ares_gethostbyaddr.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 <stdio.h>
#include <stdlib.h>
#include <string.h>
 
#ifndef WIN32
#include <sys/socket.h>
#include <netinet/in.h>
#ifndef __CYGWIN__
#  include "ares_nameser.h"
#endif
#include <netdb.h>
#endif
 
#include "ares.h"
#include "ares_private.h"
 
struct addr_query {
  /* Arguments passed to ares_gethostbyaddr() */
  ares_channel channel;
  struct in_addr addr;
  ares_host_callback callback;
  void *arg;
 
  const char *remaining_lookups;
};
 
static void next_lookup(struct addr_query *aquery);
static void addr_callback(void *arg, int status, unsigned char *abuf,
              int alen);
static void end_aquery(struct addr_query *aquery, int status,
               struct hostent *host);
static int file_lookup(struct in_addr *addr, struct hostent **host);
 
#ifdef WIN32
extern char w32hostspath[];
#endif
 
void ares_gethostbyaddr(ares_channel channel, const void *addr, int addrlen,
            int family, ares_host_callback callback, void *arg)
{
  struct addr_query *aquery;
 
  if (family != AF_INET || addrlen != sizeof(struct in_addr))
    {
      callback(arg, ARES_ENOTIMP, NULL);
      return;
    }
 
  aquery = malloc(sizeof(struct addr_query));
  if (!aquery)
    {
      callback(arg, ARES_ENOMEM, NULL);
      return;
    }
  aquery->channel = channel;
  memcpy(&aquery->addr, addr, sizeof(aquery->addr));
  aquery->callback = callback;
  aquery->arg = arg;
  aquery->remaining_lookups = channel->lookups;
 
  next_lookup(aquery);
}
 
static void next_lookup(struct addr_query *aquery)
{
  const char *p;
  char name[64];
  int a1, a2, a3, a4, status;
  struct hostent *host;
  unsigned long addr;
 
  for (p = aquery->remaining_lookups; *p; p++)
    {
      switch (*p)
    {
    case 'b':
      addr = ntohl(aquery->addr.s_addr);
      a1 = (addr >> 24) & 0xff; // .kw. in case signed-ness changes
      a2 = (addr >> 16) & 0xff;
      a3 = (addr >> 8) & 0xff;
      a4 = addr & 0xff;
      snprintf(name, sizeof(name), "%d.%d.%d.%d.in-addr.arpa", a4, a3, a2, a1);
      aquery->remaining_lookups = p + 1;
      ares_query(aquery->channel, name, C_IN, T_PTR, addr_callback,
             aquery);
      return;
    case 'f':
      status = file_lookup(&aquery->addr, &host);
      if (status != ARES_ENOTFOUND)
        {
          end_aquery(aquery, status, host);
          return;
        }
      break;
    }
    }
  end_aquery(aquery, ARES_ENOTFOUND, NULL);
}
 
static void addr_callback(void *arg, int status, unsigned char *abuf, int alen)
{
  struct addr_query *aquery = (struct addr_query *) arg;
  struct hostent *host;
 
  if (status == ARES_SUCCESS)
    {
      status = ares_parse_ptr_reply(abuf, alen, &aquery->addr,
                    sizeof(struct in_addr), AF_INET, &host);
      end_aquery(aquery, status, host);
    }
  else if (status == ARES_EDESTRUCTION)
    end_aquery(aquery, status, NULL);
  else
    next_lookup(aquery);
}
 
static void end_aquery(struct addr_query *aquery, int status,
               struct hostent *host)
{
  aquery->callback(aquery->arg, status, host);
  if (host)
    ares_free_hostent(host);
  free(aquery);
}
 
static int file_lookup(struct in_addr* addr, struct hostent** host)
{
   FILE* fp;
   int status;
 
#ifdef WIN32
   fopen_s(&fp, w32hostspath, "r");
#else
   fp = fopen(PATH_HOSTS, "r");
#endif
   if (!fp)
      return ARES_ENOTFOUND;
 
   while ((status = ares__get_hostent(fp, host)) == ARES_SUCCESS)
   {
      if (memcmp((*host)->h_addr, addr, sizeof(struct in_addr)) == 0)
         break;
      ares_free_hostent(*host);
   }
   fclose(fp);
   if (status == ARES_EOF)
      status = ARES_ENOTFOUND;
   if (status != ARES_SUCCESS)
      *host = NULL;
   return status;
}