ares_process.c

/* $Id$ */

/* Copyright 1998 by the Massachusetts Institute of Technology.
 *
 * 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
#include <sys/socket.h>
#ifdef HAVE_SYS_UIO_H
#include <sys/uio.h>
#endif
#include <netinet/tcp.h>   /* for TCP_NODELAY */
#include <netinet/in.h>
#include <netdb.h>
#include <arpa/nameser.h>
#ifdef HAVE_ARPA_NAMESER_COMPAT_H
#include <arpa/nameser_compat.h>
#endif
#endif /* WIN32 && !WATT32 */

#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 <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, time_t now);
static void read_tcp_data(ares_channel channel, fd_set *read_fds,
                          ares_socket_t read_fd, time_t now);
static void read_udp_packets(ares_channel channel, fd_set *read_fds,
                             ares_socket_t read_fd, time_t now);
static void process_timeouts(ares_channel channel, time_t now);
static void process_broken_connections(ares_channel channel, time_t now);
static void process_answer(ares_channel channel, unsigned char *abuf,
                           int alen, int whichserver, int tcp, time_t now);
static void handle_error(ares_channel channel, int whichserver, time_t now);
static void skip_server(ares_channel channel, struct query *query,
                        int whichserver);
static struct query *next_server(ares_channel channel, struct query *query, time_t now);
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 struct query *end_query(ares_channel channel, struct query *query, int status,
                      unsigned char *abuf, int alen);

/* 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)
{
  time_t now;

  time(&now);
  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)
{
  time_t now;

  time(&now);
  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;
}

/* If any TCP sockets select true for writing, write out queued data
 * we have for them.
 */
static void write_tcp_data(ares_channel channel,
                           fd_set *write_fds,
                           ares_socket_t write_fd,
                           time_t now)
{
  struct server_state *server;
  struct send_request *sendreq;
  struct iovec *vec;
  int i;
  ssize_t scount;
  ssize_t wcount;
  size_t n;

  if(!write_fds && (write_fd == ARES_SOCKET_BAD))
    /* no possible action */
    return;

  for (i = 0; i < channel->nservers; i++)
    {
      /* Make sure server has data to send and is selected in write_fds or
         write_fd. */
      server = &channel->servers[i];
      if (!server->qhead || server->tcp_socket == ARES_SOCKET_BAD || server->is_broken)
        continue;

      if(write_fds) {
        if(!FD_ISSET(server->tcp_socket, write_fds))
          continue;
      }
      else {
        if(server->tcp_socket != write_fd)
          continue;
      }

      if(write_fds)
        /* If there's an error and we close this socket, then open
         * another with the same fd to talk to another server, then we
         * don't want to think that it was the new socket that was
         * ready. This is not disastrous, but is likely to result in
         * extra system calls and confusion. */
        FD_CLR(server->tcp_socket, write_fds);

      /* Count the number of send queue items. */
      n = 0;
      for (sendreq = server->qhead; sendreq; sendreq = sendreq->next)
        n++;

      /* Allocate iovecs so we can send all our data at once. */
      vec = malloc(n * sizeof(struct iovec));
      if (vec)
        {
          /* Fill in the iovecs and send. */
          n = 0;
          for (sendreq = server->qhead; sendreq; sendreq = sendreq->next)
            {
              vec[n].iov_base = (char *) sendreq->data;
              vec[n].iov_len = sendreq->len;
              n++;
            }
          wcount = (ssize_t)writev(server->tcp_socket, vec, (int)n);