ares_parse_a_reply.c

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/* 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.
 *
 * CHANGELOG: this file has been modified by Sergio Perez Alcañiz <serpeal@disca.upv.es> 
 *            Departamento de Informática de Sistemas y Computadores          
 *            Universidad Politécnica de Valencia                             
 *            Valencia (Spain)    
 *            Date: April 2003                                          
 *
 */

#include "ares_private.h"
#include "ares_dns.h"

int ares_parse_a_reply(const unsigned char *abuf, int alen,
                       struct hostent **host)
{
  unsigned int qdcount, ancount;
  int status, i, len, rr_type, rr_class, rr_len, naddrs;
  int naliases;
  const unsigned char *aptr;
  char *hostname, *rr_name, *rr_data, **aliases;
  struct in_addr *addrs;
  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, &hostname, &len);
  if (status != ARES_SUCCESS)
    return status;
  if (aptr + len + QFIXEDSZ > abuf + alen)
    {
      free(hostname);
      return ARES_EBADRESP;
    }
  aptr += len + QFIXEDSZ;

  /* Allocate addresses and aliases; ancount gives an upper bound for both. */
  addrs = malloc(ancount * sizeof(struct in_addr));
  if (!addrs)
    {
      free(hostname);
      return ARES_ENOMEM;
    }
  aliases = malloc((ancount + 1) * sizeof(char *));
  if (!aliases)
    {
      free(hostname);
      free(addrs);
      return ARES_ENOMEM;
    }
  naddrs = 0;
  naliases = 0;

  /* Examine each answer resource record (RR) in turn. */
  for (i = 0; i < 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_A
          && rr_len == sizeof(struct in_addr)
          && strcasecmp(rr_name, hostname) == 0)
        {
          memcpy(&addrs[naddrs], aptr, sizeof(struct in_addr));
          naddrs++;
          status = ARES_SUCCESS;
        }

      if (rr_class == C_IN && rr_type == T_CNAME)
        {
          /* Record the RR name as an alias. */
          aliases[naliases] = rr_name;
          naliases++;

          /* Decode the RR data and replace the hostname with it. */
          status = ares_expand_name(aptr, abuf, alen, &rr_data, &len);
          if (status != ARES_SUCCESS)
            break;
          free(hostname);
          hostname = rr_data;
        }
      else
        free(rr_name);

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

  if (status == ARES_SUCCESS && naddrs == 0)
    status = ARES_ENODATA;
  if (status == ARES_SUCCESS)
    {
      /* We got our answer.  Allocate memory to build the host entry. */
      aliases[naliases] = NULL;
      hostent = malloc(sizeof(struct hostent));
      if (hostent)
        {
          hostent->h_addr_list = malloc((naddrs + 1) * sizeof(char *));
          if (hostent->h_addr_list)
            {
              /* Fill in the hostent and return successfully. */
              hostent->h_name = hostname;
              hostent->h_aliases = aliases;
              hostent->h_addrtype = AF_INET;
              hostent->h_length = sizeof(struct in_addr);
              for (i = 0; i < naddrs; i++)
                hostent->h_addr_list[i] = (char *) &addrs[i];
              hostent->h_addr_list[naddrs] = NULL;
              *host = hostent;
              return ARES_SUCCESS;
            }
          free(hostent);
        }
      status = ARES_ENOMEM;
    }
  for (i = 0; i < naliases; i++)
    free(aliases[i]);
  free(aliases);
  free(addrs);
  free(hostname);
  return status;
}

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