Mojo C++ bindings: introduce an optional array to store transferred interface IDs in messages.

mojo/public/cpp/bindings/lib/message_internal.h

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef MOJO_PUBLIC_CPP_BINDINGS_LIB_MESSAGE_INTERNAL_H_
 #define MOJO_PUBLIC_CPP_BINDINGS_LIB_MESSAGE_INTERNAL_H_
 
 #include <stdint.h>
 
 #include <string>
 
 #include "base/callback.h"
 #include "base/macros.h"
 #include "mojo/public/cpp/bindings/bindings_export.h"
 #include "mojo/public/cpp/bindings/lib/bindings_internal.h"
 
 namespace mojo {
 
 class Message;
 
 namespace internal {
 
+template <typename T>
+class Array_Data;
+
 #pragma pack(push, 1)
 
 struct MessageHeader : internal::StructHeader {
   // Interface ID for identifying multiple interfaces running on the same
   // message pipe.
   uint32_t interface_id;
   // Message name, which is scoped to the interface that the message belongs to.
   uint32_t name;
   // 0 or either of the enum values defined above.
   uint32_t flags;
   // Unused padding to make the struct size a multiple of 8 bytes.
   uint32_t padding;
 };
 static_assert(sizeof(MessageHeader) == 24, "Bad sizeof(MessageHeader)");
 
-struct MessageHeaderWithRequestID : MessageHeader {
+struct MessageHeaderV1 : MessageHeader {
   // Only used if either kFlagExpectsResponse or kFlagIsResponse is set in
   // order to match responses with corresponding requests.
   uint64_t request_id;
 };
-static_assert(sizeof(MessageHeaderWithRequestID) == 32,
-              "Bad sizeof(MessageHeaderWithRequestID)");
+static_assert(sizeof(MessageHeaderV1) == 32, "Bad sizeof(MessageHeaderV1)");
+
+struct MessageHeaderV2 : MessageHeaderV1 {
+  MessageHeaderV2();
+  GenericPointer payload;
+  Pointer<Array_Data<uint32_t>> payload_interface_ids;
+};
+static_assert(sizeof(MessageHeaderV2) == 48, "Bad sizeof(MessageHeaderV2)");
 
 #pragma pack(pop)
 
 class MOJO_CPP_BINDINGS_EXPORT MessageDispatchContext {
  public:
   explicit MessageDispatchContext(Message* message);
   ~MessageDispatchContext();
 
   static MessageDispatchContext* current();
 
   const base::Callback<void(const std::string&)>& GetBadMessageCallback();
 
  private:
   MessageDispatchContext* outer_context_;
   Message* message_;
   base::Callback<void(const std::string&)> bad_message_callback_;
 
   DISALLOW_COPY_AND_ASSIGN(MessageDispatchContext);
 };
 
 class MOJO_CPP_BINDINGS_EXPORT SyncMessageResponseSetup {
  public:
   static void SetCurrentSyncResponseMessage(Message* message);
 };
 
 }  // namespace internal
 }  // namespace mojo
 
 #endif  // MOJO_PUBLIC_CPP_BINDINGS_LIB_MESSAGE_INTERNAL_H_