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// 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.
#include <vector>
#include "base/containers/span.h"
#include "base/macros.h"
#include "base/memory/ref_counted.h"
#include "base/process/process_handle.h"
#include "base/task_runner.h"
#include "build/build_config.h"
#include "mojo/core/connection_params.h"
#include "mojo/core/platform_handle_in_transit.h"
#include "mojo/core/scoped_process_handle.h"
#include "mojo/public/cpp/platform/platform_handle.h"
namespace mojo {
namespace core {
const size_t kChannelMessageAlignment = 8;
constexpr bool IsAlignedForChannelMessage(size_t n) {
return n % kChannelMessageAlignment == 0;
// Channel provides a thread-safe interface to read and write arbitrary
// delimited messages over an underlying I/O channel, optionally transferring
// one or more platform handles in the process.
: public base::RefCountedThreadSafe<Channel> {
enum class HandlePolicy {
// If a Channel is constructed in this mode, it will accept messages with
// platform handle attachements.
// If a Channel is constructed in this mode, it will reject messages with
// platform handle attachments and treat them as malformed messages.
enum class DispatchBufferPolicy {
// If the Channel is constructed in this mode, it will create and manage a
// buffer that implementations should manipulate with GetReadBuffer() and
// OnReadComplete().
// If the Channel is constructed in this mode, it will not create and
// manage a buffer for the implementation. Instead, the implementation must
// use its own buffer and pass spans of it to TryDispatchMessage().
struct Message;
using MessagePtr = std::unique_ptr<Message>;
// A message to be written to a channel.
enum class MessageType : uint16_t {
// An old format normal message, that uses the LegacyHeader.
// Only used on Android and ChromeOS.
// TODO( remove legacy support when Arc++ has
// updated to Mojo with normal versioned messages.
#if defined(OS_MACOSX)
// A control message containing handles to echo back.
// A control message containing handles that can now be closed.
// A normal message that uses Header and can contain extra header values.
#pragma pack(push, 1)
// Old message wire format for ChromeOS and Android, used by NORMAL_LEGACY
// messages.
struct LegacyHeader {
// Message size in bytes, including the header.
uint32_t num_bytes;
// Number of attached handles.
uint16_t num_handles;
MessageType message_type;
// Header used by NORMAL messages.
// To preserve backward compatibility with LegacyHeader, the num_bytes and
// message_type field must be at the same offset as in LegacyHeader.
struct Header {
// Message size in bytes, including the header.
uint32_t num_bytes;
// Total size of header, including extra header data (i.e. HANDLEs on
// windows).
uint16_t num_header_bytes;
MessageType message_type;
// Number of attached handles. May be less than the reserved handle
// storage size in this message on platforms that serialise handles as
// data (i.e. HANDLEs on Windows, Mach ports on OSX).
uint16_t num_handles;
char padding[6];
#if defined(OS_MACOSX) && !defined(OS_IOS)
union MachPortsEntry {
// Used with ChannelPosix.
struct {
// Index of Mach port in the original vector of
// PlatformHandleInTransits.
uint16_t index;
// Mach port name.
uint32_t mach_port;
} posix_entry;
// Used with ChannelMac.
struct {
// The PlatformHandle::Type.
uint8_t type;
} mach_entry;
static_assert(sizeof(mach_port_t) <= sizeof(uint32_t),
"mach_port_t must be no larger than uint32_t");
static_assert(sizeof(MachPortsEntry) == 6,
"sizeof(MachPortsEntry) must be 6 bytes");
// Structure of the extra header field when present on OSX.
struct MachPortsExtraHeader {
// Actual number of Mach ports encoded in the extra header.
uint16_t num_ports;
// Array of encoded Mach ports. If |num_ports| > 0, |entries[0]| through
// to |entries[num_ports-1]| inclusive are valid.
MachPortsEntry entries[0];
static_assert(sizeof(MachPortsExtraHeader) == 2,
"sizeof(MachPortsExtraHeader) must be 2 bytes");
#elif defined(OS_FUCHSIA)
struct HandleInfoEntry {
// True if the handle represents an FDIO file-descriptor, false otherwise.
bool is_file_descriptor;
#elif defined(OS_WIN)
struct HandleEntry {
// The windows HANDLE. HANDLEs are guaranteed to fit inside 32-bits.
// See:
uint32_t handle;
static_assert(sizeof(HandleEntry) == 4,
"sizeof(HandleEntry) must be 4 bytes");
#pragma pack(pop)
// Allocates and owns a buffer for message data with enough capacity for
// |payload_size| bytes plus a header, plus |max_handles| platform handles.
Message(size_t payload_size, size_t max_handles);
Message(size_t payload_size, size_t max_handles, MessageType message_type);
Message(size_t capacity, size_t payload_size, size_t max_handles);
Message(size_t capacity,
size_t max_handles,
size_t payload_size,
MessageType message_type);
static MessagePtr CreateRawForFuzzing(base::span<const unsigned char> data);
// Constructs a Message from serialized message data, optionally coming from
// a known remote process.
static MessagePtr Deserialize(
const void* data,
size_t data_num_bytes,
base::ProcessHandle from_process = base::kNullProcessHandle);
const void* data() const { return data_; }
size_t data_num_bytes() const { return size_; }
// The current capacity of the message buffer, not counting internal header
// data.
size_t capacity() const;
// Extends the portion of the total message capacity which contains
// meaningful payload data. Storage capacity which falls outside of this
// range is not transmitted when the message is sent.
// If the message's current capacity is not large enough to accommodate the
// new payload size, it will be reallocated accordingly.
void ExtendPayload(size_t new_payload_size);
const void* extra_header() const;
void* mutable_extra_header();
size_t extra_header_size() const;
void* mutable_payload();
const void* payload() const;
size_t payload_size() const;
size_t num_handles() const;
bool has_handles() const;
#if defined(OS_MACOSX) && !defined(OS_IOS)
bool has_mach_ports() const;
bool is_legacy_message() const;
LegacyHeader* legacy_header() const;
Header* header() const;
// Note: SetHandles() and TakeHandles() invalidate any previous value of
// handles().
void SetHandles(std::vector<PlatformHandle> new_handles);
void SetHandles(std::vector<PlatformHandleInTransit> new_handles);
std::vector<PlatformHandleInTransit> TakeHandles();
// Version of TakeHandles that returns a vector of platform handles suitable
// for transfer over an underlying OS mechanism. i.e. file descriptors over
// a unix domain socket. Any handle that cannot be transferred this way,
// such as Mach ports, will be removed.
std::vector<PlatformHandleInTransit> TakeHandlesForTransport();
void SetVersionForTest(uint16_t version_number);
// The message data buffer.
char* data_ = nullptr;
// The capacity of the buffer at |data_|.
size_t capacity_ = 0;
// The size of the message. This is the portion of |data_| that should
// be transmitted if the message is written to a channel. Includes all
// headers and user payload.
size_t size_ = 0;
// Maximum number of handles which may be attached to this message.
size_t max_handles_ = 0;
std::vector<PlatformHandleInTransit> handle_vector_;
#if defined(OS_WIN)
// On Windows, handles are serialised into the extra header section.
HandleEntry* handles_ = nullptr;
#elif defined(OS_MACOSX) && !defined(OS_IOS)
// On OSX, handles are serialised into the extra header section.
MachPortsExtraHeader* mach_ports_header_ = nullptr;
// Error types which may be reported by a Channel instance to its delegate.
enum class Error {
// The remote end of the channel has been closed, either explicitly or
// because the process which hosted it is gone.
// For connection-oriented channels (e.g. named pipes), an unexpected error
// occurred during channel connection.
// Some incoming data failed validation, implying either a buggy or
// compromised sender.
// Delegate methods are called from the I/O task runner with which the Channel
// was created (see Channel::Create).
class Delegate {
virtual ~Delegate() {}
// Notify of a received message. |payload| is not owned and must not be
// retained; it will be null if |payload_size| is 0. |handles| are
// transferred to the callee.
virtual void OnChannelMessage(const void* payload,
size_t payload_size,
std::vector<PlatformHandle> handles) = 0;
// Notify that an error has occured and the Channel will cease operation.
virtual void OnChannelError(Error error) = 0;
// Creates a new Channel around a |platform_handle|, taking ownership of the
// handle. All I/O on the handle will be performed on |io_task_runner|.
// Note that ShutDown() MUST be called on the Channel some time before
// |delegate| is destroyed.
static scoped_refptr<Channel> Create(
Delegate* delegate,
ConnectionParams connection_params,
HandlePolicy handle_policy,
scoped_refptr<base::TaskRunner> io_task_runner);
// Allows the caller to change the Channel's HandlePolicy after construction.
void set_handle_policy(HandlePolicy policy) { handle_policy_ = policy; }
// Request that the channel be shut down. This should always be called before
// releasing the last reference to a Channel to ensure that it's cleaned up
// on its I/O task runner's thread.
// Delegate methods will no longer be invoked after this call.
void ShutDown();
// Sets the process handle of the remote endpoint to which this Channel is
// connected. If called at all, must be called only once, and before Start().
void set_remote_process(ScopedProcessHandle remote_process) {
remote_process_ = std::move(remote_process);
const ScopedProcessHandle& remote_process() const { return remote_process_; }
// Begin processing I/O events. Delegate methods must only be invoked after
// this call.
virtual void Start() = 0;
// Stop processing I/O events.
virtual void ShutDownImpl() = 0;
// Queues an outgoing message on the Channel. This message will either
// eventually be written or will fail to write and trigger
// Delegate::OnChannelError.
virtual void Write(MessagePtr message) = 0;
// Causes the platform handle to leak when this channel is shut down instead
// of closing it.
virtual void LeakHandle() = 0;
// Constructor for implementations to call. |delegate| and |handle_policy|
// should be passed from Create(). |buffer_policy| should be specified by
// the implementation.
Channel(Delegate* delegate,
HandlePolicy handle_policy,
DispatchBufferPolicy buffer_policy = DispatchBufferPolicy::kManaged);
virtual ~Channel();
Delegate* delegate() const { return delegate_; }
// Called by the implementation when it wants somewhere to stick data.
// |*buffer_capacity| may be set by the caller to indicate the desired buffer
// size. If 0, a sane default size will be used instead.
// Returns the address of a buffer which can be written to, and indicates its
// actual capacity in |*buffer_capacity|.
// This should only be used with DispatchBufferPolicy::kManaged.
char* GetReadBuffer(size_t* buffer_capacity);
// Called by the implementation when new data is available in the read
// buffer. Returns false to indicate an error. Upon success,
// |*next_read_size_hint| will be set to a recommended size for the next
// read done by the implementation. This should only be used with
// DispatchBufferPolicy::kManaged.
bool OnReadComplete(size_t bytes_read, size_t* next_read_size_hint);
// Called by the implementation to deserialize a message stored in |buffer|.
// If the channel was created with DispatchBufferPolicy::kUnmanaged, the
// implementation should call this directly. If it was created with kManaged,
// OnReadComplete() will call this. |*size_hint| will be set to a recommended
// size for the next read done by the implementation.
enum class DispatchResult {
// The message was dispatched and consumed. |size_hint| contains the size
// of the message.
// The message could not be deserialized because |buffer| does not contain
// enough data. |size_hint| contains the amount of data missing.
// The message has associated handles that were not transferred in this
// message.
// An error occurred during processing.
DispatchResult TryDispatchMessage(base::span<const char> buffer,
size_t* size_hint);
// Called by the implementation when something goes horribly wrong. It is NOT
// OK to call this synchronously from any public interface methods.
void OnError(Error error);
// Retrieves the set of platform handles read for a given message.
// |extra_header| and |extra_header_size| correspond to the extra header data.
// Depending on the Channel implementation, this body may encode platform
// handles, or handles may be stored and managed elsewhere by the
// implementation.
// Returns |false| on unrecoverable error (i.e. the Channel should be closed).
// Returns |true| otherwise. Note that it is possible on some platforms for an
// insufficient number of handles to be available when this call is made, but
// this is not necessarily an error condition. In such cases this returns
// |true| but |*handles| will also be reset to null.
// If the implementation sets |*deferred| to |true|, it assumes responsibility
// for dispatching the message eventually. It must copy |payload| to retain
// it for later transmission.
virtual bool GetReadPlatformHandles(const void* payload,
size_t payload_size,
size_t num_handles,
const void* extra_header,
size_t extra_header_size,
std::vector<PlatformHandle>* handles,
bool* deferred) = 0;
// Handles a received control message. Returns |true| if the message is
// accepted, or |false| otherwise.
virtual bool OnControlMessage(Message::MessageType message_type,
const void* payload,
size_t payload_size,
std::vector<PlatformHandle> handles);
friend class base::RefCountedThreadSafe<Channel>;
class ReadBuffer;
Delegate* delegate_;
HandlePolicy handle_policy_;
const std::unique_ptr<ReadBuffer> read_buffer_;
// Handle to the process on the other end of this Channel, iff known.
ScopedProcessHandle remote_process_;
} // namespace core
} // namespace mojo