ares_gethostbyname.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>
#include <ctype.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
 
#include "ares.h"
#include "ares_private.h"
#include "ares_local.h"
 
struct host_query {
  /* Arguments passed to ares_gethostbyname() */
  ares_channel channel;
  char *name;
  ares_host_callback callback;
  void *arg;
 
  const char *remaining_lookups;
};
 
static void next_lookup(struct host_query *hquery);
static void host_callback(void *arg, int status, unsigned char *abuf,
              int alen);
static void end_hquery(struct host_query *hquery, int status,
               struct hostent *host);
static int fake_hostent(const char *name, ares_host_callback callback,
            void *arg);
static int file_lookup(const char *name, struct hostent **host);
static void sort_addresses(struct hostent *host, struct apattern *sortlist,
               int nsort);
static int get_address_index(struct in_addr *addr, struct apattern *sortlist,
                 int nsort);
 
#ifdef WIN32
extern char w32hostspath[];
#endif
 
void ares_gethostbyname(ares_channel channel, const char* name, int family,
   ares_host_callback callback, void* arg)
{
   struct host_query* hquery;
 
   /* See if request can be handled by local pseudo-domain DNS */
   if (ares_local_gethostbyname(channel, name, family, callback, arg))
   {
      return;
   }
 
   /* Right now we only know how to look up Internet addresses. */
   if (family != AF_INET)
   {
      callback(arg, ARES_ENOTIMP, NULL);
      return;
   }
 
   if (fake_hostent(name, callback, arg))
      return;
 
   /* Allocate and fill in the host query structure. */
   hquery = malloc(sizeof(struct host_query));
   if (!hquery)
   {
      callback(arg, ARES_ENOMEM, NULL);
      return;
   }
   hquery->channel = channel;
   hquery->name = strdup(name);
   if (!hquery->name)
   {
      free(hquery);
      callback(arg, ARES_ENOMEM, NULL);
      return;
   }
   hquery->callback = callback;
   hquery->arg = arg;
   hquery->remaining_lookups = channel->lookups;
 
   /* Start performing lookups according to channel->lookups. */
   next_lookup(hquery);
}
 
static void next_lookup(struct host_query* hquery)
{
   int status;
   const char* p;
   struct hostent* host;
 
   for (p = hquery->remaining_lookups; *p; p++)
   {
      switch (*p)
      {
      case 'b':
         /* DNS lookup */
         hquery->remaining_lookups = p + 1;
         ares_search(hquery->channel, hquery->name, C_IN, T_A, host_callback,
            hquery);
         return;
 
      case 'f':
         /* Host file lookup */
         status = file_lookup(hquery->name, &host);
         if (status != ARES_ENOTFOUND)
         {
            end_hquery(hquery, status, host);
            return;
         }
         break;
      }
   }
   end_hquery(hquery, ARES_ENOTFOUND, NULL);
}
 
static void host_callback(void* arg, int status, unsigned char* abuf, int alen)
{
   struct host_query* hquery = (struct host_query*)arg;
   ares_channel channel = hquery->channel;
   struct hostent* host;
 
   if (status == ARES_SUCCESS)
   {
      status = ares_parse_a_reply(abuf, alen, &host);
      if (host && channel->nsort)
         sort_addresses(host, channel->sortlist, channel->nsort);
      end_hquery(hquery, status, host);
   }
   else if (status == ARES_EDESTRUCTION)
      end_hquery(hquery, status, NULL);
   else
      next_lookup(hquery);
}
 
static void end_hquery(struct host_query* hquery, int status,
   struct hostent* host)
{
   hquery->callback(hquery->arg, status, host);
   if (host)
      ares_free_hostent(host);
   free(hquery->name);
   free(hquery);
}
 
/* If the name looks like an IP address, fake up a host entry, end the
 * query immediately, and return true.  Otherwise return false.
 */
static int fake_hostent(const char* name, ares_host_callback callback,
   void* arg)
{
   struct in_addr addr;
   struct hostent hostent;
   const char* p;
   char* aliases[1] = { NULL };
   char* addrs[2];
 
   /* It only looks like an IP address if it's all numbers and dots. */
   for (p = name; *p; p++)
   {
      if (!isdigit((unsigned char)*p) && *p != '.')
         return 0;
   }
 
   /* It also only looks like an IP address if it's non-zero-length and
    * doesn't end with a dot.
    */
   if (p == name || *(p - 1) == '.')
      return 0;
 
   /* It looks like an IP address.  Figure out what IP address it is. */
#if defined(_MSC_VER) && _MSC_VER >= 1800  /* removing compilation warning in VS2013+ */
   inet_pton(AF_INET, name, &addr.s_addr);
#else
   addr.s_addr = inet_addr(name);
#endif
 
   if (addr.s_addr == INADDR_NONE)
   {
      callback(arg, ARES_EBADNAME, NULL);
      return 1;
   }
 
   /* Duplicate the name, to avoid a constness violation. */
   hostent.h_name = strdup(name);
   if (!hostent.h_name)
   {
      callback(arg, ARES_ENOMEM, NULL);
      return 1;
   }
 
   /* Fill in the rest of the host structure and terminate the query. */
   addrs[0] = (char*)&addr;
   addrs[1] = NULL;
   hostent.h_aliases = aliases;
   hostent.h_addrtype = AF_INET;
   hostent.h_length = sizeof(struct in_addr);
   hostent.h_addr_list = addrs;
   callback(arg, ARES_SUCCESS, &hostent);
 
   free(hostent.h_name);
   return 1;
}
 
int hostfile_lookup(const char* name, struct hostent** host)
{
   return file_lookup(name, host);
}
 
static int file_lookup(const char* name, struct hostent** host)
{
   FILE* fp;
   char** alias;
   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 (strcasecmp((*host)->h_name, name) == 0)
         break;
      for (alias = (*host)->h_aliases; *alias; alias++)
      {
         if (strcasecmp(*alias, name) == 0)
            break;
      }
      if (*alias)
         break;
      ares_free_hostent(*host);
   }
   fclose(fp);
   if (status == ARES_EOF)
      status = ARES_ENOTFOUND;
   if (status != ARES_SUCCESS)
      *host = NULL;
   return status;
}
 
static void sort_addresses(struct hostent* host, struct apattern* sortlist,
   int nsort)
{
   struct in_addr a1, a2;
   int i1, i2, ind1, ind2;
 
   /* This is a simple insertion sort, not optimized at all.  i1 walks
    * through the address list, with the loop invariant that everything
    * to the left of i1 is sorted.  In the loop body, the value at i1 is moved
    * back through the list (via i2) until it is in sorted order.
    */
   for (i1 = 0; host->h_addr_list[i1]; i1++)
   {
      memcpy(&a1, host->h_addr_list[i1], sizeof(struct in_addr));
      ind1 = get_address_index(&a1, sortlist, nsort);
      for (i2 = i1 - 1; i2 >= 0; i2--)
      {
         memcpy(&a2, host->h_addr_list[i2], sizeof(struct in_addr));
         ind2 = get_address_index(&a2, sortlist, nsort);
         if (ind2 <= ind1)
            break;
         memcpy(host->h_addr_list[i2 + 1], &a2, sizeof(struct in_addr));
      }
      memcpy(host->h_addr_list[i2 + 1], &a1, sizeof(struct in_addr));
   }
}
 
/* Find the first entry in sortlist which matches addr.  Return nsort
 * if none of them match.
 */
static int get_address_index(struct in_addr* addr, struct apattern* sortlist,
   int nsort)
{
   int i;
 
   for (i = 0; i < nsort; i++)
   {
      if ((addr->s_addr & sortlist[i].mask.s_addr) == sortlist[i].addr.s_addr)
         break;
   }
   return i;
}