lib/canon-host.c

   1 /* Host name canonicalization
   2
   3    Copyright (C) 1995, 1999 Free Software Foundation, Inc.
   4
   5    Written by Miles Bader <miles@gnu.ai.mit.edu>
   6
   7    This program is free software; you can redistribute it and/or
   8    modify it under the terms of the GNU General Public License as
   9    published by the Free Software Foundation; either version 2, or (at
  10    your option) any later version.
  11
  12    This program is distributed in the hope that it will be useful, but
  13    WITHOUT ANY WARRANTY; without even the implied warranty of
  14    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  15    General Public License for more details.
  16
  17    You should have received a copy of the GNU General Public License
  18    along with this program; if not, write to the Free Software Foundation,
  19    Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.  */
  20
  21 #ifdef HAVE_CONFIG_H
  22 # include <config.h>
  23 #endif
  24
  25 #include <sys/types.h>
  26 #ifdef HAVE_UNISTD_H
  27 # include <unistd.h>
  28 #endif
  29 #ifdef HAVE_STRING_H
  30 # include <string.h>
  31 #endif
  32 #ifdef HAVE_NETDB_H
  33 # include <netdb.h>
  34 #endif
  35 #ifdef HAVE_SYS_SOCKET_H
  36 # include <sys/socket.h>
  37 #endif
  38
  39 #ifdef HAVE_NETINET_IN_H
  40 # include <netinet/in.h>
  41 #endif
  42 #ifdef HAVE_ARPA_INET_H
  43 # include <arpa/inet.h>
  44 #endif
  45
  46 void free ();
  47
  48 /* Returns the canonical hostname associated with HOST (allocated in a static
  49    buffer), or 0 if it can't be determined.  */
  50 char *
  51 canon_host (const char *host)
  52 {
  53 #ifdef HAVE_GETHOSTBYNAME
  54   struct hostent *he = gethostbyname (host);
  55
  56   if (he)
  57     {
  58 # ifdef HAVE_GETHOSTBYADDR
  59       char *addr = 0;
  60
  61       /* Try and get an ascii version of the numeric host address.  */
  62       switch (he->h_addrtype)
  63         {
  64 #  ifdef HAVE_INET_NTOA
  65         case AF_INET:
  66           addr = inet_ntoa (*(struct in_addr *) he->h_addr);
  67           break;
  68 #  endif /* HAVE_INET_NTOA */
  69         }
  70
  71       if (addr && strcmp (he->h_name, addr) == 0)
  72         {
  73           /* gethostbyname has returned a string representation of the IP
  74              address, for example, "127.0.0.1".  So now, look up the host
  75              name via the address.  Although it may seem reasonable to look
  76              up the host name via the address, we must not pass `he->h_addr'
  77              directly to gethostbyaddr because on some systems he->h_addr
  78              is located in a static library buffer that is reused in the
  79              gethostbyaddr call.  Make a copy and use that instead.  */
  80           char *h_addr_copy = strdup (he->h_addr);
  81           if (h_addr_copy == NULL)
  82             he = NULL;
  83           else
  84             {
  85               he = gethostbyaddr (h_addr_copy, he->h_length, he->h_addrtype);
  86               free (h_addr_copy);
  87             }
  88         }
  89 # endif /* HAVE_GETHOSTBYADDR */
  90
  91       if (he)
  92         return (char *) (he->h_name);
  93     }
  94 #endif /* HAVE_GETHOSTBYNAME */
  95   return 0;
  96 }
  97
  98 #ifdef TEST_CANON_HOST
  99 int
 100 main (int argc, char **argv)
 101 {
 102   int i;
 103   for (i = 1; i < argc; i++)
 104     {
 105       char *s = canon_host (argv[i]);
 106       printf ("%s: %s\n", argv[i], (s ? s : "<undef>"));
 107     }
 108   exit (0);
 109 }
 110 #endif /* TEST_CANON_HOST */