static void
check_read_watch (DBusTransport *transport)
{
  DBusTransportSocket *socket_transport = (DBusTransportSocket*) transport;
  dbus_bool_t need_read_watch;

  _dbus_verbose ("fd = %" DBUS_SOCKET_FORMAT "\n",
                 _dbus_socket_printable (socket_transport->fd));
  
  if (transport->connection == NULL)
    return;

  if (transport->disconnected)
    {
      _dbus_assert (socket_transport->read_watch == NULL);
      return;
    }
  
  _dbus_transport_ref (transport);

  if (_dbus_transport_try_to_authenticate (transport))
    need_read_watch =
      (_dbus_counter_get_size_value (transport->live_messages) < transport->max_live_messages_size) &&
      (_dbus_counter_get_unix_fd_value (transport->live_messages) < transport->max_live_messages_unix_fds);
  else
    {
      if (transport->receive_credentials_pending)
        need_read_watch = TRUE;
      else
        {
          /* The reason to disable need_read_watch when not WAITING_FOR_INPUT
           * is to avoid spinning on the file descriptor when we're waiting
           * to write or for some other part of the auth process
           */
          DBusAuthState auth_state;
          
          auth_state = _dbus_auth_do_work (transport->auth);

          /* If we need memory we install the read watch just in case,
           * if there's no need for it, it will get de-installed
           * next time we try reading. If we're authenticated we
           * install it since we normally have it installed while
           * authenticated.
           */
          if (auth_state == DBUS_AUTH_STATE_WAITING_FOR_INPUT ||
              auth_state == DBUS_AUTH_STATE_WAITING_FOR_MEMORY ||
              auth_state == DBUS_AUTH_STATE_AUTHENTICATED)
            need_read_watch = TRUE;
          else
            need_read_watch = FALSE;
        }
    }

  _dbus_verbose ("  setting read watch enabled = %d\n", need_read_watch);
  _dbus_connection_toggle_watch_unlocked (transport->connection,
                                          socket_transport->read_watch,
                                          need_read_watch);

  _dbus_transport_unref (transport);
}
static void
check_write_watch (DBusTransport *transport)
{
  DBusTransportSocket *socket_transport = (DBusTransportSocket*) transport;
  dbus_bool_t needed;

  if (transport->connection == NULL)
    return;

  if (transport->disconnected)
    {
      _dbus_assert (socket_transport->write_watch == NULL);
      return;
    }
  
  _dbus_transport_ref (transport);

  if (_dbus_transport_try_to_authenticate (transport))
    needed = _dbus_connection_has_messages_to_send_unlocked (transport->connection);
  else
    {
      if (transport->send_credentials_pending)
        needed = TRUE;
      else
        {
          DBusAuthState auth_state;
          
          auth_state = _dbus_auth_do_work (transport->auth);
          
          /* If we need memory we install the write watch just in case,
           * if there's no need for it, it will get de-installed
           * next time we try reading.
           */
          if (auth_state == DBUS_AUTH_STATE_HAVE_BYTES_TO_SEND ||
              auth_state == DBUS_AUTH_STATE_WAITING_FOR_MEMORY)
            needed = TRUE;
          else
            needed = FALSE;
        }
    }

  _dbus_verbose ("check_write_watch(): needed = %d on connection %p watch %p fd = %" DBUS_SOCKET_FORMAT " outgoing messages exist %d\n",
                 needed, transport->connection, socket_transport->write_watch,
                 _dbus_socket_printable (socket_transport->fd),
                 _dbus_connection_has_messages_to_send_unlocked (transport->connection));

  _dbus_connection_toggle_watch_unlocked (transport->connection,
                                          socket_transport->write_watch,
                                          needed);

  _dbus_transport_unref (transport);
}
示例#3
0
/**
 * sends the nonce over a given socket. Blocks while doing so.
 *
 * @param fd the file descriptor to write the nonce data to (usually a socket)
 * @param noncefile the noncefile location to read the nonce from
 * @param error contains error details if FALSE is returned
 * @return TRUE iff the nonce was successfully sent. Note that this does not
 * indicate whether the server accepted the nonce.
 */
dbus_bool_t
_dbus_send_nonce (DBusSocket        fd,
                  const DBusString *noncefile,
                  DBusError        *error)
{
  dbus_bool_t read_result;
  int send_result;
  DBusString nonce;

  _DBUS_ASSERT_ERROR_IS_CLEAR (error);

  if (_dbus_string_get_length (noncefile) == 0)
    return FALSE;

  if (!_dbus_string_init (&nonce))
    {
      dbus_set_error (error, DBUS_ERROR_NO_MEMORY, NULL);
      return FALSE;
    }

  read_result = _dbus_read_nonce (noncefile, &nonce, error);
  if (!read_result)
    {
      _DBUS_ASSERT_ERROR_IS_SET (error);
      _dbus_string_free (&nonce);
      return FALSE;
    }
  _DBUS_ASSERT_ERROR_IS_CLEAR (error);

  send_result = _dbus_write_socket (fd, &nonce, 0, _dbus_string_get_length (&nonce));

  _dbus_string_free (&nonce);

  if (send_result == -1)
    {
      dbus_set_error (error,
                      _dbus_error_from_system_errno (),
                      "Failed to send nonce (fd=%" DBUS_SOCKET_FORMAT "): %s",
                      _dbus_socket_printable (fd),
                      _dbus_strerror_from_errno ());
      return FALSE;
    }

  return TRUE;
}
/* returns false on out-of-memory */
static dbus_bool_t
do_reading (DBusTransport *transport)
{
  DBusTransportSocket *socket_transport = (DBusTransportSocket*) transport;
  DBusString *buffer;
  int bytes_read;
  int total;
  dbus_bool_t oom;
  int saved_errno;

  _dbus_verbose ("fd = %" DBUS_SOCKET_FORMAT "\n",
                 _dbus_socket_printable (socket_transport->fd));
  
  /* No messages without authentication! */
  if (!_dbus_transport_try_to_authenticate (transport))
    return TRUE;

  oom = FALSE;
  
  total = 0;

 again:
  
  /* See if we've exceeded max messages and need to disable reading */
  check_read_watch (transport);
  
  if (total > socket_transport->max_bytes_read_per_iteration)
    {
      _dbus_verbose ("%d bytes exceeds %d bytes read per iteration, returning\n",
                     total, socket_transport->max_bytes_read_per_iteration);
      goto out;
    }

  _dbus_assert (socket_transport->read_watch != NULL ||
                transport->disconnected);
  
  if (transport->disconnected)
    goto out;

  if (!dbus_watch_get_enabled (socket_transport->read_watch))
    return TRUE;
  
  if (_dbus_auth_needs_decoding (transport->auth))
    {
      /* Does fd passing even make sense with encoded data? */
      _dbus_assert(!DBUS_TRANSPORT_CAN_SEND_UNIX_FD(transport));

      if (_dbus_string_get_length (&socket_transport->encoded_incoming) > 0)
        bytes_read = _dbus_string_get_length (&socket_transport->encoded_incoming);
      else
        bytes_read = _dbus_read_socket (socket_transport->fd,
                                        &socket_transport->encoded_incoming,
                                        socket_transport->max_bytes_read_per_iteration);

      saved_errno = _dbus_save_socket_errno ();

      _dbus_assert (_dbus_string_get_length (&socket_transport->encoded_incoming) ==
                    bytes_read);
      
      if (bytes_read > 0)
        {
          _dbus_message_loader_get_buffer (transport->loader,
                                           &buffer);

          if (!_dbus_auth_decode_data (transport->auth,
                                       &socket_transport->encoded_incoming,
                                       buffer))
            {
              _dbus_verbose ("Out of memory decoding incoming data\n");
              _dbus_message_loader_return_buffer (transport->loader,
                                              buffer);

              oom = TRUE;
              goto out;
            }

          _dbus_message_loader_return_buffer (transport->loader,
                                              buffer);

          _dbus_string_set_length (&socket_transport->encoded_incoming, 0);
          _dbus_string_compact (&socket_transport->encoded_incoming, 2048);
        }
    }
  else
    {
      _dbus_message_loader_get_buffer (transport->loader,
                                       &buffer);

#ifdef HAVE_UNIX_FD_PASSING
      if (DBUS_TRANSPORT_CAN_SEND_UNIX_FD(transport))
        {
          int *fds;
          unsigned int n_fds;

          if (!_dbus_message_loader_get_unix_fds(transport->loader, &fds, &n_fds))
            {
              _dbus_verbose ("Out of memory reading file descriptors\n");
              _dbus_message_loader_return_buffer (transport->loader, buffer);
              oom = TRUE;
              goto out;
            }

          bytes_read = _dbus_read_socket_with_unix_fds(socket_transport->fd,
                                                       buffer,
                                                       socket_transport->max_bytes_read_per_iteration,
                                                       fds, &n_fds);
          saved_errno = _dbus_save_socket_errno ();

          if (bytes_read >= 0 && n_fds > 0)
            _dbus_verbose("Read %i unix fds\n", n_fds);

          _dbus_message_loader_return_unix_fds(transport->loader, fds, bytes_read < 0 ? 0 : n_fds);
        }
      else
#endif
        {
          bytes_read = _dbus_read_socket (socket_transport->fd,
                                          buffer, socket_transport->max_bytes_read_per_iteration);
          saved_errno = _dbus_save_socket_errno ();
        }

      _dbus_message_loader_return_buffer (transport->loader,
                                          buffer);
    }

  if (bytes_read < 0)
    {
      /* EINTR already handled for us */

      if (_dbus_get_is_errno_enomem (saved_errno))
        {
          _dbus_verbose ("Out of memory in read()/do_reading()\n");
          oom = TRUE;
          goto out;
        }
      else if (_dbus_get_is_errno_eagain_or_ewouldblock (saved_errno))
        goto out;
      else
        {
          _dbus_verbose ("Error reading from remote app: %s\n",
                         _dbus_strerror (saved_errno));
          do_io_error (transport);
          goto out;
        }
    }
  else if (bytes_read == 0)
    {
      _dbus_verbose ("Disconnected from remote app\n");
      do_io_error (transport);
      goto out;
    }
  else
    {
      _dbus_verbose (" read %d bytes\n", bytes_read);
      
      total += bytes_read;      

      if (!_dbus_transport_queue_messages (transport))
        {
          oom = TRUE;
          _dbus_verbose (" out of memory when queueing messages we just read in the transport\n");
          goto out;
        }
      
      /* Try reading more data until we get EAGAIN and return, or
       * exceed max bytes per iteration.  If in blocking mode of
       * course we'll block instead of returning.
       */
      goto again;
    }

 out:
  if (oom)
    return FALSE;
  else
    return TRUE;
}
/* returns false on oom */
static dbus_bool_t
do_writing (DBusTransport *transport)
{
  int total;
  DBusTransportSocket *socket_transport = (DBusTransportSocket*) transport;
  dbus_bool_t oom;
  
  /* No messages without authentication! */
  if (!_dbus_transport_try_to_authenticate (transport))
    {
      _dbus_verbose ("Not authenticated, not writing anything\n");
      return TRUE;
    }

  if (transport->disconnected)
    {
      _dbus_verbose ("Not connected, not writing anything\n");
      return TRUE;
    }

#if 1
  _dbus_verbose ("do_writing(), have_messages = %d, fd = %" DBUS_SOCKET_FORMAT "\n",
                 _dbus_connection_has_messages_to_send_unlocked (transport->connection),
                 _dbus_socket_printable (socket_transport->fd));
#endif
  
  oom = FALSE;
  total = 0;

  while (!transport->disconnected &&
         _dbus_connection_has_messages_to_send_unlocked (transport->connection))
    {
      int bytes_written;
      DBusMessage *message;
      const DBusString *header;
      const DBusString *body;
      int header_len, body_len;
      int total_bytes_to_write;
      int saved_errno;
      
      if (total > socket_transport->max_bytes_written_per_iteration)
        {
          _dbus_verbose ("%d bytes exceeds %d bytes written per iteration, returning\n",
                         total, socket_transport->max_bytes_written_per_iteration);
          goto out;
        }
      
      message = _dbus_connection_get_message_to_send (transport->connection);
      _dbus_assert (message != NULL);
      dbus_message_lock (message);

#if 0
      _dbus_verbose ("writing message %p\n", message);
#endif
      
      _dbus_message_get_network_data (message,
                                      &header, &body);

      header_len = _dbus_string_get_length (header);
      body_len = _dbus_string_get_length (body);

      if (_dbus_auth_needs_encoding (transport->auth))
        {
          /* Does fd passing even make sense with encoded data? */
          _dbus_assert(!DBUS_TRANSPORT_CAN_SEND_UNIX_FD(transport));

          if (_dbus_string_get_length (&socket_transport->encoded_outgoing) == 0)
            {
              if (!_dbus_auth_encode_data (transport->auth,
                                           header, &socket_transport->encoded_outgoing))
                {
                  oom = TRUE;
                  goto out;
                }
              
              if (!_dbus_auth_encode_data (transport->auth,
                                           body, &socket_transport->encoded_outgoing))
                {
                  _dbus_string_set_length (&socket_transport->encoded_outgoing, 0);
                  oom = TRUE;
                  goto out;
                }
            }
          
          total_bytes_to_write = _dbus_string_get_length (&socket_transport->encoded_outgoing);

#if 0
          _dbus_verbose ("encoded message is %d bytes\n",
                         total_bytes_to_write);
#endif
          
          bytes_written =
            _dbus_write_socket (socket_transport->fd,
                                &socket_transport->encoded_outgoing,
                                socket_transport->message_bytes_written,
                                total_bytes_to_write - socket_transport->message_bytes_written);
          saved_errno = _dbus_save_socket_errno ();
        }
      else
        {
          total_bytes_to_write = header_len + body_len;

#if 0
          _dbus_verbose ("message is %d bytes\n",
                         total_bytes_to_write);
#endif

#ifdef HAVE_UNIX_FD_PASSING
          if (socket_transport->message_bytes_written <= 0 && DBUS_TRANSPORT_CAN_SEND_UNIX_FD(transport))
            {
              /* Send the fds along with the first byte of the message */
              const int *unix_fds;
              unsigned n;

              _dbus_message_get_unix_fds(message, &unix_fds, &n);

              bytes_written =
                _dbus_write_socket_with_unix_fds_two (socket_transport->fd,
                                                      header,
                                                      socket_transport->message_bytes_written,
                                                      header_len - socket_transport->message_bytes_written,
                                                      body,
                                                      0, body_len,
                                                      unix_fds,
                                                      n);
              saved_errno = _dbus_save_socket_errno ();

              if (bytes_written > 0 && n > 0)
                _dbus_verbose("Wrote %i unix fds\n", n);
            }
          else
#endif
            {
              if (socket_transport->message_bytes_written < header_len)
                {
                  bytes_written =
                    _dbus_write_socket_two (socket_transport->fd,
                                            header,
                                            socket_transport->message_bytes_written,
                                            header_len - socket_transport->message_bytes_written,
                                            body,
                                            0, body_len);
                }
              else
                {
                  bytes_written =
                    _dbus_write_socket (socket_transport->fd,
                                        body,
                                        (socket_transport->message_bytes_written - header_len),
                                        body_len -
                                        (socket_transport->message_bytes_written - header_len));
                }

              saved_errno = _dbus_save_socket_errno ();
            }
        }

      if (bytes_written < 0)
        {
          /* EINTR already handled for us */
          
          /* If the other end closed the socket with close() or shutdown(), we
           * receive EPIPE here but we must not close the socket yet: there
           * might still be some data to read. See:
           * http://lists.freedesktop.org/archives/dbus/2008-March/009526.html
           */
          
          if (_dbus_get_is_errno_eagain_or_ewouldblock (saved_errno) || _dbus_get_is_errno_epipe (saved_errno))
            goto out;

          /* Since Linux commit 25888e (from 2.6.37-rc4, Nov 2010), sendmsg()
           * on Unix sockets returns -1 errno=ETOOMANYREFS when the passfd
           * mechanism (SCM_RIGHTS) is used recursively with a recursion level
           * of maximum 4. The kernel does not have an API to check whether
           * the passed fds can be forwarded and it can change asynchronously.
           * See:
           * https://bugs.freedesktop.org/show_bug.cgi?id=80163
           */

          else if (_dbus_get_is_errno_etoomanyrefs (saved_errno))
            {
              /* We only send fds in the first byte of the message.
               * ETOOMANYREFS cannot happen after.
               */
              _dbus_assert (socket_transport->message_bytes_written == 0);

              _dbus_verbose (" discard message of %d bytes due to ETOOMANYREFS\n",
                             total_bytes_to_write);

              socket_transport->message_bytes_written = 0;
              _dbus_string_set_length (&socket_transport->encoded_outgoing, 0);
              _dbus_string_compact (&socket_transport->encoded_outgoing, 2048);

              /* The message was not actually sent but it needs to be removed
               * from the outgoing queue
               */
              _dbus_connection_message_sent_unlocked (transport->connection,
                                                      message);
            }
          else
            {
              _dbus_verbose ("Error writing to remote app: %s\n",
                             _dbus_strerror (saved_errno));
              do_io_error (transport);
              goto out;
            }
        }
      else
        {
          _dbus_verbose (" wrote %d bytes of %d\n", bytes_written,
                         total_bytes_to_write);
          
          total += bytes_written;
          socket_transport->message_bytes_written += bytes_written;

          _dbus_assert (socket_transport->message_bytes_written <=
                        total_bytes_to_write);
          
          if (socket_transport->message_bytes_written == total_bytes_to_write)
            {
              socket_transport->message_bytes_written = 0;
              _dbus_string_set_length (&socket_transport->encoded_outgoing, 0);
              _dbus_string_compact (&socket_transport->encoded_outgoing, 2048);

              _dbus_connection_message_sent_unlocked (transport->connection,
                                                      message);
            }
        }
    }

 out:
  if (oom)
    return FALSE;
  else
    return TRUE;
}
/**
 * @todo We need to have a way to wake up the select sleep if
 * a new iteration request comes in with a flag (read/write) that
 * we're not currently serving. Otherwise a call that just reads
 * could block a write call forever (if there are no incoming
 * messages).
 */
static  void
socket_do_iteration (DBusTransport *transport,
                   unsigned int   flags,
                   int            timeout_milliseconds)
{
  DBusTransportSocket *socket_transport = (DBusTransportSocket*) transport;
  DBusPollFD poll_fd;
  int poll_res;
  int poll_timeout;

  _dbus_verbose (" iteration flags = %s%s timeout = %d read_watch = %p write_watch = %p fd = %" DBUS_SOCKET_FORMAT "\n",
                 flags & DBUS_ITERATION_DO_READING ? "read" : "",
                 flags & DBUS_ITERATION_DO_WRITING ? "write" : "",
                 timeout_milliseconds,
                 socket_transport->read_watch,
                 socket_transport->write_watch,
                 _dbus_socket_printable (socket_transport->fd));
  
  /* the passed in DO_READING/DO_WRITING flags indicate whether to
   * read/write messages, but regardless of those we may need to block
   * for reading/writing to do auth.  But if we do reading for auth,
   * we don't want to read any messages yet if not given DO_READING.
   */

  poll_fd.fd = _dbus_socket_get_pollable (socket_transport->fd);
  poll_fd.events = 0;
  
  if (_dbus_transport_try_to_authenticate (transport))
    {
      /* This is kind of a hack; if we have stuff to write, then try
       * to avoid the poll. This is probably about a 5% speedup on an
       * echo client/server.
       *
       * If both reading and writing were requested, we want to avoid this
       * since it could have funky effects:
       *   - both ends spinning waiting for the other one to read
       *     data so they can finish writing
       *   - prioritizing all writing ahead of reading
       */
      if ((flags & DBUS_ITERATION_DO_WRITING) &&
          !(flags & (DBUS_ITERATION_DO_READING | DBUS_ITERATION_BLOCK)) &&
          !transport->disconnected &&
          _dbus_connection_has_messages_to_send_unlocked (transport->connection))
        {
          do_writing (transport);

          if (transport->disconnected ||
              !_dbus_connection_has_messages_to_send_unlocked (transport->connection))
            goto out;
        }

      /* If we get here, we decided to do the poll() after all */
      _dbus_assert (socket_transport->read_watch);
      if (flags & DBUS_ITERATION_DO_READING)
	poll_fd.events |= _DBUS_POLLIN;

      _dbus_assert (socket_transport->write_watch);
      if (flags & DBUS_ITERATION_DO_WRITING)
        poll_fd.events |= _DBUS_POLLOUT;
    }
  else
    {
      DBusAuthState auth_state;
      
      auth_state = _dbus_auth_do_work (transport->auth);

      if (transport->receive_credentials_pending ||
          auth_state == DBUS_AUTH_STATE_WAITING_FOR_INPUT)
	poll_fd.events |= _DBUS_POLLIN;

      if (transport->send_credentials_pending ||
          auth_state == DBUS_AUTH_STATE_HAVE_BYTES_TO_SEND)
	poll_fd.events |= _DBUS_POLLOUT;
    }

  if (poll_fd.events)
    {
      int saved_errno;

      if (flags & DBUS_ITERATION_BLOCK)
	poll_timeout = timeout_milliseconds;
      else
	poll_timeout = 0;

      /* For blocking selects we drop the connection lock here
       * to avoid blocking out connection access during a potentially
       * indefinite blocking call. The io path is still protected
       * by the io_path_cond condvar, so we won't reenter this.
       */
      if (flags & DBUS_ITERATION_BLOCK)
        {
          _dbus_verbose ("unlock pre poll\n");
          _dbus_connection_unlock (transport->connection);
        }
      
    again:
      poll_res = _dbus_poll (&poll_fd, 1, poll_timeout);
      saved_errno = _dbus_save_socket_errno ();

      if (poll_res < 0 && _dbus_get_is_errno_eintr (saved_errno))
	goto again;

      if (flags & DBUS_ITERATION_BLOCK)
        {
          _dbus_verbose ("lock post poll\n");
          _dbus_connection_lock (transport->connection);
        }
      
      if (poll_res >= 0)
        {
          if (poll_res == 0)
            poll_fd.revents = 0; /* some concern that posix does not guarantee this;
                                  * valgrind flags it as an error. though it probably
                                  * is guaranteed on linux at least.
                                  */
          
          if (poll_fd.revents & _DBUS_POLLERR)
            do_io_error (transport);
          else
            {
              dbus_bool_t need_read = (poll_fd.revents & _DBUS_POLLIN) > 0;
              dbus_bool_t need_write = (poll_fd.revents & _DBUS_POLLOUT) > 0;
	      dbus_bool_t authentication_completed;

              _dbus_verbose ("in iteration, need_read=%d need_write=%d\n",
                             need_read, need_write);
              do_authentication (transport, need_read, need_write,
				 &authentication_completed);

	      /* See comment in socket_handle_watch. */
	      if (authentication_completed)
                goto out;
                                 
              if (need_read && (flags & DBUS_ITERATION_DO_READING))
                do_reading (transport);
              if (need_write && (flags & DBUS_ITERATION_DO_WRITING))
                do_writing (transport);
            }
        }
      else
        {
          _dbus_verbose ("Error from _dbus_poll(): %s\n",
                         _dbus_strerror (saved_errno));
        }
    }


 out:
  /* We need to install the write watch only if we did not
   * successfully write everything. Note we need to be careful that we
   * don't call check_write_watch *before* do_writing, since it's
   * inefficient to add the write watch, and we can avoid it most of
   * the time since we can write immediately.
   * 
   * However, we MUST always call check_write_watch(); DBusConnection code
   * relies on the fact that running an iteration will notice that
   * messages are pending.
   */
  check_write_watch (transport);

  _dbus_verbose (" ... leaving do_iteration()\n");
}
示例#7
0
static dbus_bool_t
do_check_nonce (DBusSocket fd, const DBusString *nonce, DBusError *error)
{
  DBusString buffer;
  DBusString p;
  size_t nleft;
  dbus_bool_t result;
  int n;

  _DBUS_ASSERT_ERROR_IS_CLEAR (error);

  nleft = 16;

  /* This is a trick to make it safe to call _dbus_string_free on these
   * strings during error unwinding, even if allocating memory for them
   * fails. A constant DBusString is considered to be valid to "free",
   * even though there is nothing to free (of course the free operation
   * is trivial, because it does not own its own buffer); but
   * unlike a mutable DBusString, initializing a constant DBusString
   * cannot fail.
   *
   * We must successfully re-initialize the strings to be mutable before
   * writing to them, of course.
   */
  _dbus_string_init_const (&buffer, "");
  _dbus_string_init_const (&p, "");

  if (   !_dbus_string_init (&buffer)
      || !_dbus_string_init (&p) ) {
        dbus_set_error (error, DBUS_ERROR_NO_MEMORY, NULL);
        _dbus_string_free (&p);
        _dbus_string_free (&buffer);
        return FALSE;
      }

  while (nleft)
    {
      int saved_errno;

      n = _dbus_read_socket (fd, &p, nleft);
      saved_errno = _dbus_save_socket_errno ();

      if (n == -1 && _dbus_get_is_errno_eintr (saved_errno))
        ;
      else if (n == -1 && _dbus_get_is_errno_eagain_or_ewouldblock (saved_errno))
        _dbus_sleep_milliseconds (100);
      else if (n==-1)
        {
          dbus_set_error (error, DBUS_ERROR_IO_ERROR, "Could not read nonce from socket (fd=%" DBUS_SOCKET_FORMAT ")", _dbus_socket_printable (fd));
          _dbus_string_free (&p);
          _dbus_string_free (&buffer);
          return FALSE;
        }
      else if (!n)
        {
          _dbus_string_free (&p);
          _dbus_string_free (&buffer);
          dbus_set_error (error, DBUS_ERROR_IO_ERROR, "Could not read nonce from socket (fd=%" DBUS_SOCKET_FORMAT ")", _dbus_socket_printable (fd));
          return FALSE;
        }
      else
        {
          if (!_dbus_string_append_len (&buffer, _dbus_string_get_const_data (&p), n))
            {
              dbus_set_error (error, DBUS_ERROR_NO_MEMORY, NULL);
              _dbus_string_free (&p);
              _dbus_string_free (&buffer);
              return FALSE;
            }
          nleft -= n;
        }
    }

  result =  _dbus_string_equal_len (&buffer, nonce, 16);
  if (!result)
    dbus_set_error (error, DBUS_ERROR_ACCESS_DENIED, "Nonces do not match, access denied (fd=%" DBUS_SOCKET_FORMAT ")", _dbus_socket_printable (fd));

  _dbus_string_free (&p);
  _dbus_string_free (&buffer);

  return result;
}