1: /* Host name canonicalization
    2: 
    3:    Copyright (C) 2005, 2006, 2007 Free Software Foundation, Inc.
    4: 
    5:    Written by Derek Price <derek@ximbiot.com>.
    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., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.  */
   20: 
   21: #include <config.h>
   22: 
   23: #include "canon-host.h"
   24: 
   25: #include <string.h>
   26: 
   27: #include "getaddrinfo.h"
   28: 
   29: /* Store the last error for the single-threaded version of this function.  */
   30: static int last_cherror;
   31: 
   32: /* Single-threaded of wrapper for canon_host_r.  After a NULL return, error
   33:    messages may be retrieved via ch_strerror().  */
   34: char *
   35: canon_host (const char *host)
   36: {
   37:   return canon_host_r (host, &last_cherror);
   38: }
   39: 
   40: /* Return a malloc'd string containing the canonical hostname associated with
   41:    HOST, or NULL if a canonical name cannot be determined.  On NULL return,
   42:    if CHERROR is not NULL, set *CHERROR to an error code as returned by
   43:    getaddrinfo().  Use ch_strerror_r() or gai_strerror() to convert a *CHERROR
   44:    value to a string suitable for error messages.
   45: 
   46:    WARNINGS
   47:      HOST must be a string representation of a resolvable name for this host.
   48:      Strings containing an IP address in dotted decimal notation will be
   49:      returned as-is, without further resolution.
   50: 
   51:      The use of the word "canonical" in this context is unfortunate but
   52:      entrenched.  The value returned by this function will be the end result
   53:      of the resolution of any CNAME chains in the DNS.  There may only be one
   54:      such value for any given hostname, though the actual IP address
   55:      referenced by this value and the device using that IP address may each
   56:      actually have any number of such "canonical" hostnames.  See the POSIX
   57:      getaddrinfo spec <http://www.opengroup.org/susv3xsh/getaddrinfo.html">,
   58:      RFC 1034 <http://www.faqs.org/rfcs/rfc1034.html>, & RFC 2181
   59:      <http://www.faqs.org/rfcs/rfc2181.html> for more on what this confusing
   60:      term really refers to. */
   61: char *
   62: canon_host_r (char const *host, int *cherror)
   63: {
   64:   char *retval = NULL;
   65:   static struct addrinfo hints;
   66:   struct addrinfo *res = NULL;
   67:   int status;
   68: 
   69:   hints.ai_flags = AI_CANONNAME;
   70:   status = getaddrinfo (host, NULL, &hints, &res);
   71:   if (!status)
   72:     {
   73:       /* http://lists.gnu.org/archive/html/bug-coreutils/2006-09/msg00300.html
   74:          says Darwin 7.9.0 getaddrinfo returns 0 but sets
   75:          res->ai_canonname to NULL.  */
   76:       retval = strdup (res->ai_canonname ? res->ai_canonname : host);
   77:       if (!retval && cherror)
   78:         *cherror = EAI_MEMORY;
   79:       freeaddrinfo (res);
   80:     }
   81:   else if (cherror)
   82:     *cherror = status;
   83: 
   84:   return retval;
   85: }
   86: 
   87: /* Return a string describing the last error encountered by canon_host.  */
   88: const char *
   89: ch_strerror (void)
   90: {
   91:   return gai_strerror (last_cherror);
   92: }