IPC: Add MojoHandleAttachment

ipc/mojo/ipc_mojo_handle_attachment.h

+// Copyright (c) 2015 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 IPC_MOJO_IPC_MOJO_HANDLE_ATTACHMENT_H_
+#define IPC_MOJO_IPC_MOJO_HANDLE_ATTACHMENT_H_
+
+#include "base/files/file.h"
+#include "ipc/ipc_export.h"
+#include "ipc/ipc_message_attachment.h"
+#include "third_party/mojo/src/mojo/public/cpp/system/handle.h"
+
+namespace IPC {
+
+namespace internal {
+
+// A MessageAttachment that holds a MojoHandle.
+// * On the sending side, every Mojo handle is a MessagePipe. This is because
+//   any platform files are wrapped by PlatformFileAttachment.
+// * On the receiving side, the handle can be either MessagePipe or wrapped
+//   platform file: All files, not only MessagePipes are wrapped as a
+//   MojoHandle. The message deserializer should know which type of the object
+//   the handle wraps.
+class IPC_MOJO_EXPORT MojoHandleAttachment : public MessageAttachment {
+ public:
+  explicit MojoHandleAttachment(mojo::ScopedHandle handle);
+
+  Type GetType() const override;
+
+#if defined(OS_POSIX)
+  // Returns wrapped file if it wraps a file, or
+  // an invalid fd otherwise. The ownership of handle
+  // is passed to the caller.
+  base::PlatformFile TakePlatformFile() override;
+#endif  // OS_POSIX
+
+  // Returns the owning handle transferring the ownership.
+  mojo::ScopedHandle TakeHandle();
+
+ private:
+  ~MojoHandleAttachment() override;
+  mojo::ScopedHandle handle_;
+
+  DISALLOW_COPY_AND_ASSIGN(MojoHandleAttachment);
+};
+
+}  // namespace internal
+}  // namespace IPC
+
+#endif  // IPC_MOJO_IPC_MOJO_HANDLE_ATTACHMENT_H_