path: root/src/host.c

/* Host name resolution and matching.
   Copyright (C) 1996-2012, 2015, 2018-2023 Free Software Foundation,
   Inc.

This file is part of GNU Wget.

GNU Wget 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 3 of the License, or
 (at your option) any later version.

GNU Wget 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 Wget.  If not, see <http://www.gnu.org/licenses/>.

Additional permission under GNU GPL version 3 section 7

If you modify this program, or any covered work, by linking or
combining it with the OpenSSL project's OpenSSL library (or a
modified version of that library), containing parts covered by the
terms of the OpenSSL or SSLeay licenses, the Free Software Foundation
grants you additional permission to convey the resulting work.
Corresponding Source for a non-source form of such a combination
shall include the source code for the parts of OpenSSL used as well
as that of the covered work.  */

#include "wget.h"

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <assert.h>

#ifndef WINDOWS
# include <sys/types.h>
# include <sys/socket.h>
# include <netinet/in.h>
# ifndef __BEOS__
#  include <arpa/inet.h>
# endif
# ifdef __VMS
#  include "vms_ip.h"
# else /* def __VMS */
#  include <netdb.h>
# endif /* def __VMS [else] */
# define SET_H_ERRNO(err) ((void)(h_errno = (err)))
#else  /* WINDOWS */
# include <winsock2.h>
# include <ws2tcpip.h>
# define SET_H_ERRNO(err) WSASetLastError (err)
#endif /* WINDOWS */

#include <errno.h>

#include "utils.h"
#include "host.h"
#include "url.h"
#include "hash.h"
#include "ptimer.h"

#ifndef NO_ADDRESS
# define NO_ADDRESS NO_DATA
#endif

#if !HAVE_DECL_H_ERRNO && !defined(WINDOWS)
extern int h_errno;
#endif


/* Lists of IP addresses that result from running DNS queries.  See
   lookup_host for details.  */

struct address_list {
  int count;                    /* number of addresses */
  ip_address *addresses;        /* pointer to the string of addresses */

  int faulty;                   /* number of addresses known not to work. */
  bool connected;               /* whether we were able to connect to
                                   one of the addresses in the list,
                                   at least once. */

  int refcount;                 /* reference count; when it drops to
                                   0, the entry is freed. */
};

/* Get the bounds of the address list.  */

void
address_list_get_bounds (const struct address_list *al, int *start, int *end)
{
  *start = al->faulty;
  *end   = al->count;
}

/* Return a pointer to the address at position POS.  */

const ip_address *
address_list_address_at (const struct address_list *al, int pos)
{
  assert (pos >= al->faulty && pos < al->count);
  return al->addresses + pos;
}

/* Return true if AL contains IP, false otherwise.  */

bool
address_list_contains (const struct address_list *al, const ip_address *ip)
{
  int i;
  switch (ip->family)
    {
    case AF_INET:
      for (i = 0; i < al->count; i++)
        {
          ip_address *cur = al->addresses + i;
          if (cur->family == AF_INET
              && (cur->data.d4.s_addr == ip->data.d4.s_addr))
            return true;
        }
      return false;
#ifdef ENABLE_IPV6
    case AF_INET6:
      for (i = 0; i < al->count; i++)
        {
          ip_address *cur = al->addresses + i;
          if (cur->family == AF_INET6
#ifdef HAVE_SOCKADDR_IN6_SCOPE_ID
              && cur->ipv6_scope == ip->ipv6_scope
#endif
              && IN6_ARE_ADDR_EQUAL (&cur->data.d6, &ip->data.d6))
            return true;
        }
      return false;
#endif /* ENABLE_IPV6 */
    default:
      abort ();
    }
}

/* Mark the INDEXth element of AL as faulty, so that the next time
   this address list is used, the faulty element will be skipped.  */

void
address_list_set_faulty (struct address_list *al, int index)
{
  /* We assume that the address list is traversed in order, so that a
     "faulty" attempt is always preceded with all-faulty addresses,
     and this is how Wget uses it.  */
  assert (index == al->faulty);
  if (index != al->faulty)
    {
      logprintf (LOG_ALWAYS, "index: %d\nal->faulty: %d\n", index, al->faulty);
      logprintf (LOG_ALWAYS, _("Error in handling the address list.\n"));
      logprintf (LOG_ALWAYS, _("Please report this issue to bug-wget@gnu.org\n"));
      abort();
    }

  ++al->faulty;
  if (al->faulty >= al->count)
    /* All addresses have been proven faulty.  Since there's not much
       sense in returning the user an empty address list the next
       time, we'll rather make them all clean, so that they can be
       retried anew.  */
    al->faulty = 0;
}

/* Set the "connected" flag to true.  This flag used by connect.c to
   see if the host perhaps needs to be resolved again.  */

void
address_list_set_connected (struct address_list *al)
{
  al->connected = true;
}

/* Return the value of the "connected" flag. */

bool
address_list_connected_p (const struct address_list *al)
{
  return al->connected;
}

#ifdef ENABLE_IPV6

/* Create an address_list from the addresses in the given struct
   addrinfo.  */

static struct address_list *
address_list_from_addrinfo (const struct addrinfo *ai)
{
  struct address_list *al;
  const struct addrinfo *ptr;
  int cnt;
  ip_address *ip;

  cnt = 0;
  for (ptr = ai; ptr != NULL ; ptr = ptr->ai_next)
    if (ptr->ai_family == AF_INET || ptr->ai_family == AF_INET6)
      ++cnt;
  if (cnt == 0)
    return NULL;

  al = xnew0 (struct address_list);
  al->addresses = xnew_array (ip_address, cnt);
  al->count     = cnt;
  al->refcount  = 1;

  ip = al->addresses;
  for (ptr = ai; ptr != NULL; ptr = ptr->ai_next)
    if (ptr->ai_family == AF_INET6)
      {
        const struct sockaddr_in6 *sin6 =
          (const struct sockaddr_in6 *)ptr->ai_addr;
        ip->family = AF_INET6;
        ip->data.d6 = sin6->sin6_addr;
#ifdef HAVE_SOCKADDR_IN6_SCOPE_ID
        ip->ipv6_scope = sin6->sin6_scope_id;
#endif
        ++ip;
      }
    else if (ptr->ai_family == AF_INET)
      {
        const struct sockaddr_in *sin =
          (const struct sockaddr_in *)ptr->ai_addr;
        ip->family = AF_INET;
        ip->data.d4 = sin->sin_addr;
        ++ip;
      }
  assert (ip - al->addresses == cnt);
  return al;
}

#define IS_IPV4(addr) (((const ip_address *) addr)->family == AF_INET)

/* Compare two IP addresses by family, giving preference to the IPv4
   address (sorting it first).  In other words, return -1 if ADDR1 is
   IPv4 and ADDR2 is IPv6, +1 if ADDR1 is IPv6 and ADDR2 is IPv4, and
   0 otherwise.

   This is intended to be used as the comparator arg to a qsort-like
   sorting function, which is why it accepts generic pointers.  */

static int
cmp_prefer_ipv4 (const void *addr1, const void *addr2)
{
  return !IS_IPV4 (addr1) - !IS_IPV4 (addr2);
}

#define IS_IPV6(addr) (((const ip_address *) addr)->family == AF_INET6)

/* Like the above, but give preference to the IPv6 address.  */

static int
cmp_prefer_ipv6 (const void *addr1, const void *addr2)
{
  return !IS_IPV6 (addr1) - !IS_IPV6 (addr2);
}

#else  /* not ENABLE_IPV6 */

/* Create an address_list from a NULL-terminated vector of IPv4
   addresses.  This kind of vector is returned by gethostbyname.  */

static struct address_list *
address_list_from_ipv4_addresses (char **vec)
{
  int count, i;
  struct address_list *al = xnew0 (struct address_list);

  count = 0;
  while (vec[count])
    ++count;
  assert (count > 0);

  al->addresses = xnew_array (ip_address, count);
  al->count     = count;
  al->refcount  = 1;

  for (i = 0; i < count; i++)
    {
      ip_address *ip = &al->addresses[i];
      ip->family = AF_INET;
      memcpy (IP_INADDR_DATA (ip), vec[i], 4);
    }

  return al;
}

#endif /* not ENABLE_IPV6 */

static void
address_list_delete (struct address_list *al)
{
  xfree (al->addresses);
  xfree (al);
}

/* Mark the address list as being no longer in use.  This will reduce
   its reference count which will cause the list to be freed when the
   count reaches 0.  */

void
address_list_release (struct address_list *al)
{
  --al->refcount;
  DEBUGP (("Releasing 0x%0*lx (new refcount %d).\n", PTR_FORMAT (al),
           al->refcount));
  if (al->refcount <= 0)
    {
      DEBUGP (("Deleting unused 0x%0*lx.\n", PTR_FORMAT (al)));
      address_list_delete (al);
    }
}

/* Versions of gethostbyname and getaddrinfo that support timeout. */

#ifndef ENABLE_IPV6

struct ghbnwt_context {
  const char *host_name;
  struct hostent *hptr;
};

static void
gethostbyname_with_timeout_callback (void *arg)
{
  struct ghbnwt_context *ctx = (struct ghbnwt_context *)arg;
  ctx->hptr = gethostbyname (ctx->host_name);
}

/* Just like gethostbyname, except it times out after TIMEOUT seconds.
   In case of timeout, NULL is returned and errno is set to ETIMEDOUT.
   The function makes sure that when NULL is returned for reasons
   other than timeout, errno is reset.  */

static struct hostent *
gethostbyname_with_timeout (const char *host_name, double timeout)
{
  struct ghbnwt_context ctx;
  ctx.host_name = host_name;
  if (run_with_timeout (timeout, gethostbyname_with_timeout_callback, &ctx))
    {
      SET_H_ERRNO (HOST_NOT_FOUND);
      errno = ETIMEDOUT;
      return NULL;
    }
  if (!ctx.hptr)
    errno = 0;
  return ctx.hptr;
}

/* Print error messages for host errors.  */
static const char *
host_errstr (int error)
{
  /* Can't use switch since some of these constants can be equal,
     which makes the compiler complain about duplicate case
     values.  */
  if (error == HOST_NOT_FOUND
      || error == NO_RECOVERY
      || error == NO_DATA
      || error == NO_ADDRESS)
    return _("Unknown host");
  else if (error == TRY_AGAIN)
    /* Message modeled after what gai_strerror returns in similar
       circumstances.  */
    return _("Temporary failure in name resolution");
  else
    return _("Unknown error");
}

#else  /* ENABLE_IPV6 */

struct gaiwt_context {
  const char *node;
  const char *service;
  const struct addrinfo *hints;
  struct addrinfo **res;
  int exit_code;
};

static void
getaddrinfo_with_timeout_callback (void *arg)
{
  struct gaiwt_context *ctx = (struct gaiwt_context *)arg;
  ctx->exit_code = getaddrinfo (ctx->node, ctx->service, ctx->hints, ctx->res);
}

/* Just like getaddrinfo, except it times out after TIMEOUT seconds.
   In case of timeout, the EAI_SYSTEM error code is returned and errno
   is set to ETIMEDOUT.  */

static int
getaddrinfo_with_timeout (const char *node, const char *service,
                          const struct addrinfo *hints, struct addrinfo **res,
                          double timeout)
{
  struct gaiwt_context ctx;
  ctx.node = node;
  ctx.service = service;
  ctx.hints = hints;
  ctx.res = res;

  if (run_with_timeout (timeout, getaddrinfo_with_timeout_callback, &ctx))
    {
      errno = ETIMEDOUT;
      return EAI_SYSTEM;
    }
  return ctx.exit_code;
}

#endif /* ENABLE_IPV6 */

/* Return a textual representation of ADDR, i.e. the dotted quad for
   IPv4 addresses, and the colon-separated list of hex words (with all
   zeros omitted, etc.) for IPv6 addresses.  */

const char *
print_address (const ip_address *addr)
{
  static char buf[64];

  if (!inet_ntop (addr->family, IP_INADDR_DATA (addr), buf, sizeof buf))
    snprintf (buf, sizeof buf, "<error: %s>", strerror (errno));

  return buf;
}

/* The following two functions were adapted from glibc's
   implementation of inet_pton, written by Paul Vixie. */

static bool
is_valid_ipv4_address (const char *str, const char *end)
{
  bool saw_digit = false;
  int octets = 0;
  int val = 0;

  while (str < end)
    {
      int ch = *str++;

      if (ch >= '0' && ch <= '9')
        {
          val = val * 10 + (ch - '0');

          if (val > 255)
            return false;
          if (!saw_digit)
            {
              if (++octets > 4)
                return false;
              saw_digit = true;
            }
        }
      else if (ch == '.' && saw_digit)
        {
          if (octets == 4)
            return false;
          val = 0;
          saw_digit = false;
        }
      else
        return false;
    }
  if (octets < 4)
    return false;

  return true;
}

bool
is_valid_ipv6_address (const char *str, const char *end)
{
  /* Use lower-case for these to avoid clash with system headers.  */
  enum {
    ns_inaddrsz  = 4,
    ns_in6addrsz = 16,
    ns_int16sz   = 2
  };

  const char *curtok;
  int tp;
  const char *colonp;
  bool saw_xdigit;
  unsigned int val;

  tp = 0;
  colonp = NULL;

  if (str == end)
    return false;

  /* Leading :: requires some special handling. */
  if (*str == ':')
    {
      ++str;
      if (str == end || *str != ':')
        return false;
    }

  curtok = str;
  saw_xdigit = false;
  val = 0;

  while (str < end)
    {
      int ch = *str++;

      /* if ch is a number, add it to val. */
      if (c_isxdigit (ch))
        {
          val <<= 4;
          val |= _unhex (ch);
          if (val > 0xffff)
            return false;
          saw_xdigit = true;
          continue;
        }

      /* if ch is a colon ... */
      if (ch == ':')
        {
          curtok = str;
          if (!saw_xdigit)
            {
              if (colonp != NULL)
                return false;
              colonp = str + tp;
              continue;
            }
          else if (str == end)
            return false;
          if (tp > ns_in6addrsz - ns_int16sz)
            return false;
          tp += ns_int16sz;
          saw_xdigit = false;
          val = 0;
          continue;
        }

      /* if ch is a dot ... */
      if (ch == '.' && (tp <= ns_in6addrsz - ns_inaddrsz)
          && is_valid_ipv4_address (curtok, end) == 1)
        {
          tp += ns_inaddrsz;
          saw_xdigit = false;
          break;
        }

      return false;
    }

  if (saw_xdigit)
    {
      if (tp > ns_in6addrsz - ns_int16sz)
        return false;
      tp += ns_int16sz;
    }

  if (colonp != NULL)
    {
      if (tp == ns_in6addrsz)
        return false;
      tp = ns_in6addrsz;
    }

  if (tp != ns_in6addrsz)
    return false;

  return true;
}

/* Simple host cache, used by lookup_host to speed up resolving.  The
   cache doesn't handle TTL because Wget is a fairly short-lived
   application.  Refreshing is attempted when connect fails, though --
   see connect_to_host.  */

/* Mapping between known hosts and to lists of their addresses. */
static struct hash_table *host_name_addresses_map;


/* Return the host's resolved addresses from the cache, if
   available.  */

static struct address_list *
cache_query (const char *host)
{
  struct address_list *al;
  if (!host_name_addresses_map)
    return NULL;
  al = hash_table_get (host_name_addresses_map, host);
  if (al)
    {
      DEBUGP (("Found %s in host_name_addresses_map (%p)\n", host, (void *) al));
      ++al->refcount;
      return al;
    }
  return NULL;
}

/* Cache the DNS lookup of HOST.  Subsequent invocations of
   lookup_host will return the cached value.  */

static void
cache_store (const char *host, struct address_list *al)
{
  if (!host_name_addresses_map)
    host_name_addresses_map = make_nocase_string_hash_table (0);

  ++al->refcount;
  hash_table_put (host_name_addresses_map, xstrdup_lower (host), al);

  IF_DEBUG
    {
      int i;
      debug_logprintf ("Caching %s =>", host);
      for (i = 0; i < al->count; i++)
        debug_logprintf (" %s", print_address (al->addresses + i));
      debug_logprintf ("\n");
    }
}

/* Remove HOST from the DNS cache.  Does nothing is HOST is not in
   the cache.  */

static void
cache_remove (const char *host)
{
  struct address_list *al;
  if (!host_name_addresses_map)
    return;
  al = hash_table_get (host_name_addresses_map, host);
  if (al)
    {
      address_list_release (al);
      hash_table_remove (host_name_addresses_map, host);
    }
}

#ifdef HAVE_LIBCARES
#include <sys/select.h>
#include <ares.h>
extern ares_channel ares;

static struct address_list *
merge_address_lists (struct address_list *al1, struct address_list *al2)
{
  int count = al1->count + al2->count;

  /* merge al2 into al1 */
  al1->addresses = xrealloc (al1->addresses, sizeof (ip_address) * count);
  memcpy (al1->addresses + al1->count, al2->addresses, sizeof (ip_address) * al2->count);
  al1->count = count;

  address_list_delete (al2);

  return al1;
}

static struct address_list *
address_list_from_hostent (struct hostent *host)
{
  int count, i;
  struct address_list *al = xnew0 (struct address_list);

  for (count = 0; host->h_addr_list[count]; count++)
    ;

  assert (count > 0);

  al->addresses = xnew_array (ip_address, count);
  al->count     = count;
  al->refcount  = 1;

  for (i = 0; i < count; i++)
    {
      ip_address *ip = &al->addresses[i];
      ip->family = host->h_addrtype;
      memcpy (IP_INADDR_DATA (ip), host->h_addr_list[i], ip->family == AF_INET ? 4 : 16);
    }

  return al;
}

/* Since GnuLib's select() (i.e. rpl_select()) cannot handle socket-numbers
 * returned from C-ares, we must use the original select() from Winsock.
 */
#ifdef WINDOWS
#undef select
#endif

static void
wait_ares (ares_channel channel)
{
  struct ptimer *timer = NULL;

  if (opt.dns_timeout)
    timer = ptimer_new ();

  for (;;)
    {
      struct timeval *tvp, tv;
      fd_set read_fds, write_fds;
      int nfds, rc;

      FD_ZERO (&read_fds);
      FD_ZERO (&write_fds);
      nfds = ares_fds (channel, &read_fds, &write_fds);
      if (nfds == 0)
        break;

      if (timer)
        {
          double max = opt.dns_timeout - ptimer_measure (timer);

          tv.tv_sec = (long) max;
          tv.tv_usec = 1000000 * (max - (long) max);
          tvp = ares_timeout (channel, &tv, &tv);
        }
      else
        tvp = ares_timeout (channel, NULL, &tv);

      rc = select (nfds, &read_fds, &write_fds, NULL, tvp);
      if (rc == 0 && timer && ptimer_measure (timer) >= opt.dns_timeout)
        ares_cancel (channel);
      else
        ares_process (channel, &read_fds, &write_fds);
    }
  if (timer)
    ptimer_destroy (timer);
}

static void
callback (void *arg, int status, int timeouts _GL_UNUSED, struct hostent *host)
{
  struct address_list **al = (struct address_list **) arg;

  if (!host || status != ARES_SUCCESS)
    {
      *al = NULL;
      return;
    }

  *al = address_list_from_hostent (host);
}
#endif

/* Look up HOST in DNS and return a list of IP addresses.

   This function caches its result so that, if the same host is passed
   the second time, the addresses are returned without DNS lookup.
   (Use LH_REFRESH to force lookup, or set opt.dns_cache to 0 to
   globally disable caching.)

   The order of the returned addresses is affected by the setting of
   opt.prefer_family: if it is set to prefer_ipv4, IPv4 addresses are
   placed at the beginning; if it is prefer_ipv6, IPv6 ones are placed
   at the beginning; otherwise, the order is left intact.  The
   relative order of addresses with the same family is left
   undisturbed in either case.

   FLAGS can be a combination of:
     LH_SILENT  - don't print the "resolving ... done" messages.
     LH_BIND    - resolve addresses for use with bind, which under
                  IPv6 means to use AI_PASSIVE flag to getaddrinfo.
                  Passive lookups are not cached under IPv6.
     LH_REFRESH - if HOST is cached, remove the entry from the cache
                  and resolve it anew.  */

struct address_list *
lookup_host (const char *host, int flags)
{
  struct address_list *al;
  bool silent = !!(flags & LH_SILENT);
  bool use_cache;
  bool numeric_address = false;
  double timeout = opt.dns_timeout;

#ifndef ENABLE_IPV6
  /* If we're not using getaddrinfo, first check if HOST specifies a
     numeric IPv4 address.  Some implementations of gethostbyname
     (e.g. the Ultrix one and possibly Winsock) don't accept
     dotted-decimal IPv4 addresses.  */
  {
    uint32_t addr_ipv4 = (uint32_t)inet_addr (host);
    if (addr_ipv4 != (uint32_t) -1)
      {
        /* No need to cache host->addr relation, just return the
           address.  */
        char *vec[2];
        vec[0] = (char *)&addr_ipv4;
        vec[1] = NULL;
        return address_list_from_ipv4_addresses (vec);
      }
  }
#else  /* ENABLE_IPV6 */
  /* If we're using getaddrinfo, at least check whether the address is
     already numeric, in which case there is no need to print the
     "Resolving..." output.  (This comes at no additional cost since
     the is_valid_ipv*_address are already required for
     url_parse.)  */
  {
    const char *end = host + strlen (host);
    if (is_valid_ipv4_address (host, end) || is_valid_ipv6_address (host, end))
      numeric_address = true;
  }
#endif

  /* Cache is normally on, but can be turned off with --no-dns-cache.
     Don't cache passive lookups under IPv6.  */
  use_cache = opt.dns_cache;
#ifdef ENABLE_IPV6
  if ((flags & LH_BIND) || numeric_address)
    use_cache = false;
#endif

  /* Try to find the host in the cache so we don't need to talk to the
     resolver.  If LH_REFRESH is requested, remove HOST from the cache
     instead.  */
  if (use_cache)
    {
      if (!(flags & LH_REFRESH))
        {
          al = cache_query (host);
          if (al)
            return al;
        }
      else
        cache_remove (host);
    }

  /* No luck with the cache; resolve HOST. */

  if (!silent && !numeric_address)
    {
      char *str = NULL, *name;

      if (opt.enable_iri && (name = idn_decode ((char *) host)) != NULL)
        {
          str = aprintf ("%s (%s)", name, host);
          xfree (name);
        }

      logprintf (LOG_VERBOSE, _("Resolving %s... "),
                 quotearg_style (escape_quoting_style, str ? str : host));

      xfree (str);
    }

#ifdef ENABLE_IPV6
#ifdef HAVE_LIBCARES
  if (ares)
    {
      struct address_list *al4 = NULL;
      struct address_list *al6 = NULL;

      if (opt.ipv4_only || !opt.ipv6_only)
        ares_gethostbyname (ares, host, AF_INET, callback, &al4);
      if (opt.ipv6_only || !opt.ipv4_only)
        ares_gethostbyname (ares, host, AF_INET6, callback, &al6);

      wait_ares (ares);

      if (al4 && al6)
        al = merge_address_lists (al4, al6);
      else if (al4)
        al = al4;
      else
        al = al6;
    }
  else
#endif
    {
      int err;
      struct addrinfo hints, *res;

      xzero (hints);
      hints.ai_socktype = SOCK_STREAM;
      if (opt.ipv4_only)
        hints.ai_family = AF_INET;
      else if (opt.ipv6_only)
        hints.ai_family = AF_INET6;
      else
        /* We tried using AI_ADDRCONFIG, but removed it because: it
           misinterprets IPv6 loopbacks, it is broken on AIX 5.1, and
           it's unneeded since we sort the addresses anyway.  */
        hints.ai_family = AF_UNSPEC;

      if (flags & LH_BIND)
        hints.ai_flags |= AI_PASSIVE;

#ifdef AI_NUMERICHOST
      if (numeric_address)
        {
          /* Where available, the AI_NUMERICHOST hint can prevent costly
             access to DNS servers.  */
          hints.ai_flags |= AI_NUMERICHOST;
          timeout = 0; /* no timeout needed when "resolving"
                                   numeric hosts -- avoid setting up
                                   signal handlers and such. */
        }
#endif

      err = getaddrinfo_with_timeout (host, NULL, &hints, &res, timeout);

      if (err != 0 || res == NULL)
        {
          if (!silent)
            logprintf (LOG_VERBOSE, _ ("failed: %s.\n"),
                       err != EAI_SYSTEM ? gai_strerror (err) : strerror (errno));
          return NULL;
        }
      al = address_list_from_addrinfo (res);
      freeaddrinfo (res);
    }

  if (!al)
    {
      logprintf (LOG_VERBOSE,
                 _ ("failed: No IPv4/IPv6 addresses for host.\n"));
      return NULL;
    }

  /* Reorder addresses so that IPv4 ones (or IPv6 ones, as per
     --prefer-family) come first.  Sorting is stable so the order of
     the addresses with the same family is undisturbed.  */
  if (al->count > 1 && opt.prefer_family != prefer_none)
    stable_sort (al->addresses, al->count, sizeof (ip_address),
                 opt.prefer_family == prefer_ipv4
                 ? cmp_prefer_ipv4 : cmp_prefer_ipv6);
#else  /* not ENABLE_IPV6 */
#ifdef HAVE_LIBCARES
  if (ares)
    {
      ares_gethostbyname (ares, host, AF_INET, callback, &al);
      wait_ares (ares);
    }
  else
#endif
    {
      struct hostent *hptr = gethostbyname_with_timeout (host, timeout);
      if (!hptr)
        {
          if (!silent)
            {
              if (errno != ETIMEDOUT)
                logprintf (LOG_VERBOSE, _ ("failed: %s.\n"),
                           host_errstr (h_errno));
              else
                logputs (LOG_VERBOSE, _ ("failed: timed out.\n"));
            }
          return NULL;
        }
      /* Do older systems have h_addr_list?  */
      al = address_list_from_ipv4_addresses (hptr->h_addr_list);
    }
#endif /* not ENABLE_IPV6 */

  /* Print the addresses determined by DNS lookup, but no more than
     three if show_all_dns_entries is not specified.  */
  if (!silent && !numeric_address)
    {
      int i;
      int printmax = al->count;

      if (!opt.show_all_dns_entries && printmax > 3)
          printmax = 3;

      for (i = 0; i < printmax; i++)
        {
          logputs (LOG_VERBOSE, print_address (al->addresses + i));
          if (i < printmax - 1)
            logputs (LOG_VERBOSE, ", ");
        }
      if (printmax != al->count)
        logputs (LOG_VERBOSE, ", ...");
      logputs (LOG_VERBOSE, "\n");
    }

  /* Cache the lookup information. */
  if (use_cache)
    cache_store (host, al);

  return al;
}

/* Determine whether a URL is acceptable to be followed, according to
   a list of domains to accept.  */
bool
accept_domain (struct url *u)
{
  assert (u->host != NULL);
  if (opt.domains)
    {
      if (!sufmatch ((const char **)opt.domains, u->host))
        return false;
    }
  if (opt.exclude_domains)
    {
      if (sufmatch ((const char **)opt.exclude_domains, u->host))
        return false;
    }
  return true;
}

/* Check whether WHAT is matched in LIST, each element of LIST being a
   pattern to match WHAT against, using backward matching (see
   match_backwards() in utils.c).

   If an element of LIST matched, 1 is returned, 0 otherwise.  */
bool
sufmatch (const char **list, const char *what)
{
  int i, j, k, lw;

  lw = strlen (what);

  for (i = 0; list[i]; i++)
    {
      j = strlen (list[i]);
      if (lw < j)
        continue; /* what is no (sub)domain of list[i] */

      for (k = lw; j >= 0 && k >= 0; j--, k--)
        if (c_tolower (list[i][j]) != c_tolower (what[k]))
          break;

      /* Domain or subdomain match
       * k == -1: exact match
       * k >= 0 && what[k] == '.': subdomain match
       * k >= 0 && list[i][0] == '.': dot-prefixed subdomain match
       */
      if (j == -1 && (k == -1 || what[k] == '.' || list[i][0] == '.'))
        return true;
    }

  return false;
}

#if defined DEBUG_MALLOC || defined TESTING
void
host_cleanup (void)
{
  if (host_name_addresses_map)
    {
      hash_table_iterator iter;
      for (hash_table_iterate (host_name_addresses_map, &iter);
           hash_table_iter_next (&iter);
           )
        {
          char *host = iter.key;
          struct address_list *al = iter.value;
          xfree (host);
          assert (al->refcount == 1);
          address_list_delete (al);
        }
      hash_table_destroy (host_name_addresses_map);
      host_name_addresses_map = NULL;
    }
}
#endif

bool
is_valid_ip_address (const char *name)
{
  const char *endp;

  endp = name + strlen(name);
  if (is_valid_ipv4_address (name, endp))
    return true;
#ifdef ENABLE_IPV6
  if (is_valid_ipv6_address (name, endp))
    return true;
#endif
  return false;
}