/* Host name canonicalization Copyright (C) 1995, 1999 Free Software Foundation, Inc. Written by Miles Bader 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 #endif #include #ifdef HAVE_UNISTD_H # include #endif #ifdef HAVE_STRING_H # include #endif #ifdef HAVE_NETDB_H # include #endif #ifdef HAVE_SYS_SOCKET_H # include #endif #ifdef HAVE_NETINET_IN_H # include #endif #ifdef HAVE_ARPA_INET_H # include #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 : "")); } exit (0); } #endif /* TEST_CANON_HOST */