ipc/ipc_channel_posix.h

   1 // Copyright (c) 2011 The Chromium Authors. All rights reserved.
   2 // Use of this source code is governed by a BSD-style license that can be
   3 // found in the LICENSE file.
   4
   5 #ifndef IPC_IPC_CHANNEL_POSIX_H_
   6 #define IPC_IPC_CHANNEL_POSIX_H_
   7 #pragma once
   8
   9 #include "ipc/ipc_channel.h"
  10
  11 #include <sys/socket.h>  // for CMSG macros
  12
  13 #include <queue>
  14 #include <string>
  15 #include <vector>
  16
  17 #include "base/message_loop.h"
  18 #include "ipc/file_descriptor_set_posix.h"
  19
  20 #if !defined(OS_MACOSX)
  21 // On Linux, the seccomp sandbox makes it very expensive to call
  22 // recvmsg() and sendmsg(). The restriction on calling read() and write(), which
  23 // are cheap, is that we can't pass file descriptors over them.
  24 //
  25 // As we cannot anticipate when the sender will provide us with file
  26 // descriptors, we have to make the decision about whether we call read() or
  27 // recvmsg() before we actually make the call. The easiest option is to
  28 // create a dedicated socketpair() for exchanging file descriptors. Any file
  29 // descriptors are split out of a message, with the non-file-descriptor payload
  30 // going over the normal connection, and the file descriptors being sent
  31 // separately over the other channel. When read()ing from a channel, we'll
  32 // notice if the message was supposed to have come with file descriptors and
  33 // use recvmsg on the other socketpair to retrieve them and combine them
  34 // back with the rest of the message.
  35 //
  36 // Mac can also run in IPC_USES_READWRITE mode if necessary, but at this time
  37 // doesn't take a performance hit from recvmsg and sendmsg, so it doesn't
  38 // make sense to waste resources on having the separate dedicated socketpair.
  39 // It is however useful for debugging between Linux and Mac to be able to turn
  40 // this switch 'on' on the Mac as well.
  41 //
  42 // The HELLO message from the client to the server is always sent using
  43 // sendmsg because it will contain the file descriptor that the server
  44 // needs to send file descriptors in later messages.
  45 #define IPC_USES_READWRITE 1
  46 #endif
  47
  48 namespace IPC {
  49
  50 class Channel::ChannelImpl : public MessageLoopForIO::Watcher {
  51  public:
  52   // Mirror methods of Channel, see ipc_channel.h for description.
  53   ChannelImpl(const IPC::ChannelHandle& channel_handle, Mode mode,
  54               Listener* listener);
  55   virtual ~ChannelImpl();
  56   bool Connect();
  57   void Close();
  58   void set_listener(Listener* listener) { listener_ = listener; }
  59   bool Send(Message* message);
  60   int GetClientFileDescriptor() const;
  61   bool AcceptsConnections() const;
  62   bool HasAcceptedConnection() const;
  63   bool GetClientEuid(uid_t* client_euid) const;
  64   void ResetToAcceptingConnectionState();
  65
  66  private:
  67   bool CreatePipe(const IPC::ChannelHandle& channel_handle);
  68
  69   bool ProcessIncomingMessages();
  70   bool ProcessOutgoingMessages();
  71
  72   bool AcceptConnection();
  73   void ClosePipeOnError();
  74   void QueueHelloMessage();
  75   bool IsHelloMessage(const Message* m) const;
  76
  77   // MessageLoopForIO::Watcher implementation.
  78   virtual void OnFileCanReadWithoutBlocking(int fd);
  79   virtual void OnFileCanWriteWithoutBlocking(int fd);
  80
  81   Mode mode_;
  82
  83   // After accepting one client connection on our server socket we want to
  84   // stop listening.
  85   MessageLoopForIO::FileDescriptorWatcher server_listen_connection_watcher_;
  86   MessageLoopForIO::FileDescriptorWatcher read_watcher_;
  87   MessageLoopForIO::FileDescriptorWatcher write_watcher_;
  88
  89   // Indicates whether we're currently blocked waiting for a write to complete.
  90   bool is_blocked_on_write_;
  91   bool waiting_connect_;
  92
  93   // If sending a message blocks then we use this variable
  94   // to keep track of where we are.
  95   size_t message_send_bytes_written_;
  96
  97   // File descriptor we're listening on for new connections if we listen
  98   // for connections.
  99   int server_listen_pipe_;
 100
 101   // The pipe used for communication.
 102   int pipe_;
 103
 104   // For a server, the client end of our socketpair() -- the other end of our
 105   // pipe_ that is passed to the client.
 106   int client_pipe_;
 107
 108 #if defined(IPC_USES_READWRITE)
 109   // Linux/BSD use a dedicated socketpair() for passing file descriptors.
 110   int fd_pipe_;
 111   int remote_fd_pipe_;
 112 #endif
 113
 114   // The "name" of our pipe.  On Windows this is the global identifier for
 115   // the pipe.  On POSIX it's used as a key in a local map of file descriptors.
 116   std::string pipe_name_;
 117
 118   Listener* listener_;
 119
 120   // Messages to be sent are queued here.
 121   std::queue<Message*> output_queue_;
 122
 123   // We read from the pipe into this buffer
 124   char input_buf_[Channel::kReadBufferSize];
 125
 126   enum {
 127     // We assume a worst case: kReadBufferSize bytes of messages, where each
 128     // message has no payload and a full complement of descriptors.
 129     MAX_READ_FDS = (Channel::kReadBufferSize / sizeof(IPC::Message::Header)) *
 130                    FileDescriptorSet::MAX_DESCRIPTORS_PER_MESSAGE,
 131   };
 132
 133   // This is a control message buffer large enough to hold kMaxReadFDs
 134 #if defined(OS_MACOSX)
 135   // TODO(agl): OSX appears to have non-constant CMSG macros!
 136   char input_cmsg_buf_[1024];
 137 #else
 138   char input_cmsg_buf_[CMSG_SPACE(sizeof(int) * MAX_READ_FDS)];
 139 #endif
 140
 141   // Large messages that span multiple pipe buffers, get built-up using
 142   // this buffer.
 143   std::string input_overflow_buf_;
 144   std::vector<int> input_overflow_fds_;
 145
 146   // True if we are responsible for unlinking the unix domain socket file.
 147   bool must_unlink_;
 148
 149   DISALLOW_IMPLICIT_CONSTRUCTORS(ChannelImpl);
 150 };
 151
 152 // The maximum length of the name of a pipe for MODE_NAMED_SERVER or
 153 // MODE_NAMED_CLIENT if you want to pass in your own socket.
 154 // The standard size on linux is 108, mac is 104. To maintain consistency
 155 // across platforms we standardize on the smaller value.
 156 static const size_t kMaxPipeNameLength = 104;
 157
 158 }  // namespace IPC
 159
 160 #endif  // IPC_IPC_CHANNEL_POSIX_H_