c-ares/ares_parse_ptr_reply.c

/* Copyright 1998 by the Massachusetts Institute of Technology.
 *
 * Permission to use, copy, modify, and distribute this
 * software and its documentation for any purpose and without
 * fee is hereby granted, provided that the above copyright
 * notice appear in all copies and that both that copyright
 * notice and this permission notice appear in supporting
 * documentation, and that the name of M.I.T. not be used in
 * advertising or publicity pertaining to distribution of the
 * software without specific, written prior permission.
 * M.I.T. makes no representations about the suitability of
 * this software for any purpose.  It is provided "as is"
 * without express or implied warranty.
 */

#include "setup.h"
#include <sys/types.h>

#if defined(WIN32) && !defined(WATT32)
#include "nameser.h"
#else
#include <sys/socket.h>
#include <netinet/in.h>
#include <netdb.h>
#include <arpa/nameser.h>
#endif

#include <stdlib.h>
#include <string.h>
#include "ares.h"
#include "ares_dns.h"
#include "ares_private.h"

int ares_parse_ptr_reply(const unsigned char *abuf, int alen, const void *addr,
                         int addrlen, int family, struct hostent **host)
{
  unsigned int qdcount, ancount;
  int status, i, rr_type, rr_class, rr_len;
  long len;
  const unsigned char *aptr;
  char *ptrname, *hostname, *rr_name, *rr_data;
  struct hostent *hostent;

  /* Set *host to NULL for all failure cases. */
  *host = NULL;

  /* Give up if abuf doesn't have room for a header. */
  if (alen < HFIXEDSZ)
    return ARES_EBADRESP;

  /* Fetch the question and answer count from the header. */
  qdcount = DNS_HEADER_QDCOUNT(abuf);
  ancount = DNS_HEADER_ANCOUNT(abuf);
  if (qdcount != 1)
    return ARES_EBADRESP;

  /* Expand the name from the question, and skip past the question. */
  aptr = abuf + HFIXEDSZ;
  status = ares_expand_name(aptr, abuf, alen, &ptrname, &len);
  if (status != ARES_SUCCESS)
    return status;
  if (aptr + len + QFIXEDSZ > abuf + alen)
    {
      free(ptrname);
      return ARES_EBADRESP;
    }
  aptr += len + QFIXEDSZ;

  /* Examine each answer resource record (RR) in turn. */
  hostname = NULL;
  for (i = 0; i < (int)ancount; i++)
    {
      /* Decode the RR up to the data field. */
      status = ares_expand_name(aptr, abuf, alen, &rr_name, &len);
      if (status != ARES_SUCCESS)
        break;
      aptr += len;
      if (aptr + RRFIXEDSZ > abuf + alen)
        {
          status = ARES_EBADRESP;
          break;
        }
      rr_type = DNS_RR_TYPE(aptr);
      rr_class = DNS_RR_CLASS(aptr);
      rr_len = DNS_RR_LEN(aptr);
      aptr += RRFIXEDSZ;

      if (rr_class == C_IN && rr_type == T_PTR
          && strcasecmp(rr_name, ptrname) == 0)
        {
          /* Decode the RR data and set hostname to it. */
          status = ares_expand_name(aptr, abuf, alen, &rr_data, &len);
          if (status != ARES_SUCCESS)
            break;
          if (hostname)
            free(hostname);
          hostname = rr_data;
        }

      if (rr_class == C_IN && rr_type == T_CNAME)
        {
          /* Decode the RR data and replace ptrname with it. */
          status = ares_expand_name(aptr, abuf, alen, &rr_data, &len);
          if (status != ARES_SUCCESS)
            break;
          free(ptrname);
          ptrname = rr_data;
        }

      free(rr_name);
      aptr += rr_len;
      if (aptr > abuf + alen)
        {
          status = ARES_EBADRESP;
          break;
        }
    }

  if (status == ARES_SUCCESS && !hostname)
    status = ARES_ENODATA;
  if (status == ARES_SUCCESS)
    {
      /* We got our answer.  Allocate memory to build the host entry. */
      hostent = malloc(sizeof(struct hostent));
      if (hostent)
        {
          hostent->h_addr_list = malloc(2 * sizeof(char *));
          if (hostent->h_addr_list)
            {
              hostent->h_addr_list[0] = malloc(addrlen);
              if (hostent->h_addr_list[0])
                {
                  hostent->h_aliases = malloc(sizeof (char *));
                  if (hostent->h_aliases)
                    {
                      /* Fill in the hostent and return successfully. */
                      hostent->h_name = hostname;
                      hostent->h_aliases[0] = NULL;
                      hostent->h_addrtype = family;
                      hostent->h_length = addrlen;
                      memcpy(hostent->h_addr_list[0], addr, addrlen);
                      hostent->h_addr_list[1] = NULL;
                      *host = hostent;
                      free(ptrname);
                      return ARES_SUCCESS;
                    }
                  free(hostent->h_addr_list[0]);
                }
              free(hostent->h_addr_list);
            }
          free(hostent);
        }
      status = ARES_ENOMEM;
    }
  if (hostname)
    free(hostname);
  free(ptrname);
  return status;
}