glibc/resolv/nss_dns/dns-canon.c

/* Copyright (C) 2004 Free Software Foundation, Inc.
   This file is part of the GNU C Library.
   Contributed by Ulrich Drepper <drepper@redhat.com>, 2004.

   The GNU C Library is free software; you can redistribute it and/or
   modify it under the terms of the GNU Lesser General Public
   License as published by the Free Software Foundation; either
   version 2.1 of the License, or (at your option) any later version.

   The GNU C Library 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
   Lesser General Public License for more details.

   You should have received a copy of the GNU Lesser General Public
   License along with the GNU C Library; if not, write to the Free
   Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
   02111-1307 USA.  */

#include <errno.h>
#include <netdb.h>
#include <resolv.h>
#include <stdlib.h>
#include <arpa/nameser.h>
#include <nsswitch.h>


#if PACKETSZ > 65536
# define MAXPACKET	PACKETSZ
#else
# define MAXPACKET	65536
#endif


/* We need this time later.  */
typedef union querybuf
{
  HEADER hdr;
  unsigned char buf[MAXPACKET];
} querybuf;


enum nss_status
_nss_dns_getcanonname_r (const char *name, char *buffer, size_t buflen,
			 char **result,int *errnop, int *h_errnop)
{
  /* Just an alibi buffer, res_nquery will allocate a real buffer for
     us.  */
  unsigned char buf[20];
  union
  {
    querybuf *buf;
    unsigned char *ptr;
  } ansp = { .ptr = buf };
  enum nss_status status;

  int r = __libc_res_nquery (&_res, name, ns_c_in, ns_t_cname,
			     buf, sizeof (buf), &ansp.ptr);
  if (r > 0)
    {
      /* We need to decode the response.  Just one question record.
	 And if we got no answers we bail out, too.  */
      if (ansp.buf->hdr.qdcount != htons (1)
	  || ansp.buf->hdr.ancount == 0)
	goto unavail;

      /* Beginning and end of the buffer with query, answer, and the
	 rest.  */
      unsigned char *ptr = &ansp.buf->buf[sizeof (HEADER)];
      unsigned char *endptr = ansp.ptr + r;

      /* Skip over the query.  This is the name, type, and class.  */
      int s = __dn_skipname (ptr, endptr);
      if (s < 0)
	goto unavail;

      /* Skip over the name and the two 16-bit values containing type
	 and class.  */
      ptr += s + 2 * sizeof (uint16_t);

      /* Now the reply.  First again the name from the query, then
	 type, class, TTL, and the length of the RDATA.  */
      s = __dn_skipname (ptr, endptr);
      if (s < 0)
	goto unavail;

      ptr += s;

      /* Check whether type and class match.  */
      if (*(uint16_t *) ptr != htons (ns_t_cname))
	goto unavail;

      ptr += sizeof (uint16_t);
      if (*(uint16_t *) ptr != htons (ns_c_in))
	goto unavail;

      /* Also skip over the TTL and rdata length.  */
      ptr += sizeof (uint16_t) + sizeof (uint32_t) + sizeof (int16_t);

      /* Now the name we are looking for.  */
      s = __dn_expand (ansp.buf->buf, endptr, ptr, buffer, buflen);
      if (s < 0)
	{
	  if (errno != EMSGSIZE)
	    goto unavail;

	  /* The buffer is too small.  */
	  *errnop = ERANGE;
	  status = NSS_STATUS_TRYAGAIN;
	  h_errno = NETDB_INTERNAL;
	}
      else
	{
	  /* Success.  */
	  *result = buffer;
	  status = NSS_STATUS_SUCCESS;
	}
    }
  else if (h_errno == TRY_AGAIN)
    {
    again:
      status = NSS_STATUS_TRYAGAIN;
      *errnop = errno;
    }
  else
    {
    unavail:
      status = NSS_STATUS_UNAVAIL;
      *errnop = errno;
    }
  *h_errnop = h_errno;

  if (ansp.ptr != buf)
    free (ansp.ptr);

  return status;
}