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/* Host name canonicalization
Copyright (C) 1995, 1999 Free Software Foundation, Inc.
Written by Miles Bader <miles@gnu.ai.mit.edu>
This program is free software; you can redistribute it and/or
modify it under the terms of the GNU General Public License as
published by the Free Software Foundation; either version 2, or (at
your option) any later version.
This program is distributed in the hope that it will be useful, but
WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
General Public License for more details.
You should have received a copy of the GNU General Public License
along with this program; if not, write to the Free Software Foundation,
Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA. */
#ifdef HAVE_CONFIG_H
# include <config.h>
#endif
#include <sys/types.h>
#ifdef HAVE_UNISTD_H
# include <unistd.h>
#endif
#ifdef HAVE_STRING_H
# include <string.h>
#endif
#ifdef HAVE_NETDB_H
# include <netdb.h>
#endif
#ifdef HAVE_SYS_SOCKET_H
# include <sys/socket.h>
#endif
#ifdef HAVE_NETINET_IN_H
# include <netinet/in.h>
#endif
#ifdef HAVE_ARPA_INET_H
# include <arpa/inet.h>
#endif
void free ();
/* Returns the canonical hostname associated with HOST (allocated in a static
buffer), or 0 if it can't be determined. */
char *
canon_host (const char *host)
{
#ifdef HAVE_GETHOSTBYNAME
struct hostent *he = gethostbyname (host);
if (he)
{
# ifdef HAVE_GETHOSTBYADDR
char *addr = 0;
/* Try and get an ascii version of the numeric host address. */
switch (he->h_addrtype)
{
# ifdef HAVE_INET_NTOA
case AF_INET:
addr = inet_ntoa (*(struct in_addr *) he->h_addr);
break;
# endif /* HAVE_INET_NTOA */
}
if (addr && strcmp (he->h_name, addr) == 0)
{
/* gethostbyname has returned a string representation of the IP
address, for example, "127.0.0.1". So now, look up the host
name via the address. Although it may seem reasonable to look
up the host name via the address, we must not pass `he->h_addr'
directly to gethostbyaddr because on some systems he->h_addr
is located in a static library buffer that is reused in the
gethostbyaddr call. Make a copy and use that instead. */
char *h_addr_copy = strdup (he->h_addr);
if (h_addr_copy == NULL)
he = NULL;
else
{
he = gethostbyaddr (h_addr_copy, he->h_length, he->h_addrtype);
free (h_addr_copy);
}
}
# endif /* HAVE_GETHOSTBYADDR */
if (he)
return (char *) (he->h_name);
}
#endif /* HAVE_GETHOSTBYNAME */
return 0;
}
#ifdef TEST_CANON_HOST
int
main (int argc, char **argv)
{
int i;
for (i = 1; i < argc; i++)
{
char *s = canon_host (argv[i]);
printf ("%s: %s\n", argv[i], (s ? s : "<undef>"));
}
exit (0);
}
#endif /* TEST_CANON_HOST */
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