path: root/lib/hostip.c

/***************************************************************************
 *                                  _   _ ____  _     
 *  Project                     ___| | | |  _ \| |    
 *                             / __| | | | |_) | |    
 *                            | (__| |_| |  _ <| |___ 
 *                             \___|\___/|_| \_\_____|
 *
 * Copyright (C) 1998 - 2004, Daniel Stenberg, <daniel@haxx.se>, et al.
 *
 * This software is licensed as described in the file COPYING, which
 * you should have received as part of this distribution. The terms
 * are also available at http://curl.haxx.se/docs/copyright.html.
 * 
 * You may opt to use, copy, modify, merge, publish, distribute and/or sell
 * copies of the Software, and permit persons to whom the Software is
 * furnished to do so, under the terms of the COPYING file.
 *
 * This software is distributed on an "AS IS" basis, WITHOUT WARRANTY OF ANY
 * KIND, either express or implied.
 *
 * $Id$
 ***************************************************************************/

#include "setup.h"

#include <string.h>
#include <errno.h>

#define _REENTRANT

#if defined(WIN32) && !defined(__GNUC__) || defined(__MINGW32__)
#include <malloc.h>
#else
#ifdef HAVE_SYS_TYPES_H
#include <sys/types.h>
#endif
#ifdef HAVE_SYS_SOCKET_H
#include <sys/socket.h>
#endif
#ifdef HAVE_NETINET_IN_H
#include <netinet/in.h>
#endif
#ifdef HAVE_NETDB_H
#include <netdb.h>
#endif
#ifdef HAVE_ARPA_INET_H
#include <arpa/inet.h>
#endif
#ifdef HAVE_STDLIB_H
#include <stdlib.h>	/* required for free() prototypes */
#endif
#ifdef	VMS
#include <in.h>
#include <inet.h>
#include <stdlib.h>
#endif
#endif

#ifdef HAVE_SETJMP_H
#include <setjmp.h>
#endif

#ifdef WIN32
#include <process.h>
#endif

#if (defined(NETWARE) && defined(__NOVELL_LIBC__))
#undef in_addr_t
#define in_addr_t unsigned long
#endif

#include "urldata.h"
#include "sendf.h"
#include "hostip.h"
#include "hash.h"
#include "share.h"
#include "strerror.h"
#include "url.h"

#define _MPRINTF_REPLACE /* use our functions only */
#include <curl/mprintf.h>

#if defined(HAVE_INET_NTOA_R) && !defined(HAVE_INET_NTOA_R_DECL)
#include "inet_ntoa_r.h"
#endif

/* The last #include file should be: */
#ifdef CURLDEBUG
#include "memdebug.h"
#endif

#ifndef ARES_SUCCESS
#define ARES_SUCCESS CURLE_OK
#endif

#define CURL_TIMEOUT_RESOLVE 300 /* when using asynch methods, we allow this
                                    many seconds for a name resolve */

/* These two symbols are for the global DNS cache */
static curl_hash hostname_cache;
static int host_cache_initialized;


static void freednsentry(void *freethis);

/*
 * my_getaddrinfo() is the generic low-level name resolve API within this
 * source file. There exist three versions of this function - for different
 * name resolve layers (selected at build-time). They all take this same set
 * of arguments
 */
static Curl_addrinfo *my_getaddrinfo(struct connectdata *conn,
                                     char *hostname,
                                     int port,
                                     int *waitp);

#if (!defined(HAVE_GETHOSTBYNAME_R) || defined(USE_ARES) || \
     defined(USE_THREADING_GETHOSTBYNAME)) && \
     !defined(ENABLE_IPV6)
static struct hostent* pack_hostent(char** buf, struct hostent* orig);
#endif

#ifdef USE_THREADING_GETHOSTBYNAME
#ifdef DEBUG_THREADING_GETHOSTBYNAME
/* If this is defined, provide tracing */
#define TRACE(args)  \
 do { trace_it("%u: ", __LINE__); trace_it args; } while (0)

static void trace_it (const char *fmt, ...);
#else
#define TRACE(x)
#endif

static bool init_gethostbyname_thread (struct connectdata *conn,
                                       const char *hostname, int port);
struct thread_data {
  HANDLE thread_hnd;
  unsigned thread_id;
  DWORD  thread_status;
  curl_socket_t dummy_sock;   /* dummy for Curl_multi_ares_fdset() */
};
#endif

/*
 * Curl_global_host_cache_init() initializes and sets up a global DNS cache.
 * Global DNS cache is general badness. Do not use. This will be removed in
 * a future version. Use the share interface instead!
 */
void Curl_global_host_cache_init(void)
{
  if (!host_cache_initialized) {
    Curl_hash_init(&hostname_cache, 7, freednsentry);
    host_cache_initialized = 1;
  }
}

/*
 * Return a pointer to the global cache
 */
curl_hash *Curl_global_host_cache_get(void)
{
  return &hostname_cache;
}

/*
 * Destroy and cleanup the global DNS cache
 */
void Curl_global_host_cache_dtor(void)
{
  if (host_cache_initialized) {
    Curl_hash_clean(&hostname_cache);
    host_cache_initialized = 0;
  }
}

/*
 * Minor utility-function:
 * Count the number of characters that an integer takes up.
 */
static int _num_chars(int i)
{
  int chars = 0;

  /* While the number divided by 10 is greater than one, 
   * re-divide the number by 10, and increment the number of 
   * characters by 1.
   *
   * this relies on the fact that for every multiple of 10, 
   * a new digit is added onto every number
   */
  do {
    chars++;

    i = (int) i / 10;
  } while (i >= 1);

  return chars;
}

/*
 * Minor utility-function:
 * Create a hostcache id string for the DNS caching.
 */
static char *
create_hostcache_id(char *server, int port, size_t *entry_len)
{
  char *id = NULL;

  /* Get the length of the new entry id */
  *entry_len = strlen(server) + /* Hostname length */
    1 +                         /* ':' seperator */
    _num_chars(port);     /* number of characters the port will take up */
  
  /* Allocate the new entry id */
  id = malloc(*entry_len + 1); /* 1 extra for the zero terminator */
  if (!id)
    return NULL;

  /* Create the new entry */
  sprintf(id, "%s:%d", server, port);

  return id; /* return pointer to the string */
}

struct hostcache_prune_data {
  int cache_timeout;
  time_t now;
};

/*
 * This function is set as a callback to be called for every entry in the DNS
 * cache when we want to prune old unused entries.
 *
 * Returning non-zero means remove the entry, return 0 to keep it in the
 * cache.
 */
static int
hostcache_timestamp_remove(void *datap, void *hc)
{
  struct hostcache_prune_data *data = 
    (struct hostcache_prune_data *) datap;
  struct Curl_dns_entry *c = (struct Curl_dns_entry *) hc;
  
  if ((data->now - c->timestamp < data->cache_timeout) ||
      c->inuse) {
    /* please don't remove */
    return 0;
  }
  
  /* fine, remove */
  return 1;
}

/*
 * Prune the DNS cache. This assumes that a lock has already been taken.
 */
static void
hostcache_prune(curl_hash *hostcache, int cache_timeout, time_t now)
{
  struct hostcache_prune_data user;

  user.cache_timeout = cache_timeout;
  user.now = now;

  Curl_hash_clean_with_criterium(hostcache, 
                                 (void *) &user, 
                                 hostcache_timestamp_remove);
}

/*
 * Library-wide function for pruning the DNS cache. This function takes and
 * returns the appropriate locks.
 */
void Curl_hostcache_prune(struct SessionHandle *data)
{
  time_t now;

  if(data->set.dns_cache_timeout == -1)
    /* cache forever means never prune! */
    return;

  if(data->share)
    Curl_share_lock(data, CURL_LOCK_DATA_DNS, CURL_LOCK_ACCESS_SINGLE);

  time(&now);

  /* Remove outdated and unused entries from the hostcache */
  hostcache_prune(data->hostcache,
                  data->set.dns_cache_timeout,
                  now);

  if(data->share)
    Curl_share_unlock(data, CURL_LOCK_DATA_DNS);
}

#ifdef HAVE_SIGSETJMP
/* Beware this is a global and unique instance. This is used to store the
   return address that we can jump back to from inside a signal handler. This
   is not thread-safe stuff. */
sigjmp_buf curl_jmpenv;
#endif


/*
 * cache_resolv_response() stores a 'Curl_addrinfo' struct in the DNS cache.
 *
 * When calling Curl_resolv() has resulted in a response with a returned
 * address, we call this function to store the information in the dns
 * cache etc
 *
 * Returns the Curl_dns_entry entry pointer or NULL if the storage failed.
 */
static struct Curl_dns_entry *
cache_resolv_response(struct SessionHandle *data,
                      Curl_addrinfo *addr,
                      char *hostname,
                      int port)
{
  char *entry_id;
  size_t entry_len;
  struct Curl_dns_entry *dns;
  time_t now;

  /* Create an entry id, based upon the hostname and port */
  entry_id = create_hostcache_id(hostname, port, &entry_len);
  /* If we can't create the entry id, fail */
  if (!entry_id)
    return NULL;

  /* Create a new cache entry */
  dns = (struct Curl_dns_entry *) malloc(sizeof(struct Curl_dns_entry));
  if (!dns) {
    Curl_freeaddrinfo(addr);
    free(entry_id);
    return NULL;
  }

  dns->inuse = 0;   /* init to not used */
  dns->addr = addr; /* this is the address(es) */

  /* Store the resolved data in our DNS cache. This function may return a
     pointer to an existing struct already present in the hash, and it may
     return the same argument we pass in. Make no assumptions. */
  dns = Curl_hash_add(data->hostcache, entry_id, entry_len+1, (void *)dns);
  if(!dns) {
    /* Major badness, run away. When this happens, the 'dns' data has
       already been cleared up by Curl_hash_add(). */
    free(entry_id);
    return NULL;
  }
  time(&now);

  dns->timestamp = now; /* used now */
  dns->inuse++;         /* mark entry as in-use */

  /* free the allocated entry_id again */
  free(entry_id);

  return dns;
}

/*
 * Curl_resolv() is the main name resolve function within libcurl. It resolves
 * a name and returns a pointer to the entry in the 'entry' argument (if one
 * is provided). This function might return immediately if we're using asynch
 * resolves. See the return codes.
 *
 * The cache entry we return will get its 'inuse' counter increased when this
 * function is used. You MUST call Curl_resolv_unlock() later (when you're
 * done using this struct) to decrease the counter again.
 *
 * Return codes:
 *
 * -1 = error, no pointer
 * 0 = OK, pointer provided
 * 1 = waiting for response, no pointer
 */
int Curl_resolv(struct connectdata *conn,
                char *hostname,
                int port,
                struct Curl_dns_entry **entry)
{
  char *entry_id = NULL;
  struct Curl_dns_entry *dns = NULL;
  size_t entry_len;
  int wait;
  struct SessionHandle *data = conn->data;
  CURLcode result;

  /* default to failure */
  int rc = -1;
  *entry = NULL;

#ifdef HAVE_SIGSETJMP
  /* this allows us to time-out from the name resolver, as the timeout
     will generate a signal and we will siglongjmp() from that here */
  if(!data->set.no_signal && sigsetjmp(curl_jmpenv, 1)) {
    /* this is coming from a siglongjmp() */
    failf(data, "name lookup timed out");
    return -1;
  }
#endif

  /* Create an entry id, based upon the hostname and port */
  entry_id = create_hostcache_id(hostname, port, &entry_len);
  /* If we can't create the entry id, fail */
  if (!entry_id)
    return -1;

  if(data->share)
    Curl_share_lock(data, CURL_LOCK_DATA_DNS, CURL_LOCK_ACCESS_SINGLE);

  /* See if its already in our dns cache */
  dns = Curl_hash_pick(data->hostcache, entry_id, entry_len+1);
  
  if(data->share)
    Curl_share_unlock(data, CURL_LOCK_DATA_DNS);

  /* free the allocated entry_id again */
  free(entry_id);

  if (!dns) {
    /* The entry was not in the cache. Resolve it to IP address */
      
    /* If my_getaddrinfo() returns NULL, 'wait' might be set to a non-zero
       value indicating that we need to wait for the response to the resolve
       call */
    Curl_addrinfo *addr = my_getaddrinfo(conn, hostname, port, &wait);
    
    if (!addr) {
      if(wait) {
        /* the response to our resolve call will come asynchronously at 
           a later time, good or bad */
        /* First, check that we haven't received the info by now */
        result = Curl_is_resolved(conn, &dns);
        if(result) /* error detected */
          return -1;
        if(dns)
          rc = 0; /* pointer provided */
        else
          rc = 1; /* no info yet */
      }
    }
    else {
      if(data->share)
        Curl_share_lock(data, CURL_LOCK_DATA_DNS, CURL_LOCK_ACCESS_SINGLE);

      /* we got a response, store it in the cache */
      dns = cache_resolv_response(data, addr, hostname, port);
      
      if(data->share)
        Curl_share_unlock(data, CURL_LOCK_DATA_DNS);

      if(!dns)
        /* returned failure, bail out nicely */
        Curl_freeaddrinfo(addr);
      else
        rc = 0;
    }
  }
  else {
    dns->inuse++; /* we use it! */
    rc = 0;
  }

  *entry = dns;

  return rc;
}

/*
 * Curl_resolv_unlock() unlocks the given cached DNS entry. When this has been
 * made, the struct may be destroyed due to pruning. It is important that only
 * one unlock is made for each Curl_resolv() call.
 */
void Curl_resolv_unlock(struct SessionHandle *data, struct Curl_dns_entry *dns)
{
  if(data->share)
    Curl_share_lock(data, CURL_LOCK_DATA_DNS, CURL_LOCK_ACCESS_SINGLE);

  dns->inuse--;

#ifdef CURLDEBUG
  if(dns->inuse < 0) {
    infof(data, "Interal host cache screw-up!");
    *(char **)0=NULL;
  }
#endif

  if(data->share)
    Curl_share_unlock(data, CURL_LOCK_DATA_DNS);
}

/*
 * This is a wrapper function for freeing name information in a protocol
 * independent way. This takes care of using the appropriate underlaying
 * function.
 */
void Curl_freeaddrinfo(Curl_addrinfo *p)
{
#ifdef ENABLE_IPV6
  freeaddrinfo(p);
#else
  free(p); /* works fine for the ARES case too */
#endif
}

/*
 * File-internal: free a cache dns entry.
 */
static void freednsentry(void *freethis)
{
  struct Curl_dns_entry *p = (struct Curl_dns_entry *) freethis;

  Curl_freeaddrinfo(p->addr);

  free(p);
}

/*
 * Curl_mk_dnscache() creates a new DNS cache and returns the handle for it.
 */
curl_hash *Curl_mk_dnscache(void)
{
  return Curl_hash_alloc(7, freednsentry);
}

/* --- resolve name or IP-number --- */

/* Allocate enough memory to hold the full name information structs and
 * everything. OSF1 is known to require at least 8872 bytes. The buffer
 * required for storing all possible aliases and IP numbers is according to
 * Stevens' Unix Network Programming 2nd edition, p. 304: 8192 bytes!
 */
#define CURL_NAMELOOKUP_SIZE 9000

#ifdef USE_ARES

/*
 * Curl_multi_ares_fdset() is called when someone from the outside world
 * (using curl_multi_fdset()) wants to get our fd_set setup and we're talking
 * with ares. The caller must make sure that this function is only called when
 * we have a working ares channel.
 *
 * Returns: CURLE_OK always!
 */

CURLcode Curl_multi_ares_fdset(struct connectdata *conn,
                               fd_set *read_fd_set,
                               fd_set *write_fd_set,
                               int *max_fdp)

{
  int max = ares_fds(conn->data->state.areschannel,
                     read_fd_set, write_fd_set);
  *max_fdp = max;

  return CURLE_OK;
}

/*
 * Curl_is_resolved() is called repeatedly to check if a previous name resolve
 * request has completed. It should also make sure to time-out if the
 * operation seems to take too long.
 *
 * Returns normal CURLcode errors.
 */
CURLcode Curl_is_resolved(struct connectdata *conn,
                          struct Curl_dns_entry **dns)
{
  fd_set read_fds, write_fds;
  struct timeval tv={0,0};
  int count;
  struct SessionHandle *data = conn->data;
  int nfds;

  FD_ZERO(&read_fds);
  FD_ZERO(&write_fds);

  nfds = ares_fds(data->state.areschannel, &read_fds, &write_fds);

  count = select(nfds, &read_fds, &write_fds, NULL,
                 (struct timeval *)&tv);

  /* Call ares_process() unconditonally here, even if we simply timed out
     above, as otherwise the ares name resolve won't timeout! */
  ares_process(data->state.areschannel, &read_fds, &write_fds);

  *dns = NULL;

  if(conn->async.done) {
    /* we're done, kill the ares handle */
    if(!conn->async.dns)
      return CURLE_COULDNT_RESOLVE_HOST;
    *dns = conn->async.dns;
  }

  return CURLE_OK;
}

/*
 * Curl_wait_for_resolv() waits for a resolve to finish. This function should
 * be avoided since using this risk getting the multi interface to "hang".
 *
 * If 'entry' is non-NULL, make it point to the resolved dns entry
 *
 * Returns CURLE_COULDNT_RESOLVE_HOST if the host was not resolved, and
 * CURLE_OPERATION_TIMEDOUT if a time-out occurred.
 */
CURLcode Curl_wait_for_resolv(struct connectdata *conn,
                              struct Curl_dns_entry **entry)
{
  CURLcode rc=CURLE_OK;
  struct SessionHandle *data = conn->data;
  long timeout = CURL_TIMEOUT_RESOLVE; /* default name resolve timeout */

  /* now, see if there's a connect timeout or a regular timeout to
     use instead of the default one */
  if(conn->data->set.connecttimeout)
    timeout = conn->data->set.connecttimeout;
  else if(conn->data->set.timeout)
    timeout = conn->data->set.timeout;

  /* Wait for the name resolve query to complete. */
  while (1) {
    int nfds=0;
    fd_set read_fds, write_fds;
    struct timeval *tvp, tv, store;
    int count;
    struct timeval now = Curl_tvnow();

    store.tv_sec = (int)timeout;
    store.tv_usec = 0;
    
    FD_ZERO(&read_fds);
    FD_ZERO(&write_fds);
    nfds = ares_fds(data->state.areschannel, &read_fds, &write_fds);
    if (nfds == 0)
      /* no file descriptors means we're done waiting */
      break;
    tvp = ares_timeout(data->state.areschannel, &store, &tv);
    count = select(nfds, &read_fds, &write_fds, NULL, tvp);
    if (count < 0 && errno != EINVAL)
      break;

    ares_process(data->state.areschannel, &read_fds, &write_fds);

    timeout -= Curl_tvdiff(Curl_tvnow(), now)/1000; /* spent time */
    if (timeout < 0) {
      /* our timeout, so we cancel the ares operation */
      ares_cancel(data->state.areschannel);
      break;
    }
  }

  /* Operation complete, if the lookup was successful we now have the entry
     in the cache. */
    
  if(entry)
    *entry = conn->async.dns;

  if(!conn->async.dns) {
    /* a name was not resolved */
    if((timeout < 0) || (conn->async.status == ARES_ETIMEOUT)) {
      failf(data, "Resolving host timed out: %s", conn->name);
      rc = CURLE_OPERATION_TIMEDOUT;
    }
    else if(conn->async.done) {
      failf(data, "Could not resolve host: %s (%s)", conn->name,
            ares_strerror(conn->async.status));
      rc = CURLE_COULDNT_RESOLVE_HOST;
    }
    else
      rc = CURLE_OPERATION_TIMEDOUT;

    /* close the connection, since we can't return failure here without
       cleaning up this connection properly */
    Curl_disconnect(conn);
  }
  
  return rc;
}
#endif

#if defined(USE_ARES) || defined(USE_THREADING_GETHOSTBYNAME)

/*
 * host_callback() gets called by ares/gethostbyname_thread() when we got the
 * name resolved (or not!).
 *
 * If the status argument is ARES_SUCCESS, we must copy the hostent field
 * since ares will free it when this function returns. This operation stores
 * the resolved data in the DNS cache.
 *
 * The storage operation locks and unlocks the DNS cache.
 */
static void host_callback(void *arg, /* "struct connectdata *" */
                          int status,
                          struct hostent *hostent)
{
  struct connectdata *conn = (struct connectdata *)arg;
  struct Curl_dns_entry *dns = NULL;

  conn->async.done = TRUE;
  conn->async.status = status;

  if(ARES_SUCCESS == status) {
    /* we got a resolved name in 'hostent' */
    char *bufp = (char *)malloc(CURL_NAMELOOKUP_SIZE);
    if(bufp) {

      /* pack_hostent() copies to and shrinks the target buffer */
      struct hostent *he = pack_hostent(&bufp, hostent);

      struct SessionHandle *data = conn->data;

      if(data->share)
        Curl_share_lock(data, CURL_LOCK_DATA_DNS, CURL_LOCK_ACCESS_SINGLE);

      dns = cache_resolv_response(data, he,
                                  conn->async.hostname, conn->async.port);

      if(data->share)
        Curl_share_unlock(data, CURL_LOCK_DATA_DNS);
    }
  }

  conn->async.dns = dns;

  /* The input hostent struct will be freed by ares when we return from this
     function */
}
#endif

#ifdef USE_ARES
/*
 * my_getaddrinfo() when using ares for name resolves.
 *
 * Returns name information about the given hostname and port number. If
 * successful, the 'hostent' is returned and the forth argument will point to
 * memory we need to free after use. That memory *MUST* be freed with
 * Curl_freeaddrinfo(), nothing else.
 */
static Curl_addrinfo *my_getaddrinfo(struct connectdata *conn,
                                     char *hostname,
                                     int port,
                                     int *waitp)
{
  char *bufp;
  struct SessionHandle *data = conn->data;

  *waitp = FALSE;
  
  bufp = strdup(hostname);

  if(bufp) {
    Curl_safefree(conn->async.hostname);
    conn->async.hostname = bufp;
    conn->async.port = port;
    conn->async.done = FALSE; /* not done */
    conn->async.status = 0;   /* clear */
    conn->async.dns = NULL;   /* clear */

    /* areschannel is already setup in the Curl_open() function */
    ares_gethostbyname(data->state.areschannel, hostname, PF_INET,
                       host_callback, conn);
      
    *waitp = TRUE; /* please wait for the response */
  }
  return NULL; /* no struct yet */
}
#endif

#if !defined(USE_ARES) && !defined(USE_THREADING_GETHOSTBYNAME)

/*
 * Curl_wait_for_resolv() for builds without ARES and threaded gethostbyname,
 * Curl_resolv() can never return wait==TRUE, so this function will never be
 * called. If it still gets called, we return failure at once.
 *
 * We provide this function only to allow multi.c to remain unaware if we are
 * doing asynch resolves or not.
 */
CURLcode Curl_wait_for_resolv(struct connectdata *conn,
                              struct Curl_dns_entry **entry)
{
  (void)conn;
  *entry=NULL;
  return CURLE_COULDNT_RESOLVE_HOST;
}

/*
 * This function will never be called when built with ares or threaded
 * resolves. If it still gets called, we return failure at once.
 *
 * We provide this function only to allow multi.c to remain unaware if we are
 * doing asynch resolves or not.
 */
CURLcode Curl_is_resolved(struct connectdata *conn,
                          struct Curl_dns_entry **dns)
{
  (void)conn;
  *dns = NULL;

  return CURLE_COULDNT_RESOLVE_HOST;
}
#endif

#if !defined(USE_ARES)
/*
 * Non-ares build. If we are using threading gethostbyname, then this must
 * set the fd_set for the threaded resolve socket. If not, we just return OK.
 */
CURLcode Curl_multi_ares_fdset(struct connectdata *conn,
                               fd_set *read_fd_set,
                               fd_set *write_fd_set,
                               int *max_fdp)
{
#ifdef USE_THREADING_GETHOSTBYNAME
  const struct thread_data *td =
    (const struct thread_data *) conn->async.os_specific;

  if (td && td->dummy_sock != CURL_SOCKET_BAD) {
    FD_SET(td->dummy_sock,write_fd_set);
    *max_fdp = td->dummy_sock;
  }
#else /* if not USE_THREADING_GETHOSTBYNAME */
  (void)conn;
  (void)read_fd_set;
  (void)write_fd_set;
  (void)max_fdp;
#endif
  return CURLE_OK;
}
#endif /* !USE_ARES */

#if defined(ENABLE_IPV6) && !defined(USE_ARES)

#ifdef CURLDEBUG
/* These two are strictly for memory tracing and are using the same
 * style as the family otherwise present in memdebug.c. I put these ones
 * here since they require a bunch of struct types I didn't wanna include
 * in memdebug.c
 */
int curl_getaddrinfo(char *hostname, char *service,
                     struct addrinfo *hints,
                     struct addrinfo **result,
                     int line, const char *source)
{
  int res=(getaddrinfo)(hostname, service, hints, result);
  if(0 == res) {
    /* success */
    if(logfile)
      fprintf(logfile, "ADDR %s:%d getaddrinfo() = %p\n",
              source, line, (void *)*result);
  }
  else {
    if(logfile)
      fprintf(logfile, "ADDR %s:%d getaddrinfo() failed\n",
              source, line);
  }
  return res;
}

void curl_freeaddrinfo(struct addrinfo *freethis,
                       int line, const char *source)
{
  (freeaddrinfo)(freethis);
  if(logfile)
    fprintf(logfile, "ADDR %s:%d freeaddrinfo(%p)\n",
            source, line, (void *)freethis);
}

#endif

/*
 * my_getaddrinfo() when built ipv6-enabled.
 *
 * Returns name information about the given hostname and port number. If
 * successful, the 'addrinfo' is returned and the forth argument will point to
 * memory we need to free after use. That memory *MUST* be freed with
 * Curl_freeaddrinfo(), nothing else.
 */
static Curl_addrinfo *my_getaddrinfo(struct connectdata *conn,
                                     char *hostname,
                                     int port,
                                     int *waitp)
{
  struct addrinfo hints, *res;
  int error;
  char sbuf[NI_MAXSERV];
  int s, pf;
  struct SessionHandle *data = conn->data;

  *waitp=0; /* don't wait, we have the response now */

  /* see if we have an IPv6 stack */
  s = socket(PF_INET6, SOCK_DGRAM, 0);
  if (s < 0)
    /* Some non-IPv6 stacks have been found to make very slow name resolves
     * when PF_UNSPEC is used, so thus we switch to a mere PF_INET lookup if
     * the stack seems to be a non-ipv6 one. */
    pf = PF_INET;
  else {
    /* This seems to be an IPv6-capable stack, use PF_UNSPEC for the widest
     * possible checks. And close the socket again.
     */
    sclose(s);

    /*
     * Check if a more limited name resolve has been requested.
     */
    switch(data->set.ip_version) {
    case CURL_IPRESOLVE_V4:
      pf = PF_INET;
      break;
    case CURL_IPRESOLVE_V6:
      pf = PF_INET6;
      break;
    default:
      pf = PF_UNSPEC;
      break;
    }
  }
 
  memset(&hints, 0, sizeof(hints));
  hints.ai_family = pf;
  hints.ai_socktype = SOCK_STREAM;
  hints.ai_flags = AI_CANONNAME;
  snprintf(sbuf, sizeof(sbuf), "%d", port);
  error = getaddrinfo(hostname, sbuf, &hints, &res);
  if (error) {
    infof(data, "getaddrinfo(3) failed for %s:%d\n", hostname, port);    
    return NULL;
  }

  return res;
}
#else /* following code is IPv4-only */

#if !defined(HAVE_GETHOSTBYNAME_R) || defined(USE_ARES) || \
    defined(USE_THREADING_GETHOSTBYNAME)
static void hostcache_fixoffset(struct hostent *h, long offset);

/*
 * pack_hostent() is a file-local function that performs a "deep" copy of a
 * hostent into a buffer (returns a pointer to the copy). Make absolutely sure
 * the destination buffer is big enough!
 */
static struct hostent* pack_hostent(char** buf, struct hostent* orig)
{
  char *bufptr;
  char *newbuf;
  struct hostent* copy;

  int i;
  char *str;
  size_t len;

  bufptr = *buf;
  copy = (struct hostent*)bufptr;

  bufptr += sizeof(struct hostent);
  copy->h_name = bufptr;
  len = strlen(orig->h_name) + 1;
  strncpy(bufptr, orig->h_name, len);
  bufptr += len;

  /* we align on even 64bit boundaries for safety */
#define MEMALIGN(x) ((x)+(8-(((unsigned long)(x))&0x7)))

  /* This must be aligned properly to work on many CPU architectures! */
  bufptr = MEMALIGN(bufptr);
  
  copy->h_aliases = (char**)bufptr;

  /* Figure out how many aliases there are */
  for (i = 0; orig->h_aliases && orig->h_aliases[i]; ++i);

  /* Reserve room for the array */
  bufptr += (i + 1) * sizeof(char*);

  /* Clone all known aliases */
  if(orig->h_aliases) {
    for(i = 0; (str = orig->h_aliases[i]); i++) {
      len = strlen(str) + 1;
      strncpy(bufptr, str, len);
      copy->h_aliases[i] = bufptr;
      bufptr += len;
    }
  }
  /* if(!orig->h_aliases) i was already set to 0 */

  /* Terminate the alias list with a NULL */
  copy->h_aliases[i] = NULL;

  copy->h_addrtype = orig->h_addrtype;
  copy->h_length = orig->h_length;
    
  /* align it for (at least) 32bit accesses */
  bufptr = MEMALIGN(bufptr);

  copy->h_addr_list = (char**)bufptr;

  /* Figure out how many addresses there are */
  for (i = 0; orig->h_addr_list[i] != NULL; ++i);

  /* Reserve room for the array */
  bufptr += (i + 1) * sizeof(char*);

  i = 0;
  len = orig->h_length;
  str = orig->h_addr_list[i];
  while (str != NULL) {
    memcpy(bufptr, str, len);
    copy->h_addr_list[i] = bufptr;
    bufptr += len;
    str = orig->h_addr_list[++i];
  }
  copy->h_addr_list[i] = NULL;

  /* now, shrink the allocated buffer to the size we actually need, which
     most often is only a fraction of the original alloc */
  newbuf=(char *)realloc(*buf, (long)(bufptr-*buf));

  /* if the alloc moved, we need to adjust things again */
  if(newbuf != *buf)
    hostcache_fixoffset((struct hostent*)newbuf, (long)(newbuf-*buf));

  /* setup the return */
  *buf = newbuf;
  copy = (struct hostent*)newbuf;

  return copy;
}
#endif

/*
 * hostcache_fixoffset() is a utility-function that corrects all pointers in
 * the given hostent struct according to the offset. This is typically used
 * when a hostent has been reallocated and needs to be setup properly on the
 * new address.
 */
static void hostcache_fixoffset(struct hostent *h, long offset)
{
  int i=0;

  h->h_name=(char *)((long)h->h_name+offset);
  if(h->h_aliases) {
    /* only relocate aliases if there are any! */
    h->h_aliases=(char **)((long)h->h_aliases+offset);
    while(h->h_aliases[i]) {
      h->h_aliases[i]=(char *)((long)h->h_aliases[i]+offset);
      i++;
    }
  }

  h->h_addr_list=(char **)((long)h->h_addr_list+offset);
  i=0;
  while(h->h_addr_list[i]) {
    h->h_addr_list[i]=(char *)((long)h->h_addr_list[i]+offset);
    i++;
  }
}

#ifndef USE_ARES

/*
 * MakeIP() converts the input binary ipv4-address to an ascii string in the
 * dotted numerical format. 'addr' is a pointer to a buffer that is 'addr_len'
 * bytes big. 'num' is the 32 bit IP number.
 */
static char *MakeIP(unsigned long num, char *addr, int addr_len)
{
#if defined(HAVE_INET_NTOA) || defined(HAVE_INET_NTOA_R)
  struct in_addr in;
  in.s_addr = htonl(num);

#if defined(HAVE_INET_NTOA_R)
  inet_ntoa_r(in,addr,addr_len);
#else
  strncpy(addr,inet_ntoa(in),addr_len);
#endif
#else
  unsigned char *paddr;

  num = htonl(num);  /* htonl() added to avoid endian probs */
  paddr = (unsigned char *)&num;
  sprintf(addr, "%u.%u.%u.%u", paddr[0], paddr[1], paddr[2], paddr[3]);
#endif
  return (addr);
}

/*
 * my_getaddrinfo() - the ipv4 "traditional" version.
 *
 * The original code to this function was once stolen from the Dancer source
 * code, written by Bjorn Reese, it has since been patched and modified
 * considerably.
 */
static Curl_addrinfo *my_getaddrinfo(struct connectdata *conn,
                                     char *hostname,
                                     int port,
                                     int *waitp)
{
  struct hostent *h = NULL;
  in_addr_t in;
  struct SessionHandle *data = conn->data;
  (void)port; /* unused in IPv4 code */

  *waitp = 0; /* don't wait, we act synchronously */

  in=inet_addr(hostname);
  if (in != CURL_INADDR_NONE) {
    struct in_addr *addrentry;
    struct namebuf {
        struct hostent hostentry;
        char *h_addr_list[2];
        struct in_addr addrentry;
        char h_name[128];
    } *buf = (struct namebuf *)malloc(sizeof(struct namebuf));
    if(!buf)
      return NULL; /* major failure */

    h = &buf->hostentry;
    h->h_addr_list = &buf->h_addr_list[0];
    addrentry = &buf->addrentry;
    addrentry->s_addr = in;
    h->h_addr_list[0] = (char*)addrentry;
    h->h_addr_list[1] = NULL;
    h->h_addrtype = AF_INET;
    h->h_length = sizeof(*addrentry);
    h->h_name = &buf->h_name[0];
    MakeIP(ntohl(in), (char *)h->h_name, sizeof(buf->h_name));
  }
#if defined(HAVE_GETHOSTBYNAME_R)
  else {
    int h_errnop;
    int res=ERANGE;
    int step_size=200;
    int *buf = (int *)malloc(CURL_NAMELOOKUP_SIZE);
    if(!buf)
      return NULL; /* major failure */

     /* Workaround for gethostbyname_r bug in qnx nto. It is also _required_
        for some of these functions. */
    memset(buf, 0, CURL_NAMELOOKUP_SIZE);
#ifdef HAVE_GETHOSTBYNAME_R_5
    /* Solaris, IRIX and more */
    (void)res; /* prevent compiler warning */
    while(!h) {
      h = gethostbyname_r(hostname,
                          (struct hostent *)buf,
                          (char *)buf + sizeof(struct hostent),
                          step_size - sizeof(struct hostent),
                          &h_errnop);

      /* If the buffer is too small, it returns NULL and sets errno to
         ERANGE. The errno is thread safe if this is compiled with
         -D_REENTRANT as then the 'errno' variable is a macro defined to
         get used properly for threads. */

      if(h || (errno != ERANGE))
        break;
      
      step_size+=200;
    }

#ifdef CURLDEBUG
    infof(data, "gethostbyname_r() uses %d bytes\n", step_size);
#endif

    if(h) {
      int offset;
      h=(struct hostent *)realloc(buf, step_size);
      offset=(long)h-(long)buf;
      hostcache_fixoffset(h, offset);
      buf=(int *)h;
    }
    else
#endif /* HAVE_GETHOSTBYNAME_R_5 */
#ifdef HAVE_GETHOSTBYNAME_R_6
    /* Linux */
    do {
      res=gethostbyname_r(hostname,
			  (struct hostent *)buf,
			  (char *)buf + sizeof(struct hostent),
			  step_size - sizeof(struct hostent),
			  &h, /* DIFFERENCE */
			  &h_errnop);
      /* Redhat 8, using glibc 2.2.93 changed the behavior. Now all of a
         sudden this function returns EAGAIN if the given buffer size is too
         small. Previous versions are known to return ERANGE for the same
         problem.

         This wouldn't be such a big problem if older versions wouldn't
         sometimes return EAGAIN on a common failure case. Alas, we can't
         assume that EAGAIN *or* ERANGE means ERANGE for any given version of
         glibc.

         For now, we do that and thus we may call the function repeatedly and
         fail for older glibc versions that return EAGAIN, until we run out
         of buffer size (step_size grows beyond CURL_NAMELOOKUP_SIZE).

         If anyone has a better fix, please tell us!

         -------------------------------------------------------------------

         On October 23rd 2003, Dan C dug up more details on the mysteries of
         gethostbyname_r() in glibc:

         In glibc 2.2.5 the interface is different (this has also been
         discovered in glibc 2.1.1-6 as shipped by Redhat 6). What I can't
         explain, is that tests performed on glibc 2.2.4-34 and 2.2.4-32
         (shipped/upgraded by Redhat 7.2) don't show this behavior!

         In this "buggy" version, the return code is -1 on error and 'errno'
         is set to the ERANGE or EAGAIN code. Note that 'errno' is not a
         thread-safe variable.

      */

      if(((ERANGE == res) || (EAGAIN == res)) ||
         ((res<0) && ((ERANGE == errno) || (EAGAIN == errno))))
	step_size+=200;
      else
        break;
    } while(step_size <= CURL_NAMELOOKUP_SIZE);

    if(!h) /* failure */
      res=1;
    
#ifdef CURLDEBUG
    infof(data, "gethostbyname_r() uses %d bytes\n", step_size);
#endif
    if(!res) {
      int offset;
      h=(struct hostent *)realloc(buf, step_size);
      offset=(long)h-(long)buf;
      hostcache_fixoffset(h, offset);
      buf=(int *)h;
    }
    else
#endif/* HAVE_GETHOSTBYNAME_R_6 */
#ifdef HAVE_GETHOSTBYNAME_R_3
    /* AIX, Digital Unix/Tru64, HPUX 10, more? */

    /* For AIX 4.3 or later, we don't use gethostbyname_r() at all, because of
       the plain fact that it does not return unique full buffers on each
       call, but instead several of the pointers in the hostent structs will
       point to the same actual data! This have the unfortunate down-side that
       our caching system breaks down horribly. Luckily for us though, AIX 4.3
       and more recent versions have a completely thread-safe libc where all
       the data is stored in thread-specific memory areas making calls to the
       plain old gethostbyname() work fine even for multi-threaded programs.
       
       This AIX 4.3 or later detection is all made in the configure script.

       Troels Walsted Hansen helped us work this out on March 3rd, 2003. */

    if(CURL_NAMELOOKUP_SIZE >=
       (sizeof(struct hostent)+sizeof(struct hostent_data))) {

      /* August 22nd, 2000: Albert Chin-A-Young brought an updated version
       * that should work! September 20: Richard Prescott worked on the buffer
       * size dilemma. */

      res = gethostbyname_r(hostname,
                            (struct hostent *)buf,
                            (struct hostent_data *)((char *)buf +
                                                    sizeof(struct hostent)));
      h_errnop= errno; /* we don't deal with this, but set it anyway */
    }
    else
      res = -1; /* failure, too smallish buffer size */

    if(!res) { /* success */

      h = (struct hostent*)buf; /* result expected in h */

      /* This is the worst kind of the different gethostbyname_r() interfaces.
         Since we don't know how big buffer this particular lookup required,
         we can't realloc down the huge alloc without doing closer analysis of
         the returned data. Thus, we always use CURL_NAMELOOKUP_SIZE for every
         name lookup. Fixing this would require an extra malloc() and then
         calling pack_hostent() that subsequent realloc()s down the new memory
         area to the actually used amount. */
    }    
    else
#endif /* HAVE_GETHOSTBYNAME_R_3 */
      {
      infof(data, "gethostbyname_r(2) failed for %s\n", hostname);
      h = NULL; /* set return code to NULL */
      free(buf);
    }
#else /* HAVE_GETHOSTBYNAME_R */
  else {

#ifdef USE_THREADING_GETHOSTBYNAME
    /* fire up a new resolver thread! */
    if (init_gethostbyname_thread(conn,hostname,port)) {
      *waitp = TRUE;  /* please wait for the response */
      return NULL;
    }
    infof(data, "init_gethostbyname_thread() failed for %s; code %lu\n",
          hostname, GetLastError());
#endif
    h = gethostbyname(hostname);
    if (!h)
      infof(data, "gethostbyname(2) failed for %s\n", hostname);
    else {
      char *buf=(char *)malloc(CURL_NAMELOOKUP_SIZE);
      /* we make a copy of the hostent right now, right here, as the static
         one we got a pointer to might get removed when we don't want/expect
         that */
      h = pack_hostent(&buf, h);
    }
#endif /*HAVE_GETHOSTBYNAME_R */
  }

  return h;
}

#endif /* end of IPv4-specific code */

#endif /* end of !USE_ARES */


#if defined(USE_THREADING_GETHOSTBYNAME)
#ifdef DEBUG_THREADING_GETHOSTBYNAME
static void trace_it (const char *fmt, ...)
{
  static int do_trace = -1;
  va_list args;

  if (do_trace == -1) {
    const char *env = getenv("CURL_TRACE");
    do_trace = (env && atoi(env) > 0);
  }
  if (!do_trace)
    return;
  va_start (args, fmt);
  vfprintf (stderr, fmt, args);
/*fflush (stderr); */  /* seems a bad idea in a multi-threaded app */
  va_end (args);
}
#endif

/*
 * gethostbyname_thread() resolves a name, calls the host_callback and then
 * exits.
 *
 * For builds without ARES/USE_IPV6, create a resolver thread and wait on it.
 */
static unsigned __stdcall gethostbyname_thread (void *arg)
{
  struct connectdata *conn = (struct connectdata*) arg;
  struct hostent *he;
  int    rc;

  WSASetLastError (conn->async.status = NO_DATA); /* pending status */
  he = gethostbyname (conn->async.hostname);
  if (he) {
    host_callback(conn, ARES_SUCCESS, he);
    rc = 1;
  }
  else {
    host_callback(conn, (int)WSAGetLastError(), NULL);
    rc = 0;
  }
  TRACE(("Winsock-error %d, addr %s\n", conn->async.status,
         he ? inet_ntoa(*(struct in_addr*)he->h_addr) : "unknown"));
  return (rc);
  /* An implicit _endthreadex() here */
}

/*
 * destroy_thread_data() cleans up async resolver data.
 * Complementary of ares_destroy.
 */
static void destroy_thread_data (struct Curl_async *async)
{
  if (async->hostname)
    free(async->hostname);

  if (async->os_specific) {
    curl_socket_t sock = ((const struct thread_data*)async->os_specific)->dummy_sock;

    if (sock != CURL_SOCKET_BAD)
       sclose(sock);
    free(async->os_specific);
  }
  async->hostname = NULL;
  async->os_specific = NULL;
}

/*
 * init_gethostbyname_thread() starts a new thread that performs
 * the actual resolve. This function returns before the resolve is done.
 */
static bool init_gethostbyname_thread (struct connectdata *conn,
                                       const char *hostname, int port)
{
  struct thread_data *td = calloc(sizeof(*td), 1);

  if (!td) {
    SetLastError(ENOMEM);
    return (0);
  }

  Curl_safefree(conn->async.hostname);
  conn->async.hostname = strdup(hostname);
  if (!conn->async.hostname) {
    free(td);
    SetLastError(ENOMEM);
    return (0);
  }

  conn->async.port = port;
  conn->async.done = FALSE;
  conn->async.status = 0;
  conn->async.dns = NULL;
  conn->async.os_specific = (void*) td;

  td->dummy_sock = CURL_SOCKET_BAD;
  td->thread_hnd = (HANDLE) _beginthreadex(NULL, 0, gethostbyname_thread,
                                conn, 0, &td->thread_id);
  if (!td->thread_hnd) {
     SetLastError(errno);
     TRACE(("_beginthreadex() failed; %s\n", Curl_strerror(conn,errno)));
     destroy_thread_data(&conn->async);
     return (0);
  }
  /* This socket is only to keep Curl_multi_ares_fdset() and select() happy;
   * should never become signalled for read/write since it's unbound but
   * Windows needs atleast 1 socket in select().
   */
  td->dummy_sock = socket(AF_INET, SOCK_DGRAM, 0);
  return (1);
}

/*
 * Curl_wait_for_resolv() waits for a resolve to finish. This function should
 * be avoided since using this risk getting the multi interface to "hang".
 *
 * If 'entry' is non-NULL, make it point to the resolved dns entry
 *
 * This is the version for resolves-in-a-thread.
 */
CURLcode Curl_wait_for_resolv(struct connectdata *conn,
                              struct Curl_dns_entry **entry)
{
  struct thread_data   *td = (struct thread_data*) conn->async.os_specific;
  struct SessionHandle *data = conn->data;
  long   timeout;
  DWORD  status, ticks;
  CURLcode rc;

  curlassert (conn && td);

  /* now, see if there's a connect timeout or a regular timeout to
     use instead of the default one */
  timeout =
    conn->data->set.connecttimeout ? conn->data->set.connecttimeout :
    conn->data->set.timeout ? conn->data->set.timeout :
    CURL_TIMEOUT_RESOLVE; /* default name resolve timeout */
  ticks = GetTickCount();

  status = WaitForSingleObject(td->thread_hnd, 1000UL*timeout);
  if (status == WAIT_OBJECT_0 || status == WAIT_ABANDONED) {
     /* Thread finished before timeout; propagate Winsock error to this thread.
      * 'conn->async.done = TRUE' is set in host_callback().
      */
     WSASetLastError(conn->async.status);
     GetExitCodeThread(td->thread_hnd, &td->thread_status);
     TRACE(("gethostbyname_thread() status %lu, thread retval %lu, ",
            status, td->thread_status));
  }
  else {
     conn->async.done = TRUE;
     td->thread_status = (DWORD)-1;
     TRACE(("gethostbyname_thread() timeout, "));
  }

  TRACE(("elapsed %lu ms\n", GetTickCount()-ticks));

  CloseHandle(td->thread_hnd);

  if(entry)
    *entry = conn->async.dns;

  rc = CURLE_OK;

  if (!conn->async.dns) {
    /* a name was not resolved */
    if (td->thread_status == (DWORD)-1 || conn->async.status == NO_DATA) {
      failf(data, "Resolving host timed out: %s", conn->name);
      rc = CURLE_OPERATION_TIMEDOUT;
    }
    else if(conn->async.done) {
      failf(data, "Could not resolve host: %s; %s",
            conn->name, Curl_strerror(conn,conn->async.status));
      rc = CURLE_COULDNT_RESOLVE_HOST;
    }
    else
      rc = CURLE_OPERATION_TIMEDOUT;

    destroy_thread_data(&conn->async);
    /* close the connection, since we can't return failure here without
       cleaning up this connection properly */
    Curl_disconnect(conn);
  }
  return (rc);
}

/*
 * Curl_is_resolved() is called repeatedly to check if a previous name resolve
 * request has completed. It should also make sure to time-out if the
 * operation seems to take too long.
 */
CURLcode Curl_is_resolved(struct connectdata *conn,
                          struct Curl_dns_entry **entry)
{
  *entry = NULL;

  if (conn->async.done) {
    /* we're done */
    destroy_thread_data(&conn->async);
    if (!conn->async.dns) {
      TRACE(("Curl_is_resolved(): CURLE_COULDNT_RESOLVE_HOST\n"));
      return CURLE_COULDNT_RESOLVE_HOST;
    }
    *entry = conn->async.dns;
    TRACE(("resolved okay, dns %p\n", *entry));
  }
  else
    TRACE(("not yet\n"));
  return CURLE_OK;
}

#endif