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
  19    Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.  */
  20
  21 #ifdef HAVE_CONFIG_H
  22 #include <config.h>
  23 #endif
  24
  25 #ifdef HAVE_UNISTD_H
  26 #include <unistd.h>
  27 #endif
  28 #ifdef HAVE_STRING_H
  29 #include <string.h>
  30 #endif
  31 #ifdef HAVE_NETDB_H
  32 #include <netdb.h>
  33 #endif
  34 #ifdef HAVE_SYS_SOCKET_H
  35 #include <sys/socket.h>
  36 #endif
  37
  38 #ifdef HAVE_NETINET_IN_H
  39 #include <netinet/in.h>
  40 #endif
  41 #ifdef HAVE_ARPA_INET_H
  42 #include <arpa/inet.h>
  43 #endif
  44
  45 /* Returns the canonical hostname associated with HOST (allocated in a static
  46    buffer), or 0 if it can't be determined.  */
  47 char *
  48 canon_host (host)
  49      char *host;
  50 {
  51 #ifdef HAVE_GETHOSTBYNAME
  52   struct hostent *he = gethostbyname (host);
  53
  54   if (he)
  55     {
  56 #ifdef HAVE_GETHOSTBYADDR
  57       char *addr = 0;
  58
  59       /* Try and get an ascii version of the numeric host address.  */
  60       switch (he->h_addrtype)
  61         {
  62 #ifdef HAVE_INET_NTOA
  63         case AF_INET:
  64           addr = inet_ntoa (*(struct in_addr *) he->h_addr);
  65           break;
  66 #endif /* HAVE_INET_NTOA */
  67         }
  68
  69       if (addr && strcmp (he->h_name, addr) == 0)
  70         /* gethostbyname() cheated!  Lookup the host name via the address
  71            this time to get the actual host name.  */
  72         he = gethostbyaddr (he->h_addr, he->h_length, he->h_addrtype);
  73 #endif /* HAVE_GETHOSTBYADDR */
  74
  75       if (he)
  76         return (char *) (he->h_name);
  77     }
  78 #endif /* HAVE_GETHOSTBYNAME */
  79   return 0;
  80 }