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// Copyright 2013 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.
#include <stdint.h>
#include <stdlib.h> // For |free()|.
#include "base/basictypes.h"
#include "mojo/public/system/system_export.h"
namespace mojo {
namespace system {
// This class is used to represent data in transit. It is thread-unsafe.
// Note: This class is POD.
class MOJO_SYSTEM_EXPORT MessageInTransit {
typedef uint16_t Type;
// Messages that are forwarded to |MessagePipeEndpoint|s.
static const Type kTypeMessagePipeEndpoint = 0;
// Messages that are forwarded to |MessagePipe|s.
static const Type kTypeMessagePipe = 1;
// Messages that are consumed by the channel.
static const Type TYPE_CHANNEL = 2;
typedef uint16_t Subtype;
// Subtypes for type |kTypeMessagePipeEndpoint|:
static const Subtype kSubtypeMessagePipeEndpointData = 0;
// Subtypes for type |kTypeMessagePipe|:
static const Subtype kSubtypeMessagePipePeerClosed = 0;
typedef uint32_t EndpointId;
// Never a valid endpoint ID.
static const EndpointId kInvalidEndpointId = 0;
// Messages (the header and data) must always be aligned to a multiple of this
// quantity (which must be a power of 2).
static const size_t kMessageAlignment = 8;
// Creates a |MessageInTransit| of the given |type| and |subtype|, with the
// data given by |bytes|/|num_bytes|.
static MessageInTransit* Create(Type type, Subtype subtype,
const void* bytes, uint32_t num_bytes);
// Destroys a |MessageInTransit| created using |Create()|.
inline void Destroy() {
// No need to call the destructor, since we're POD.
// Gets the size of the data (in number of bytes).
uint32_t data_size() const {
return size_;
// Gets the data (of size |size()| bytes).
const void* data() const {
return reinterpret_cast<const char*>(this) + sizeof(*this);
size_t size_with_header_and_padding() const {
return RoundUpMessageAlignment(sizeof(*this) + size_);
Type type() const { return type_; }
Subtype subtype() const { return subtype_; }
EndpointId source_id() const { return source_id_; }
EndpointId destination_id() const { return destination_id_; }
void set_source_id(EndpointId source_id) { source_id_ = source_id; }
void set_destination_id(EndpointId destination_id) {
destination_id_ = destination_id;
// TODO(vtl): Add whatever's necessary to transport handles.
// Rounds |n| up to a multiple of |kMessageAlignment|.
static inline size_t RoundUpMessageAlignment(size_t n) {
return (n + kMessageAlignment - 1) & ~(kMessageAlignment - 1);
explicit MessageInTransit(uint32_t size, Type type, Subtype subtype)
: size_(size),
destination_id_(kInvalidEndpointId) {}
// "Header" for the data.
uint32_t size_;
Type type_;
Subtype subtype_;
EndpointId source_id_;
EndpointId destination_id_;
// Intentionally unimplemented (and private): Use |Destroy()| instead (which
// simply frees the memory).
// The size of |MessageInTransit| must be appropriate to maintain alignment of
// the following data.
COMPILE_ASSERT(sizeof(MessageInTransit) == 16, MessageInTransit_has_wrong_size);
} // namespace system
} // namespace mojo