lib/canon-host.c

   1 /* Host name canonicalization
   2
   3    Copyright (C) 1995 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 /* Returns the canonical hostname associated with HOST (allocated in a static
  47    buffer), or 0 if it can't be determined.  */
  48 char *
  49 canon_host (host)
  50      char *host;
  51 {
  52 #ifdef HAVE_GETHOSTBYNAME
  53   struct hostent *he = gethostbyname (host);
  54
  55   if (he)
  56     {
  57 # ifdef HAVE_GETHOSTBYADDR
  58       char *addr = 0;
  59
  60       /* Try and get an ascii version of the numeric host address.  */
  61       switch (he->h_addrtype)
  62         {
  63 #  ifdef HAVE_INET_NTOA
  64         case AF_INET:
  65           addr = inet_ntoa (*(struct in_addr *) he->h_addr);
  66           break;
  67 #  endif /* HAVE_INET_NTOA */
  68         }
  69
  70       if (addr && strcmp (he->h_name, addr) == 0)
  71         /* gethostbyname() cheated!  Lookup the host name via the address
  72            this time to get the actual host name.  */
  73         he = gethostbyaddr (he->h_addr, he->h_length, he->h_addrtype);
  74 # endif /* HAVE_GETHOSTBYADDR */
  75
  76       if (he)
  77         return (char *) (he->h_name);
  78     }
  79 #endif /* HAVE_GETHOSTBYNAME */
  80   return 0;
  81 }