/* Copyright (C) 2004-2018 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, see

   <http://www.gnu.org/licenses/>.  */

#include <errno.h>

#include <netdb.h>

#include <resolv.h>

#include <stdlib.h>

#include <stdint.h>

#include <arpa/nameser.h>

#include <nsswitch.h>

#include <resolv/resolv_context.h>

#include <resolv/resolv-internal.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;

static const short int qtypes[] = { ns_t_a, ns_t_aaaa };

#define nqtypes (sizeof (qtypes) / sizeof (qtypes[0]))

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 = NSS_STATUS_UNAVAIL;

  struct resolv_context *ctx = __resolv_context_get ();

  if (ctx == NULL)

    {

      *errnop = errno;

      *h_errnop = NETDB_INTERNAL;

      return NSS_STATUS_UNAVAIL;

    }

  for (int i = 0; i < nqtypes; ++i)

    {

      int r = __res_context_query (ctx, name, ns_c_in, qtypes[i],

				   buf, sizeof (buf), &ansp.ptr, NULL, NULL,

				   NULL, NULL);

      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))

	    continue;

	  /* Number of answers.   */

	  unsigned int ancount = ntohs (ansp.buf->hdr.ancount);

	  /* 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)

	    {

	    unavail:

	      status = NSS_STATUS_UNAVAIL;

	      break;

	    }

	  /* Skip over the name and the two 16-bit values containing type

	     and class.  */

	  ptr += s + 2 * sizeof (uint16_t);

	  while (ancount-- > 0)

	    {

	      /* Now the reply.  First again the name from the query,

		 then type, class, TTL, and the length of the RDATA.

		 We remember the name start.  */

	      unsigned char *namestart = ptr;

	      s = __dn_skipname (ptr, endptr);

	      if (s < 0)

		goto unavail;

	      ptr += s;

	      /* Check that there are enough bytes for the RR

		 metadata.  */

	      if (endptr - ptr < 10)

		goto unavail;

	      /* Check whether type and class match.  */

	      uint_fast16_t type;

	      NS_GET16 (type, ptr);

	      if (type == qtypes[i])

		{

		  /* We found the record.  */

		  s = __dn_expand (ansp.buf->buf, endptr, namestart,

				   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;

		    }

		  goto out;

		}

	      if (type != ns_t_cname)

		goto unavail;

	      if (__ns_get16 (ptr) != ns_c_in)

		goto unavail;

	      /* Also skip over class and TTL.  */

	      ptr += sizeof (uint16_t) + sizeof (uint32_t);

	      /* Skip over RDATA length and RDATA itself.  */

	      uint16_t rdatalen = __ns_get16 (ptr);

	      ptr += sizeof (uint16_t);

	      /* Not enough room for RDATA.  */

	      if (endptr - ptr < rdatalen)

		goto unavail;

	      ptr += rdatalen;

	    }

	}

      /* Restore original buffer before retry.  */

      if (ansp.ptr != buf)

	{

	  free (ansp.ptr);

	  ansp.ptr = buf;

	}

    }

 out:

  *h_errnop = h_errno;

  if (ansp.ptr != buf)

    free (ansp.ptr);

  __resolv_context_put (ctx);

  return status;

}