Dont break codegen barrier

include/grpc++/impl/codegen/async_unary_call.h

@@ -42,8 +42,6 @@
 #include <grpc++/impl/codegen/service_type.h>
 #include <grpc++/impl/codegen/status.h>
 
-extern "C" void* grpc_call_arena_alloc(grpc_call* call, size_t size);
-
 namespace grpc {
 
 class CompletionQueue;
@@ -69,7 +67,8 @@ class ClientAsyncResponseReader final
                                            const W& request) {
     Call call = channel->CreateCall(method, context, cq);
     ClientAsyncResponseReader* reader =
-        new (grpc_call_arena_alloc(call.call(), sizeof(*reader)))
+        new (g_core_codegen_interface->grpc_call_arena_alloc(call.call(),
+                                                             sizeof(*reader)))
             ClientAsyncResponseReader(call, context);
 
     reader->init_buf_.SendInitialMetadata(context->send_initial_metadata_,

include/grpc++/impl/codegen/core_codegen.h

@@ -66,6 +66,7 @@ class CoreCodegen : public CoreCodegenInterface {
 
   void grpc_call_ref(grpc_call* call) override;
   void grpc_call_unref(grpc_call* call) override;
+  virtual void* grpc_call_arena_alloc(grpc_call* call, size_t length) override;
 
   void grpc_byte_buffer_destroy(grpc_byte_buffer* bb) override;
 

include/grpc++/impl/codegen/core_codegen_interface.h

@@ -96,6 +96,7 @@ class CoreCodegenInterface {
 
   virtual void grpc_call_ref(grpc_call* call) = 0;
   virtual void grpc_call_unref(grpc_call* call) = 0;
+  virtual void* grpc_call_arena_alloc(grpc_call* call, size_t length) = 0;
 
   virtual grpc_slice grpc_empty_slice() = 0;
   virtual grpc_slice grpc_slice_malloc(size_t length) = 0;

src/cpp/common/core_codegen.cc

@@ -93,6 +93,9 @@ void CoreCodegen::grpc_byte_buffer_destroy(grpc_byte_buffer* bb) {
 
 void CoreCodegen::grpc_call_ref(grpc_call* call) { ::grpc_call_ref(call); }
 void CoreCodegen::grpc_call_unref(grpc_call* call) { ::grpc_call_unref(call); }
+void* CoreCodegen::grpc_call_arena_alloc(grpc_call* call, size_t length) {
+  return ::grpc_call_arena_alloc(call, length);
+}
 
 int CoreCodegen::grpc_byte_buffer_reader_init(grpc_byte_buffer_reader* reader,
                                               grpc_byte_buffer* buffer) {