dbus-transport-socket.c

/* -*- mode: C; c-file-style: "gnu"; indent-tabs-mode: nil; -*- */
/* dbus-transport-socket.c  Socket subclasses of DBusTransport
 *
 * Copyright (C) 2002, 2003, 2004, 2006  Red Hat Inc.
 *
 * Licensed under the Academic Free License version 2.1
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 2 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software
 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301  USA
 *
 */
 
#include <config.h>
#include "dbus-internals.h"
#include "dbus-connection-internal.h"
#include "dbus-nonce.h"
#include "dbus-transport-socket.h"
#include "dbus-transport-protected.h"
#include "dbus-watch.h"
#include "dbus-credentials.h"
 
typedef struct DBusTransportSocket DBusTransportSocket;
 
struct DBusTransportSocket
{
  DBusTransport base;                   
  DBusSocket fd;                        
  DBusWatch *read_watch;                
  DBusWatch *write_watch;               
  int max_bytes_read_per_iteration;     
  int max_bytes_written_per_iteration;  
  int message_bytes_written;            
  DBusString encoded_outgoing;          
  DBusString encoded_incoming;          
};
 
static void
free_watches (DBusTransport *transport)
{
  DBusTransportSocket *socket_transport = (DBusTransportSocket*) transport;
 
  _dbus_verbose ("start\n");
  
  if (socket_transport->read_watch)
    {
      if (transport->connection)
        _dbus_connection_remove_watch_unlocked (transport->connection,
                                                socket_transport->read_watch);
      _dbus_watch_invalidate (socket_transport->read_watch);
      _dbus_watch_unref (socket_transport->read_watch);
      socket_transport->read_watch = NULL;
    }
 
  if (socket_transport->write_watch)
    {
      if (transport->connection)
        _dbus_connection_remove_watch_unlocked (transport->connection,
                                                socket_transport->write_watch);
      _dbus_watch_invalidate (socket_transport->write_watch);
      _dbus_watch_unref (socket_transport->write_watch);
      socket_transport->write_watch = NULL;
    }
 
  _dbus_verbose ("end\n");
}
 
static void
socket_finalize (DBusTransport *transport)
{
  DBusTransportSocket *socket_transport = (DBusTransportSocket*) transport;
 
  _dbus_verbose ("\n");
  
  free_watches (transport);
 
  _dbus_string_free (&socket_transport->encoded_outgoing);
  _dbus_string_free (&socket_transport->encoded_incoming);
  
  _dbus_transport_finalize_base (transport);
 
  _dbus_assert (socket_transport->read_watch == NULL);
  _dbus_assert (socket_transport->write_watch == NULL);
  
  dbus_free (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);
}
 
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
do_io_error (DBusTransport *transport)
{
  _dbus_transport_ref (transport);
  _dbus_transport_disconnect (transport);
  _dbus_transport_unref (transport);
}
 
/* return value is whether we successfully read any new data. */
static dbus_bool_t
read_data_into_auth (DBusTransport *transport,
                     dbus_bool_t   *oom)
{
  DBusTransportSocket *socket_transport = (DBusTransportSocket*) transport;
  DBusString *buffer;
  int bytes_read;
  int saved_errno;
 
  *oom = FALSE;
 
  _dbus_auth_get_buffer (transport->auth, &buffer);
  
  bytes_read = _dbus_read_socket (socket_transport->fd,
                                  buffer, socket_transport->max_bytes_read_per_iteration);
  saved_errno = _dbus_save_socket_errno ();
 
  _dbus_auth_return_buffer (transport->auth, buffer);
 
  if (bytes_read > 0)
    {
      _dbus_verbose (" read %d bytes in auth phase\n", bytes_read);
 
      return TRUE;
    }
  else if (bytes_read < 0)
    {
      /* EINTR already handled for us */
 
      if (_dbus_get_is_errno_enomem (saved_errno))
        {
          *oom = TRUE;
        }
      else if (_dbus_get_is_errno_eagain_or_ewouldblock (saved_errno))
        ; /* do nothing, just return FALSE below */
      else
        {
          _dbus_verbose ("Error reading from remote app: %s\n",
                         _dbus_strerror (saved_errno));
          do_io_error (transport);
        }
 
      return FALSE;
    }
  else
    {
      _dbus_assert (bytes_read == 0);
      
      _dbus_verbose ("Disconnected from remote app\n");
      do_io_error (transport);
 
      return FALSE;
    }
}
 
/* Return value is whether we successfully wrote any bytes */
static dbus_bool_t
write_data_from_auth (DBusTransport *transport)
{
  DBusTransportSocket *socket_transport = (DBusTransportSocket*) transport;
  int bytes_written;
  int saved_errno;
  const DBusString *buffer;
 
  if (!_dbus_auth_get_bytes_to_send (transport->auth,
                                     &buffer))
    return FALSE;
  
  bytes_written = _dbus_write_socket (socket_transport->fd,
                                      buffer,
                                      0, _dbus_string_get_length (buffer));
  saved_errno = _dbus_save_socket_errno ();
 
  if (bytes_written > 0)
    {
      _dbus_auth_bytes_sent (transport->auth, bytes_written);
      return TRUE;
    }
  else if (bytes_written < 0)
    {
      /* EINTR already handled for us */
      
      if (_dbus_get_is_errno_eagain_or_ewouldblock (saved_errno))
        ;
      else
        {
          _dbus_verbose ("Error writing to remote app: %s\n",
                         _dbus_strerror (saved_errno));
          do_io_error (transport);
        }
    }
 
  return FALSE;
}
 
/* FALSE on OOM */
static dbus_bool_t
exchange_credentials (DBusTransport *transport,
                      dbus_bool_t    do_reading,
                      dbus_bool_t    do_writing)
{
  DBusTransportSocket *socket_transport = (DBusTransportSocket*) transport;
  DBusError error = DBUS_ERROR_INIT;
 
  _dbus_verbose ("exchange_credentials: do_reading = %d, do_writing = %d\n",
                  do_reading, do_writing);
 
  if (do_writing && transport->send_credentials_pending)
    {
      if (_dbus_send_credentials_socket (socket_transport->fd,
                                         &error))
        {
          transport->send_credentials_pending = FALSE;
        }
      else
        {
          _dbus_verbose ("Failed to write credentials: %s\n", error.message);
          dbus_error_free (&error);
          do_io_error (transport);
        }
    }
  
  if (do_reading && transport->receive_credentials_pending)
    {
      /* FIXME this can fail due to IO error _or_ OOM, broken
       * (somewhat tricky to fix since the OOM error can be set after
       * we already read the credentials byte, so basically we need to
       * separate reading the byte and storing it in the
       * transport->credentials). Does not really matter for now
       * because storing in credentials never actually fails on unix.
       */      
      if (_dbus_read_credentials_socket (socket_transport->fd,
                                         transport->credentials,
                                         &error))
        {
          transport->receive_credentials_pending = FALSE;
        }
      else
        {
          _dbus_verbose ("Failed to read credentials %s\n", error.message);
          dbus_error_free (&error);
          do_io_error (transport);
        }
    }
 
  if (!(transport->send_credentials_pending ||
        transport->receive_credentials_pending))
    {
      if (!_dbus_auth_set_credentials (transport->auth,
                                       transport->credentials))
        return FALSE;
    }
 
  return TRUE;
}
 
static dbus_bool_t
do_authentication (DBusTransport *transport,
                   dbus_bool_t    do_reading,
                   dbus_bool_t    do_writing,
                   dbus_bool_t   *auth_completed)
{
  dbus_bool_t oom;
  dbus_bool_t orig_auth_state;
 
  oom = FALSE;
  
  orig_auth_state = _dbus_transport_try_to_authenticate (transport);
 
  /* This is essential to avoid the check_write_watch() at the end,
   * we don't want to add a write watch in do_iteration before
   * we try writing and get EAGAIN
   */
  if (orig_auth_state)
    {
      if (auth_completed)
        *auth_completed = FALSE;
      return TRUE;
    }
  
  _dbus_transport_ref (transport);
  
  while (!_dbus_transport_try_to_authenticate (transport) &&
         _dbus_transport_get_is_connected (transport))
    {      
      if (!exchange_credentials (transport, do_reading, do_writing))
        {
          /* OOM */
          oom = TRUE;
          goto out;
        }
      
      if (transport->send_credentials_pending ||
          transport->receive_credentials_pending)
        {
          _dbus_verbose ("send_credentials_pending = %d receive_credentials_pending = %d\n",
                         transport->send_credentials_pending,
                         transport->receive_credentials_pending);
          goto out;
        }
 
#define TRANSPORT_SIDE(t) ((t)->is_server ? "server" : "client")
      switch (_dbus_auth_do_work (transport->auth))
        {
        case DBUS_AUTH_STATE_WAITING_FOR_INPUT:
          _dbus_verbose (" %s auth state: waiting for input\n",
                         TRANSPORT_SIDE (transport));
          if (!do_reading || !read_data_into_auth (transport, &oom))
            goto out;
          break;
      
        case DBUS_AUTH_STATE_WAITING_FOR_MEMORY:
          _dbus_verbose (" %s auth state: waiting for memory\n",
                         TRANSPORT_SIDE (transport));
          oom = TRUE;
          goto out;
          break;
      
        case DBUS_AUTH_STATE_HAVE_BYTES_TO_SEND:
          _dbus_verbose (" %s auth state: bytes to send\n",
                         TRANSPORT_SIDE (transport));
          if (!do_writing || !write_data_from_auth (transport))
            goto out;
          break;
      
        case DBUS_AUTH_STATE_NEED_DISCONNECT:
          _dbus_verbose (" %s auth state: need to disconnect\n",
                         TRANSPORT_SIDE (transport));
          do_io_error (transport);
          break;
      
        case DBUS_AUTH_STATE_AUTHENTICATED:
          _dbus_verbose (" %s auth state: authenticated\n",
                         TRANSPORT_SIDE (transport));
          break;
 
        case DBUS_AUTH_STATE_INVALID:
          /* fall through */
        default:
          _dbus_assert_not_reached ("invalid auth state");
        }
    }
 
 out:
  if (auth_completed)
    *auth_completed = (orig_auth_state != _dbus_transport_try_to_authenticate (transport));
  
  check_read_watch (transport);
  check_write_watch (transport);
  _dbus_transport_unref (transport);
 
  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;
}
 
/* 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,
                                           NULL,
                                           NULL);
 
          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
    {
      int max_to_read = DBUS_MAXIMUM_MESSAGE_LENGTH;
      dbus_bool_t may_read_unix_fds = TRUE;
 
      _dbus_message_loader_get_buffer (transport->loader,
                                       &buffer,
                                       &max_to_read,
                                       &may_read_unix_fds);
 
      if (max_to_read > socket_transport->max_bytes_read_per_iteration)
        max_to_read = socket_transport->max_bytes_read_per_iteration;
 
#ifdef HAVE_UNIX_FD_PASSING
      if (DBUS_TRANSPORT_CAN_SEND_UNIX_FD(transport) && may_read_unix_fds)
        {
          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,
                                                       max_to_read,
                                                       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, max_to_read);
          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;
}
 
static dbus_bool_t
unix_error_with_read_to_come (DBusTransport *itransport,
                              DBusWatch     *watch,
                              unsigned int   flags)
{
  DBusTransportSocket *transport = (DBusTransportSocket *) itransport;
 
  if (!(flags & DBUS_WATCH_HANGUP || flags & DBUS_WATCH_ERROR))
    return FALSE;
   
  /* If we have a read watch enabled ...
     we -might have data incoming ... => handle the HANGUP there */
  if (watch != transport->read_watch &&
      _dbus_watch_get_enabled (transport->read_watch))
    return FALSE;
      
  return TRUE; 
}
 
static dbus_bool_t
socket_handle_watch (DBusTransport *transport,
                   DBusWatch     *watch,
                   unsigned int   flags)
{
  DBusTransportSocket *socket_transport = (DBusTransportSocket*) transport;
 
  _dbus_assert (watch == socket_transport->read_watch ||
                watch == socket_transport->write_watch);
  _dbus_assert (watch != NULL);
  
  /* If we hit an error here on a write watch, don't disconnect the transport yet because data can
   * still be in the buffer and do_reading may need several iteration to read
   * it all (because of its max_bytes_read_per_iteration limit). 
   */
  if (!(flags & DBUS_WATCH_READABLE) && unix_error_with_read_to_come (transport, watch, flags))
    {
      _dbus_verbose ("Hang up or error on watch\n");
      _dbus_transport_disconnect (transport);
      return TRUE;
    }
  
  if (watch == socket_transport->read_watch &&
      (flags & DBUS_WATCH_READABLE))
    {
      dbus_bool_t auth_finished;
#if 1
      _dbus_verbose ("handling read watch %p flags = %x\n",
                     watch, flags);
#endif
      if (!do_authentication (transport, TRUE, FALSE, &auth_finished))
        return FALSE;
 
      /* We don't want to do a read immediately following
       * a successful authentication.  This is so we
       * have a chance to propagate the authentication
       * state further up.  Specifically, we need to
       * process any pending data from the auth object.
       */
      if (!auth_finished)
        {
          if (!do_reading (transport))
            {
              _dbus_verbose ("no memory to read\n");
              return FALSE;
            }
        }
      else
        {
          _dbus_verbose ("Not reading anything since we just completed the authentication\n");
        }
    }
  else if (watch == socket_transport->write_watch &&
           (flags & DBUS_WATCH_WRITABLE))
    {
#if 1
      _dbus_verbose ("handling write watch, have_outgoing_messages = %d\n",
                     _dbus_connection_has_messages_to_send_unlocked (transport->connection));
#endif
      if (!do_authentication (transport, FALSE, TRUE, NULL))
        return FALSE;
      
      if (!do_writing (transport))
        {
          _dbus_verbose ("no memory to write\n");
          return FALSE;
        }
 
      /* See if we still need the write watch */
      check_write_watch (transport);
    }
#ifdef DBUS_ENABLE_VERBOSE_MODE
  else
    {
      if (watch == socket_transport->read_watch)
        _dbus_verbose ("asked to handle read watch with non-read condition 0x%x\n",
                       flags);
      else if (watch == socket_transport->write_watch)
        _dbus_verbose ("asked to handle write watch with non-write condition 0x%x\n",
                       flags);
      else
        _dbus_verbose ("asked to handle watch %p on fd %" DBUS_SOCKET_FORMAT " that we don't recognize\n",
                       watch, _dbus_socket_printable (_dbus_watch_get_socket (watch)));
    }
#endif /* DBUS_ENABLE_VERBOSE_MODE */
 
  return TRUE;
}
 
static void
socket_disconnect (DBusTransport *transport)
{
  DBusTransportSocket *socket_transport = (DBusTransportSocket*) transport;
 
  _dbus_verbose ("\n");
  
  free_watches (transport);
  
  _dbus_close_socket (socket_transport->fd, NULL);
  _dbus_socket_invalidate (&socket_transport->fd);
}
 
static dbus_bool_t
socket_connection_set (DBusTransport *transport)
{
  DBusTransportSocket *socket_transport = (DBusTransportSocket*) transport;
 
  _dbus_watch_set_handler (socket_transport->write_watch,
                           _dbus_connection_handle_watch,
                           transport->connection, NULL);
 
  _dbus_watch_set_handler (socket_transport->read_watch,
                           _dbus_connection_handle_watch,
                           transport->connection, NULL);
  
  if (!_dbus_connection_add_watch_unlocked (transport->connection,
                                            socket_transport->write_watch))
    return FALSE;
 
  if (!_dbus_connection_add_watch_unlocked (transport->connection,
                                            socket_transport->read_watch))
    {
      _dbus_connection_remove_watch_unlocked (transport->connection,
                                              socket_transport->write_watch);
      return FALSE;
    }
 
  check_read_watch (transport);
  check_write_watch (transport);
 
  return TRUE;
}
 
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");
}
 
static void
socket_live_messages_changed (DBusTransport *transport)
{
  /* See if we should look for incoming messages again */
  check_read_watch (transport);
}
 
 
static dbus_bool_t
socket_get_socket_fd (DBusTransport *transport,
                      DBusSocket    *fd_p)
{
  DBusTransportSocket *socket_transport = (DBusTransportSocket*) transport;
  
  *fd_p = socket_transport->fd;
  
  return TRUE;
}
 
static const DBusTransportVTable socket_vtable = {
  socket_finalize,
  socket_handle_watch,
  socket_disconnect,
  socket_connection_set,
  socket_do_iteration,
  socket_live_messages_changed,
  socket_get_socket_fd
};
 
DBusTransport*
_dbus_transport_new_for_socket (DBusSocket        fd,
                                const DBusString *server_guid,
                                const DBusString *address)
{
  DBusTransportSocket *socket_transport;
  DBusString invalid = _DBUS_STRING_INIT_INVALID;
 
  socket_transport = dbus_new0 (DBusTransportSocket, 1);
  if (socket_transport == NULL)
    return NULL;
 
  /* So they can be "freed" without error */
  socket_transport->encoded_outgoing = invalid;
  socket_transport->encoded_incoming = invalid;
 
  if (!_dbus_string_init (&socket_transport->encoded_outgoing))
    goto failed;
 
  if (!_dbus_string_init (&socket_transport->encoded_incoming))
    goto failed;
  
  socket_transport->write_watch = _dbus_watch_new (_dbus_socket_get_pollable (fd),
                                                 DBUS_WATCH_WRITABLE,
                                                 FALSE,
                                                 NULL, NULL, NULL);
  if (socket_transport->write_watch == NULL)
    goto failed;
  
  socket_transport->read_watch = _dbus_watch_new (_dbus_socket_get_pollable (fd),
                                                DBUS_WATCH_READABLE,
                                                FALSE,
                                                NULL, NULL, NULL);
  if (socket_transport->read_watch == NULL)
    goto failed;
 
  if (!_dbus_transport_init_base (&socket_transport->base,
                                  &socket_vtable,
                                  server_guid, address))
    goto failed;
 
#ifdef HAVE_UNIX_FD_PASSING
  _dbus_auth_set_unix_fd_possible(socket_transport->base.auth, _dbus_socket_can_pass_unix_fd(fd));
#endif
 
  socket_transport->fd = fd;
  socket_transport->message_bytes_written = 0;
  
  /* These values should probably be tunable or something. */     
  socket_transport->max_bytes_read_per_iteration = 2048;
  socket_transport->max_bytes_written_per_iteration = 2048;
  
  return (DBusTransport*) socket_transport;
 
failed:
  if (socket_transport->read_watch != NULL)
    {
      _dbus_watch_invalidate (socket_transport->read_watch);
      _dbus_watch_unref (socket_transport->read_watch);
    }
 
  if (socket_transport->write_watch != NULL)
    {
      _dbus_watch_invalidate (socket_transport->write_watch);
      _dbus_watch_unref (socket_transport->write_watch);
    }
 
  _dbus_string_free (&socket_transport->encoded_incoming);
  _dbus_string_free (&socket_transport->encoded_outgoing);
  dbus_free (socket_transport);
  return NULL;
}
 
DBusTransport*
_dbus_transport_new_for_tcp_socket (const char     *host,
                                    const char     *port,
                                    const char     *family,
                                    const char     *noncefile,
                                    DBusError      *error)
{
  DBusSocket fd;
  DBusTransport *transport;
  DBusString address;
  
  _DBUS_ASSERT_ERROR_IS_CLEAR (error);
 
  if (!_dbus_string_init (&address))
    {
      dbus_set_error (error, DBUS_ERROR_NO_MEMORY, NULL);
      return NULL;
    }
 
  if (host == NULL)
    host = "localhost";
 
  if (!_dbus_string_append (&address, noncefile ? "nonce-tcp:" : "tcp:"))
    goto error;
 
  if (!_dbus_string_append (&address, "host=") ||
      !_dbus_string_append (&address, host))
    goto error;
 
  if (!_dbus_string_append (&address, ",port=") ||
      !_dbus_string_append (&address, port))
    goto error;
 
  if (family != NULL &&
      (!_dbus_string_append (&address, ",family=") ||
       !_dbus_string_append (&address, family)))
    goto error;
 
  if (noncefile != NULL &&
      (!_dbus_string_append (&address, ",noncefile=") ||
       !_dbus_string_append (&address, noncefile)))
    goto error;
 
  fd = _dbus_connect_tcp_socket_with_nonce (host, port, family, noncefile, error);
  if (!_dbus_socket_is_valid (fd))
    {
      _DBUS_ASSERT_ERROR_IS_SET (error);
      _dbus_string_free (&address);
      return NULL;
    }
 
  _dbus_verbose ("Successfully connected to tcp socket %s:%s\n",
                 host, port);
  
  transport = _dbus_transport_new_for_socket (fd, NULL, &address);
  _dbus_string_free (&address);
  if (transport == NULL)
    {
      dbus_set_error (error, DBUS_ERROR_NO_MEMORY, NULL);
      _dbus_close_socket (fd, NULL);
      _dbus_socket_invalidate (&fd);
    }
 
  return transport;
 
error:
  _dbus_string_free (&address);
  dbus_set_error (error, DBUS_ERROR_NO_MEMORY, NULL);
  return NULL;
}
 
DBusTransportOpenResult
_dbus_transport_open_socket(DBusAddressEntry  *entry,
                            DBusTransport    **transport_p,                            
                            DBusError         *error)
{
  const char *method;
  dbus_bool_t isTcp;
  dbus_bool_t isNonceTcp;
  
  method = dbus_address_entry_get_method (entry);
  _dbus_assert (method != NULL);
 
  isTcp = strcmp (method, "tcp") == 0;
  isNonceTcp = strcmp (method, "nonce-tcp") == 0;
 
  if (isTcp || isNonceTcp)
    {
      const char *host = dbus_address_entry_get_value (entry, "host");
      const char *port = dbus_address_entry_get_value (entry, "port");
      const char *family = dbus_address_entry_get_value (entry, "family");
      const char *noncefile = dbus_address_entry_get_value (entry, "noncefile");
 
      if ((isNonceTcp == TRUE) != (noncefile != NULL)) {
          _dbus_set_bad_address (error, method, "noncefile", NULL);
          return DBUS_TRANSPORT_OPEN_BAD_ADDRESS;
      }
 
      if (port == NULL)
        {
          _dbus_set_bad_address (error, method, "port", NULL);
          return DBUS_TRANSPORT_OPEN_BAD_ADDRESS;
        }
 
      *transport_p = _dbus_transport_new_for_tcp_socket (host, port, family, noncefile, error);
      if (*transport_p == NULL)
        {
          _DBUS_ASSERT_ERROR_IS_SET (error);
          return DBUS_TRANSPORT_OPEN_DID_NOT_CONNECT;
        }
      else
        {
          _DBUS_ASSERT_ERROR_IS_CLEAR (error);
          return DBUS_TRANSPORT_OPEN_OK;
        }
    }
  else
    {
      _DBUS_ASSERT_ERROR_IS_CLEAR (error);
      return DBUS_TRANSPORT_OPEN_NOT_HANDLED;
    }
}