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.
 */
 
 
#include <sys/types.h>
#include <stdlib.h>
#include <string.h>
#include "ares.h"
#include "ares_dns.h"
#include "ares_private.h"
 
#ifndef WIN32
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#ifndef __CYGWIN__
#  include "ares_nameser.h"
#endif
#include <netdb.h>
#endif
 
int ares_parse_a_reply(const unsigned char* abuf, int alen,
   struct hostent** host)
{
   unsigned int qdcount, ancount;
   int status, i, rr_type, rr_class, rr_len, naddrs;
   long int len;
   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 < (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)
      {
         free(rr_name);
         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 (aptr + rr_len > abuf + alen)
      {
         free(rr_name);
         status = ARES_EBADRESP;
         break;
      }
 
      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;
            if (!naddrs && addrs)
               free(addrs);
            *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;
}