapping> ConvertNSDataToMappingPtr(NSData* data);
 
 NSData* CopyMappingPtrToNSData(std::unique_ptr<fml::Mapping> mapping);
 

shell/platform/darwin/common/buffer_conversions.mm

@@ -4,20 +4,38 @@
 
 #import "flutter/shell/platform/darwin/common/buffer_conversions.h"
 
+#include "flutter/fml/platform/darwin/scoped_nsobject.h"
+
 namespace flutter {
+namespace {
+class NSDataMapping : public fml::Mapping {
+ public:
+  NSDataMapping(NSData* data) : data_([data retain]) {}
+
+  size_t GetSize() const override { return [data_.get() length]; }
+
+  const uint8_t* GetMapping() const override {
+    return static_cast<const uint8_t*>([data_.get() bytes]);
+  }
+
+ private:
+  fml::scoped_nsobject<NSData> data_;
+  FML_DISALLOW_COPY_AND_ASSIGN(NSDataMapping);
+};
+}  // namespace
 
 fml::MallocMapping CopyNSDataToMapping(NSData* data) {
   const uint8_t* bytes = static_cast<const uint8_t*>(data.bytes);
   return fml::MallocMapping::Copy(bytes, data.length);
 }
 
-NSData* CopyMappingToNSData(fml::MallocMapping buffer) {
-  return [NSData dataWithBytes:const_cast<uint8_t*>(buffer.GetMapping()) length:buffer.GetSize()];
+NSData* ConvertMappingToNSData(fml::MallocMapping buffer) {
+  size_t size = buffer.GetSize();
+  return [NSData dataWithBytesNoCopy:const_cast<uint8_t*>(buffer.Release()) length:size];
 }
 
-std::unique_ptr<fml::Mapping> CopyNSDataToMappingPtr(NSData* data) {
-  auto mapping = CopyNSDataToMapping(data);
-  return std::make_unique<fml::MallocMapping>(std::move(mapping));
+std::unique_ptr<fml::Mapping> ConvertNSDataToMappingPtr(NSData* data) {
+  return std::make_unique<NSDataMapping>(data);
 }
 
 NSData* CopyMappingPtrToNSData(std::unique_ptr<fml::Mapping> mapping) {

shell/platform/darwin/ios/framework/Source/platform_message_router.mm

@@ -22,12 +22,12 @@
     FlutterBinaryMessageHandler handler = it->second;
     NSData* data = nil;
     if (message->hasData()) {
-      data = CopyMappingToNSData(message->releaseData());
+      data = ConvertMappingToNSData(message->releaseData());
     }
     handler(data, ^(NSData* reply) {
       if (completer) {
         if (reply) {
-          completer->Complete(CopyNSDataToMappingPtr(reply));
+          completer->Complete(ConvertNSDataToMappingPtr(reply));
         } else {
           completer->CompleteEmpty();
         }