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// Copyright (c) 2012 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 <string>
#if defined(OS_POSIX)
#include <sys/types.h>
#include "base/compiler_specific.h"
#include "base/files/scoped_file.h"
#include "base/process/process.h"
#include "ipc/ipc_channel_handle.h"
#include "ipc/ipc_message.h"
#include "ipc/ipc_sender.h"
namespace IPC {
class Listener;
// See
// for overview of IPC in Chromium.
// Channels are implemented using named pipes on Windows, and
// socket pairs (or in some special cases unix domain sockets) on POSIX.
// On Windows we access pipes in various processes by name.
// On POSIX we pass file descriptors to child processes and assign names to them
// in a lookup table.
// In general on POSIX we do not use unix domain sockets due to security
// concerns and the fact that they can leave garbage around the file system
// (MacOS does not support abstract named unix domain sockets).
// You can use unix domain sockets if you like on POSIX by constructing the
// the channel with the mode set to one of the NAMED modes. NAMED modes are
// currently used by automation and service processes.
class IPC_EXPORT Channel : public Sender {
// Security tests need access to the pipe handle.
friend class ChannelTest;
// Flags to test modes
enum ModeFlags {
#if defined(OS_POSIX)
MODE_OPEN_ACCESS_FLAG = 0x8, // Don't restrict access based on client UID.
// Some Standard Modes
// TODO(morrita): These are under deprecation work. You should use Create*()
// functions instead.
enum Mode {
#if defined(OS_POSIX)
// Messages internal to the IPC implementation are defined here.
// Uses Maximum value of message type (uint16), to avoid conflicting
// with normal message types, which are enumeration constants starting from 0.
enum {
// The Hello message is sent by the peer when the channel is connected.
// The message contains just the process id (pid).
// The message has a special routing_id (MSG_ROUTING_NONE)
// and type (HELLO_MESSAGE_TYPE).
HELLO_MESSAGE_TYPE = kuint16max,
// The CLOSE_FD_MESSAGE_TYPE is used in the IPC class to
// work around a bug in sendmsg() on Mac. When an FD is sent
// over the socket, a CLOSE_FD_MESSAGE is sent with hops = 2.
// The client will return the message with hops = 1, *after* it
// has received the message that contains the FD. When we
// receive it again on the sender side, we close the FD.
// The maximum message size in bytes. Attempting to receive a message of this
// size or bigger results in a channel error.
static const size_t kMaximumMessageSize = 128 * 1024 * 1024;
// Amount of data to read at once from the pipe.
static const size_t kReadBufferSize = 4 * 1024;
// Initialize a Channel.
// |channel_handle| identifies the communication Channel. For POSIX, if
// the file descriptor in the channel handle is != -1, the channel takes
// ownership of the file descriptor and will close it appropriately, otherwise
// it will create a new descriptor internally.
// |listener| receives a callback on the current thread for each newly
// received message.
// There are four type of modes how channels operate:
// - Server and named server: In these modes, the Channel is
// responsible for settingb up the IPC object
// - An "open" named server: It accepts connections from ANY client.
// The caller must then implement their own access-control based on the
// client process' user Id.
// - Client and named client: In these mode, the Channel merely
// connects to the already established IPC object.
// Each mode has its own Create*() API to create the Channel object.
// TODO(morrita): Replace CreateByModeForProxy() with one of above Create*().
static scoped_ptr<Channel> Create(
const IPC::ChannelHandle &channel_handle, Mode mode, Listener* listener);
static scoped_ptr<Channel> CreateClient(
const IPC::ChannelHandle &channel_handle, Listener* listener);
// Channels on Windows are named by default and accessible from other
// processes. On POSIX channels are anonymous by default and not accessible
// from other processes. Named channels work via named unix domain sockets.
// On Windows MODE_NAMED_SERVER is equivalent to MODE_SERVER and
// MODE_NAMED_CLIENT is equivalent to MODE_CLIENT.
static scoped_ptr<Channel> CreateNamedServer(
const IPC::ChannelHandle &channel_handle, Listener* listener);
static scoped_ptr<Channel> CreateNamedClient(
const IPC::ChannelHandle &channel_handle, Listener* listener);
#if defined(OS_POSIX)
// An "open" named server accepts connections from ANY client.
// The caller must then implement their own access-control based on the
// client process' user Id.
static scoped_ptr<Channel> CreateOpenNamedServer(
const IPC::ChannelHandle &channel_handle, Listener* listener);
static scoped_ptr<Channel> CreateServer(
const IPC::ChannelHandle &channel_handle, Listener* listener);
~Channel() override;
// Connect the pipe. On the server side, this will initiate
// waiting for connections. On the client, it attempts to
// connect to a pre-existing pipe. Note, calling Connect()
// will not block the calling thread and may complete
// asynchronously.
virtual bool Connect() WARN_UNUSED_RESULT = 0;
// Close this Channel explicitly. May be called multiple times.
// On POSIX calling close on an IPC channel that listens for connections will
// cause it to close any accepted connections, and it will stop listening for
// new connections. If you just want to close the currently accepted
// connection and listen for new ones, use ResetToAcceptingConnectionState.
virtual void Close() = 0;
// Get the process ID for the connected peer.
// Returns base::kNullProcessId if the peer is not connected yet. Watch out
// for race conditions. You can easily get a channel to another process, but
// if your process has not yet processed the "hello" message from the remote
// side, this will fail. You should either make sure calling this is either
// in response to a message from the remote side (which guarantees that it's
// been connected), or you wait for the "connected" notification on the
// listener.
virtual base::ProcessId GetPeerPID() const = 0;
// Get its own process id. This value is told to the peer.
virtual base::ProcessId GetSelfPID() const = 0;
// Overridden from ipc::Sender.
// Send a message over the Channel to the listener on the other end.
// |message| must be allocated using operator new. This object will be
// deleted once the contents of the Message have been sent.
bool Send(Message* message) override = 0;
// NaCl in Non-SFI mode runs on Linux directly, and the following functions
// compiled on Linux are also needed. Please see also comments in
// components/nacl_nonsfi.gyp for more details.
#if defined(OS_POSIX) && !defined(OS_NACL_SFI)
// On POSIX an IPC::Channel wraps a socketpair(), this method returns the
// FD # for the client end of the socket.
// This method may only be called on the server side of a channel.
// This method can be called on any thread.
virtual int GetClientFileDescriptor() const = 0;
// Same as GetClientFileDescriptor, but transfers the ownership of the
// file descriptor to the caller.
// This method can be called on any thread.
virtual base::ScopedFD TakeClientFileDescriptor() = 0;
// Returns true if a named server channel is initialized on the given channel
// ID. Even if true, the server may have already accepted a connection.
static bool IsNamedServerInitialized(const std::string& channel_id);
#if !defined(OS_NACL_SFI)
// Generates a channel ID that's non-predictable and unique.
static std::string GenerateUniqueRandomChannelID();
// Generates a channel ID that, if passed to the client as a shared secret,
// will validate that the client's authenticity. On platforms that do not
// require additional this is simply calls GenerateUniqueRandomChannelID().
// For portability the prefix should not include the \ character.
static std::string GenerateVerifiedChannelID(const std::string& prefix);
#if defined(OS_LINUX)
// Sandboxed processes live in a PID namespace, so when sending the IPC hello
// message from client to server we need to send the PID from the global
// PID namespace.
static void SetGlobalPid(int pid);
#if defined(OS_ANDROID)
// Most tests are single process and work the same on all platforms. However
// in some cases we want to test multi-process, and Android differs in that it
// can't 'exec' after forking. This callback resets any data in the forked
// process such that it acts similar to if it was exec'd, for tests.
static void NotifyProcessForkedForTesting();
#if defined(OS_POSIX)
// SocketPair() creates a pair of socket FDs suitable for using with
// IPC::Channel.
IPC_EXPORT bool SocketPair(int* fd1, int* fd2);
} // namespace IPC
#endif // IPC_IPC_CHANNEL_H_