lib/canon-host.c

   1 /* Host name canonicalization
   2
   3    Copyright (C) 1995, 1999, 2000 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_STDLIB_H
  30 # include <stdlib.h>
  31 #endif
  32 #ifdef HAVE_STRING_H
  33 # include <string.h>
  34 #endif
  35 #ifdef HAVE_NETDB_H
  36 # include <netdb.h>
  37 #endif
  38 #ifdef HAVE_SYS_SOCKET_H
  39 # include <sys/socket.h>
  40 #endif
  41
  42 #ifdef HAVE_NETINET_IN_H
  43 # include <netinet/in.h>
  44 #endif
  45 #ifdef HAVE_ARPA_INET_H
  46 # include <arpa/inet.h>
  47 #endif
  48
  49 #ifndef strdup
  50 char *strdup ();
  51 #endif
  52
  53 /* Returns the canonical hostname associated with HOST (allocated in a static
  54    buffer), or 0 if it can't be determined.  */
  55 char *
  56 canon_host (const char *host)
  57 {
  58 #ifdef HAVE_GETHOSTBYNAME
  59   struct hostent *he = gethostbyname (host);
  60
  61   if (he)
  62     {
  63 # ifdef HAVE_GETHOSTBYADDR
  64       char *addr = 0;
  65
  66       /* Try and get an ascii version of the numeric host address.  */
  67       switch (he->h_addrtype)
  68         {
  69 #  ifdef HAVE_INET_NTOA
  70         case AF_INET:
  71           addr = inet_ntoa (*(struct in_addr *) he->h_addr);
  72           break;
  73 #  endif /* HAVE_INET_NTOA */
  74         }
  75
  76       if (addr && strcmp (he->h_name, addr) == 0)
  77         {
  78           /* gethostbyname has returned a string representation of the IP
  79              address, for example, "127.0.0.1".  So now, look up the host
  80              name via the address.  Although it may seem reasonable to look
  81              up the host name via the address, we must not pass `he->h_addr'
  82              directly to gethostbyaddr because on some systems he->h_addr
  83              is located in a static library buffer that is reused in the
  84              gethostbyaddr call.  Make a copy and use that instead.  */
  85           char *h_addr_copy = (char *) malloc (he->h_length);
  86           if (h_addr_copy == NULL)
  87             he = NULL;
  88           else
  89             {
  90               memcpy (h_addr_copy, he->h_addr, he->h_length);
  91               he = gethostbyaddr (h_addr_copy, he->h_length, he->h_addrtype);
  92               free (h_addr_copy);
  93             }
  94         }
  95 # endif /* HAVE_GETHOSTBYADDR */
  96
  97       if (he)
  98         return (char *) (he->h_name);
  99     }
 100 #endif /* HAVE_GETHOSTBYNAME */
 101   return 0;
 102 }
 103
 104 #ifdef TEST_CANON_HOST
 105 int
 106 main (int argc, char **argv)
 107 {
 108   int i;
 109   for (i = 1; i < argc; i++)
 110     {
 111       char *s = canon_host (argv[i]);
 112       printf ("%s: %s\n", argv[i], (s ? s : "<undef>"));
 113     }
 114   exit (0);
 115 }
 116 #endif /* TEST_CANON_HOST */