hostip.c

         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
    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)
static void trace_it (const char *fmt, ...)
{
  static int do_trace = -1;
  va_list args;

  if (do_trace == -1)
     do_trace = getenv("CURL_TRACE") ? 1 : 0;
  if (!do_trace)
     return;
  va_start (args, fmt);
  vfprintf (stderr, fmt, args);
  fflush (stderr);
  va_end (args);
}

/* For builds without ARES/USE_IPV6, create a resolver thread and wait on it.
 */
static DWORD WINAPI 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 ExitThread() here */
}

/* complementary of ares_destroy
 */
static void destroy_thread_data (struct connectdata *conn)
{
  if (conn->async.hostname)
     free(conn->async.hostname);
  if (conn->async.os_specific)
     free(conn->async.os_specific);
  conn->async.hostname = NULL;
  conn->async.os_specific = NULL;
}

static bool init_gethostbyname_thread (struct connectdata *conn,
                                       const char *hostname, int port)
{
  struct thread_data *td = malloc(sizeof(*td));

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

  memset (td, 0, sizeof(*td));
  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->thread_hnd = CreateThread(NULL, 0, gethostbyname_thread,
                                conn, 0, &td->thread_id);
  if (!td->thread_hnd) {
     TRACE(("CreateThread() failed; %lu\n", GetLastError()));
     destroy_thread_data(conn);
     return (0);
  }
  return (1);
}

/* called to check if the name is resolved now */
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 :
            300;   /* default name resolve timeout in seconds */
  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 */
     WSASetLastError(conn->async.status);
     GetExitCodeThread(td->thread_hnd, &td->thread_status);
     TRACE(("status %lu, thread-status %08lX\n", status, td->thread_status));
  }
  else {
     conn->async.done = TRUE;
     TerminateThread(td->thread_hnd, (DWORD)-1);
     td->thread_status = (DWORD)-1;
  }

  TRACE(("gethostbyname_thread() retval %08lX, elapsed %lu ms\n",
         td->thread_status, GetTickCount()-ticks));

  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 (code %lu)", conn->name, conn->async.status);
      rc = CURLE_COULDNT_RESOLVE_HOST;
    }
    else
      rc = CURLE_OPERATION_TIMEDOUT;

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

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);
    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