Even though the file is pure C code, it's useful to use a C++ or Objective-C++ filename in order to use FML (assertions) in the implementation.

Three implementation changes:
* Since the file is now C++, some implicit void* conversions now require
  an explicit cast.
* A malloc/free of a buffer has been replaced with a std::vector.
* An `assert()` was changed to `FML_DCHECK` for consistency with the
  rest of the embedder.

No test changes since there are no semantic changes.

Existing tests are in:
https://github.com/flutter/engine/blob/main/shell/platform/darwin/common/framework/Source/flutter_standard_codec_unittest.mm

Author: cbracken

ci/licenses_golden/licenses_flutter

@@ -2417,7 +2417,7 @@ ORIGIN: ../../../flutter/shell/platform/darwin/common/framework/Source/FlutterCh
 ORIGIN: ../../../flutter/shell/platform/darwin/common/framework/Source/FlutterChannelsTest.m + ../../../flutter/LICENSE
 ORIGIN: ../../../flutter/shell/platform/darwin/common/framework/Source/FlutterCodecs.mm + ../../../flutter/LICENSE
 ORIGIN: ../../../flutter/shell/platform/darwin/common/framework/Source/FlutterStandardCodec.mm + ../../../flutter/LICENSE
-ORIGIN: ../../../flutter/shell/platform/darwin/common/framework/Source/FlutterStandardCodecHelper.c + ../../../flutter/LICENSE
+ORIGIN: ../../../flutter/shell/platform/darwin/common/framework/Source/FlutterStandardCodecHelper.cc + ../../../flutter/LICENSE
 ORIGIN: ../../../flutter/shell/platform/darwin/common/framework/Source/FlutterStandardCodecHelper.h + ../../../flutter/LICENSE
 ORIGIN: ../../../flutter/shell/platform/darwin/common/framework/Source/FlutterStandardCodec_Internal.h + ../../../flutter/LICENSE
 ORIGIN: ../../../flutter/shell/platform/darwin/graphics/FlutterDarwinContextMetalImpeller.h + ../../../flutter/LICENSE
@@ -4874,7 +4874,7 @@ FILE: ../../../flutter/shell/platform/darwin/common/framework/Source/FlutterChan
 FILE: ../../../flutter/shell/platform/darwin/common/framework/Source/FlutterChannelsTest.m
 FILE: ../../../flutter/shell/platform/darwin/common/framework/Source/FlutterCodecs.mm
 FILE: ../../../flutter/shell/platform/darwin/common/framework/Source/FlutterStandardCodec.mm
-FILE: ../../../flutter/shell/platform/darwin/common/framework/Source/FlutterStandardCodecHelper.c
+FILE: ../../../flutter/shell/platform/darwin/common/framework/Source/FlutterStandardCodecHelper.cc
 FILE: ../../../flutter/shell/platform/darwin/common/framework/Source/FlutterStandardCodecHelper.h
 FILE: ../../../flutter/shell/platform/darwin/common/framework/Source/FlutterStandardCodec_Internal.h
 FILE: ../../../flutter/shell/platform/darwin/graphics/FlutterDarwinContextMetalImpeller.h

shell/platform/darwin/BUILD.gn

@@ -47,7 +47,7 @@ source_set("flutter_channels_arc") {
     "common/framework/Source/FlutterChannels.mm",
     "common/framework/Source/FlutterCodecs.mm",
     "common/framework/Source/FlutterStandardCodec.mm",
-    "common/framework/Source/FlutterStandardCodecHelper.c",
+    "common/framework/Source/FlutterStandardCodecHelper.cc",
     "common/framework/Source/FlutterStandardCodec_Internal.h",
   ]
 
@@ -60,6 +60,8 @@ source_set("flutter_channels_arc") {
   ]
 
   public_configs = [ "//flutter:config" ]
+
+  deps = [ "//flutter/fml" ]
 }
 
 test_fixtures("flutter_channels_fixtures") {

shell/platform/darwin/common/BUILD.gn

@@ -37,7 +37,7 @@ source_set("framework_shared") {
     "framework/Source/FlutterChannels.mm",
     "framework/Source/FlutterCodecs.mm",
     "framework/Source/FlutterStandardCodec.mm",
-    "framework/Source/FlutterStandardCodecHelper.c",
+    "framework/Source/FlutterStandardCodecHelper.cc",
     "framework/Source/FlutterStandardCodec_Internal.h",
   ]
 
@@ -49,4 +49,6 @@ source_set("framework_shared") {
     "//flutter:config",
     ":framework_relative_headers",
   ]
+
+  deps = [ "//flutter/fml" ]
 }

shell/platform/darwin/common/framework/Source/FlutterStandardCodecHelper.c renamed to shell/platform/darwin/common/framework/Source/FlutterStandardCodecHelper.cc

@@ -5,6 +5,16 @@
 #include "flutter/shell/platform/darwin/common/framework/Source/FlutterStandardCodecHelper.h"
 #include <stdint.h>
 
+#include <vector>
+
+#include "flutter/fml/logging.h"
+
+// The google-runtime-int lint suggests uint64_t in place of unsigned long,
+// however these functions are frequently used with NSUInteger, which is
+// defined as an unsigned long.
+//
+// NOLINTBEGIN(google-runtime-int)
+
 void FlutterStandardCodecHelperReadAlignment(unsigned long* location,
                                              uint8_t alignment) {
   uint8_t mod = *location % alignment;
@@ -25,7 +35,7 @@ void FlutterStandardCodecHelperReadBytes(unsigned long* location,
                                          void* destination,
                                          CFDataRef data) {
   CFRange range = CFRangeMake(*location, length);
-  CFDataGetBytes(data, range, destination);
+  CFDataGetBytes(data, range, static_cast<UInt8*>(destination));
   *location += length;
 }
 
@@ -59,7 +69,7 @@ static CFDataRef ReadDataNoCopy(unsigned long* location,
       kCFAllocatorDefault, CFDataGetBytePtr(data) + *location, length,
       kCFAllocatorNull);
   *location += length;
-  return CFAutorelease(result);
+  return static_cast<CFDataRef>(CFAutorelease(result));
 }
 
 CFStringRef FlutterStandardCodecHelperReadUTF8(unsigned long* location,
@@ -68,7 +78,7 @@ CFStringRef FlutterStandardCodecHelperReadUTF8(unsigned long* location,
   CFDataRef bytes = ReadDataNoCopy(location, size, data);
   CFStringRef result = CFStringCreateFromExternalRepresentation(
       kCFAllocatorDefault, bytes, kCFStringEncodingUTF8);
-  return CFAutorelease(result);
+  return static_cast<CFStringRef>(CFAutorelease(result));
 }
 
 // Peeks ahead to see if we are reading a standard type.  If so, recurse
@@ -161,7 +171,7 @@ CFTypeRef FlutterStandardCodecHelperReadValueOfType(
     }
     default:
       // Malformed message.
-      assert(false);
+      FML_DCHECK(false);
   }
 }
 
@@ -172,7 +182,7 @@ void FlutterStandardCodecHelperWriteByte(CFMutableDataRef data, uint8_t value) {
 void FlutterStandardCodecHelperWriteBytes(CFMutableDataRef data,
                                           const void* bytes,
                                           unsigned long length) {
-  CFDataAppendBytes(data, bytes, length);
+  CFDataAppendBytes(data, static_cast<const UInt8*>(bytes), length);
 }
 
 void FlutterStandardCodecHelperWriteSize(CFMutableDataRef data, uint32_t size) {
@@ -210,12 +220,12 @@ void FlutterStandardCodecHelperWriteUTF8(CFMutableDataRef data,
     CFIndex used_length = 0;
     // UTF16 length times 3 will fit all UTF8.
     CFIndex buffer_length = length * 3;
-    UInt8* buffer = (UInt8*)malloc(buffer_length * sizeof(UInt8));
+    std::vector<UInt8> buffer;
+    buffer.reserve(buffer_length);
     CFStringGetBytes(value, CFRangeMake(0, length), kCFStringEncodingUTF8, 0,
-                     false, buffer, buffer_length, &used_length);
+                     false, buffer.data(), buffer_length, &used_length);
     FlutterStandardCodecHelperWriteSize(data, used_length);
-    FlutterStandardCodecHelperWriteBytes(data, buffer, used_length);
-    free(buffer);
+    FlutterStandardCodecHelperWriteBytes(data, buffer.data(), used_length);
   }
 }
 
@@ -259,3 +269,5 @@ bool FlutterStandardCodecHelperWriteNumber(CFMutableDataRef data,
   }
   return success;
 }
+
+// NOLINTEND(google-runtime-int)