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

// Copyright 2017 The Chromium Authors
// 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_UNSERIALIZED_MESSAGE_CONTEXT_H_
#define MOJO_PUBLIC_CPP_BINDINGS_LIB_UNSERIALIZED_MESSAGE_CONTEXT_H_

#include <stdint.h>

#include "base/component_export.h"
#include "mojo/public/cpp/bindings/lib/message_internal.h"

namespace mojo {
namespace internal {

class COMPONENT_EXPORT(MOJO_CPP_BINDINGS_BASE) UnserializedMessageContext {
 public:
  struct Tag {};

  UnserializedMessageContext(const Tag* tag,
                             uint32_t message_name,
                             uint32_t message_flags);

  UnserializedMessageContext(const UnserializedMessageContext&) = delete;
  UnserializedMessageContext& operator=(const UnserializedMessageContext&) =
      delete;

  virtual ~UnserializedMessageContext();

  template <typename MessageType>
  MessageType* SafeCast() {
    if (reinterpret_cast<uintptr_t>(&MessageType::kMessageTag) != tag_) {
      return nullptr;
    }
    return static_cast<MessageType*>(this);
  }

  uintptr_t tag() const { return tag_; }
  uint32_t message_name() const { return header_.name; }
  uint32_t message_flags() const { return header_.flags; }

  MessageHeaderV1* header() { return &header_; }

  virtual void Serialize(Message& message) = 0;

 private:
  // The |tag_| is used for run-time type identification of specific
  // unserialized message types, e.g. messages generated by mojom bindings. This
  // allows opaque message objects to be safely downcast once pulled off a pipe.
  const uintptr_t tag_;

  // We store message metadata in a serialized header structure to simplify
  // Message implementation which needs to query such metadata for both
  // serialized and unserialized message objects.
  MessageHeaderV1 header_;
};

}  // namespace internal
}  // namespace mojo

#endif  // MOJO_PUBLIC_CPP_BINDINGS_LIB_UNSERIALIZED_MESSAGE_CONTEXT_H_