ares_process.c

/* $Id$ */

/* Copyright 1998 by the Massachusetts Institute of Technology.
 * Copyright (C) 2004-2008 by Daniel Stenberg
 *
 * Permission to use, copy, modify, and distribute this
 * software and its documentation for any purpose and without
 * fee is hereby granted, provided that the above copyright
 * notice appear in all copies and that both that copyright
 * notice and this permission notice appear in supporting
 * documentation, and that the name of M.I.T. not be used in
 * advertising or publicity pertaining to distribution of the
 * software without specific, written prior permission.
 * M.I.T. makes no representations about the suitability of
 * this software for any purpose.  It is provided "as is"
 * without express or implied warranty.
 */

#include "setup.h"

#if defined(WIN32) && !defined(WATT32)
#include "nameser.h"

#else
#ifdef HAVE_SYS_SOCKET_H
#include <sys/socket.h>
#endif
#ifdef HAVE_SYS_UIO_H
#include <sys/uio.h>
#endif
#ifdef HAVE_NETINET_IN_H
#include <netinet/in.h> /* <netinet/tcp.h> may need it */
#endif
#ifdef HAVE_NETINET_TCP_H
#include <netinet/tcp.h> /* for TCP_NODELAY */
#endif
#ifdef HAVE_NETDB_H
#include <netdb.h>
#endif
#ifdef HAVE_ARPA_NAMESER_H
#include <arpa/nameser.h>
#endif
#ifdef HAVE_ARPA_NAMESER_COMPAT_H
#include <arpa/nameser_compat.h>
#endif
#ifdef HAVE_SYS_TIME_H
#include <sys/time.h>
#endif
#endif /* WIN32 && !WATT32 */

#ifdef HAVE_STRINGS_H
#include <strings.h>
#endif
#ifdef HAVE_UNISTD_H
#include <unistd.h>
#endif
#ifdef HAVE_SYS_IOCTL_H
#include <sys/ioctl.h>
#endif
#ifdef NETWARE
#include <sys/filio.h>
#endif

#include <assert.h>
#include <string.h>
#include <stdlib.h>
#include <fcntl.h>
#include <time.h>
#include <errno.h>

#include "ares.h"
#include "ares_dns.h"
#include "ares_private.h"


static int try_again(int errnum);
static void write_tcp_data(ares_channel channel, fd_set *write_fds,
                           ares_socket_t write_fd, struct timeval *now);
static void read_tcp_data(ares_channel channel, fd_set *read_fds,
                          ares_socket_t read_fd, struct timeval *now);
static void read_udp_packets(ares_channel channel, fd_set *read_fds,
                             ares_socket_t read_fd, struct timeval *now);
static void advance_tcp_send_queue(ares_channel channel, int whichserver,
                                   ssize_t num_bytes);
static void process_timeouts(ares_channel channel, struct timeval *now);
static void process_broken_connections(ares_channel channel,
                                       struct timeval *now);
static void process_answer(ares_channel channel, unsigned char *abuf,
                           int alen, int whichserver, int tcp,
                           struct timeval *now);
static void handle_error(ares_channel channel, int whichserver,
                         struct timeval *now);
static void skip_server(ares_channel channel, struct query *query,
                        int whichserver);
static void next_server(ares_channel channel, struct query *query,
                        struct timeval *now);
static int configure_socket(int s, ares_channel channel);
static int open_tcp_socket(ares_channel channel, struct server_state *server);
static int open_udp_socket(ares_channel channel, struct server_state *server);
static int same_questions(const unsigned char *qbuf, int qlen,
                          const unsigned char *abuf, int alen);
static void end_query(ares_channel channel, struct query *query, int status,
                      unsigned char *abuf, int alen);

/* return true if now is exactly check time or later */
int ares__timedout(struct timeval *now,
                   struct timeval *check)
{
  int secs = (now->tv_sec - check->tv_sec);

  if(secs > 0)
    return 1; /* yes, timed out */
  if(secs < 0)
    return 0; /* nope, not timed out */

  /* if the full seconds were identical, check the sub second parts */
  return (now->tv_usec - check->tv_usec >= 0);
}

/* add the specific number of milliseconds to the time in the first argument */
int ares__timeadd(struct timeval *now,
                  int millisecs)
{
  now->tv_sec += millisecs/1000;
  now->tv_usec += (millisecs%1000)*1000;

  if(now->tv_usec >= 1000000) {
    ++(now->tv_sec);
    now->tv_usec -= 1000000;
  }

  return 0;
}

/* return time offset between now and (future) check, in milliseconds */
int ares__timeoffset(struct timeval *now,
                     struct timeval *check)
{
  int secs = (check->tv_sec - now->tv_sec); /* this many seconds */
  int us = (check->tv_usec - now->tv_usec); /* this many microseconds */

  return secs*1000 + us/1000; /* return them combined as milliseconds */
}


/* Something interesting happened on the wire, or there was a timeout.
 * See what's up and respond accordingly.
 */
void ares_process(ares_channel channel, fd_set *read_fds, fd_set *write_fds)
{
  struct timeval now = ares__tvnow();

  write_tcp_data(channel, write_fds, ARES_SOCKET_BAD, &now);
  read_tcp_data(channel, read_fds, ARES_SOCKET_BAD, &now);
  read_udp_packets(channel, read_fds, ARES_SOCKET_BAD, &now);
  process_timeouts(channel, &now);
  process_broken_connections(channel, &now);
}

/* Something interesting happened on the wire, or there was a timeout.
 * See what's up and respond accordingly.
 */
void ares_process_fd(ares_channel channel,
                     ares_socket_t read_fd, /* use ARES_SOCKET_BAD or valid
                                               file descriptors */
                     ares_socket_t write_fd)
{
  struct timeval now = ares__tvnow();

  write_tcp_data(channel, NULL, write_fd, &now);
  read_tcp_data(channel, NULL, read_fd, &now);
  read_udp_packets(channel, NULL, read_fd, &now);
  process_timeouts(channel, &now);
}


/* Return 1 if the specified error number describes a readiness error, or 0
 * otherwise. This is mostly for HP-UX, which could return EAGAIN or
 * EWOULDBLOCK. See this man page
 *
 *      http://devrsrc1.external.hp.com/STKS/cgi-bin/man2html?manpage=/usr/share/man/man2.Z/send.2
 */
static int try_again(int errnum)
{
#if !defined EWOULDBLOCK && !defined EAGAIN
#error "Neither EWOULDBLOCK nor EAGAIN defined"
#endif
  switch (errnum)
    {
#ifdef EWOULDBLOCK
    case EWOULDBLOCK:
      return 1;
#endif
#if defined EAGAIN && EAGAIN != EWOULDBLOCK
    case EAGAIN:
      return 1;
#endif
    }
  return 0;
}