hostip.c

    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, 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. */

      ret = gethostbyname_r(hostname,
                            (struct hostent *)buf,
                            (struct hostent_data *)((char *)buf +
                                                    sizeof(struct hostent)));
    else
      ret = -1; /* failure, too smallish buffer size */
    
    /* result expected in h */
    h = (struct hostent*)buf;
    h_errnop= errno; /* we don't deal with this, but set it anyway */
    if(ret)
#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 {
    if ((h = gethostbyname(hostname)) == NULL ) {
      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 */