Mojo: Use new message APIs to reduce copying

mojo/public/cpp/system/message.h

+// Copyright 2016 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_SYSTEM_MESSAGE_H_
+#define MOJO_PUBLIC_CPP_SYSTEM_MESSAGE_H_
+
+#include <limits>
+
+#include "base/macros.h"
+#include "mojo/public/c/system/message_pipe.h"
+#include "mojo/public/cpp/system/handle.h"
+
+namespace mojo {
+
+const MojoMessageHandle kInvalidMessageHandleValue =
+    MOJO_MESSAGE_HANDLE_INVALID;
+
+// Handle wrapper base class for a |MojoMessageHandle|.
+class MessageHandle {
+ public:
+  MessageHandle() : value_(kInvalidMessageHandleValue) {}
+  explicit MessageHandle(MojoMessageHandle value) : value_(value) {}
+  ~MessageHandle() {}
+
+  void swap(MessageHandle& other) {
+    MojoMessageHandle temp = value_;
+    value_ = other.value_;
+    other.value_ = temp;
+  }
+
+  bool is_valid() const { return value_ != kInvalidMessageHandleValue; }
+
+  const MojoMessageHandle& value() const { return value_; }
+  MojoMessageHandle* mutable_value() { return &value_; }
+  void set_value(MojoMessageHandle value) { value_ = value; }
+
+  void Close() {
+    DCHECK(is_valid());
+    MojoResult result = MojoFreeMessage(value_);
+    ALLOW_UNUSED_LOCAL(result);
+    DCHECK_EQ(MOJO_RESULT_OK, result);
+  }
+
+ private:
+  MojoMessageHandle value_;
+};
+
+using ScopedMessageHandle = ScopedHandleBase<MessageHandle>;
+
+inline MojoResult AllocMessage(size_t num_bytes,
+                               const MojoHandle* handles,
+                               size_t num_handles,
+                               MojoAllocMessageFlags flags,
+                               ScopedMessageHandle* handle) {
+  DCHECK_LE(num_bytes, std::numeric_limits<uint32_t>::max());
+  DCHECK_LE(num_handles, std::numeric_limits<uint32_t>::max());
+  MojoMessageHandle raw_handle;
+  MojoResult rv = MojoAllocMessage(static_cast<uint32_t>(num_bytes), handles,
+                                   static_cast<uint32_t>(num_handles), flags,
+                                   &raw_handle);
+  if (rv != MOJO_RESULT_OK)
+    return rv;
+
+  handle->reset(MessageHandle(raw_handle));
+  return MOJO_RESULT_OK;
+}
+
+inline MojoResult GetMessageBuffer(MessageHandle message, void** buffer) {
+  DCHECK(message.is_valid());
+  return MojoGetMessageBuffer(message.value(), buffer);
+}
+
+}  // namespace mojo
+
+#endif  // MOJO_PUBLIC_CPP_SYSTEM_MESSAGE_H_