Line data    Source code

       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 modify
       8             :    it under the terms of the GNU General Public License as published by
       9             :    the Free Software Foundation; either version 3, or (at your option)
      10             :    any later version.
      11             : 
      12             :    This program is distributed in the hope that it will be useful,
      13             :    but WITHOUT ANY WARRANTY; without even the implied warranty of
      14             :    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
      15             :    GNU 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, see <http://www.gnu.org/licenses/>.  */
      19             : 
      20             : #include <config.h>
      21             : 
      22             : #include "canon-host.h"
      23             : 
      24             : #include <string.h>
      25             : 
      26             : #include "getaddrinfo.h"
      27             : 
      28             : /* Store the last error for the single-threaded version of this function.  */
      29             : static int last_cherror;
      30             : 
      31             : /* Single-threaded of wrapper for canon_host_r.  After a NULL return, error
      32             :    messages may be retrieved via ch_strerror().  */
      33             : char *
      34           0 : canon_host (const char *host)
      35             : {
      36           0 :   return canon_host_r (host, &last_cherror);
      37             : }
      38             : 
      39             : /* Return a malloc'd string containing the canonical hostname associated with
      40             :    HOST, or NULL if a canonical name cannot be determined.  On NULL return,
      41             :    if CHERROR is not NULL, set *CHERROR to an error code as returned by
      42             :    getaddrinfo().  Use ch_strerror_r() or gai_strerror() to convert a *CHERROR
      43             :    value to a string suitable for error messages.
      44             : 
      45             :    WARNINGS
      46             :      HOST must be a string representation of a resolvable name for this host.
      47             :      Strings containing an IP address in dotted decimal notation will be
      48             :      returned as-is, without further resolution.
      49             : 
      50             :      The use of the word "canonical" in this context is unfortunate but
      51             :      entrenched.  The value returned by this function will be the end result
      52             :      of the resolution of any CNAME chains in the DNS.  There may only be one
      53             :      such value for any given hostname, though the actual IP address
      54             :      referenced by this value and the device using that IP address may each
      55             :      actually have any number of such "canonical" hostnames.  See the POSIX
      56             :      getaddrinfo spec <http://www.opengroup.org/susv3xsh/getaddrinfo.html">,
      57             :      RFC 1034 <http://www.faqs.org/rfcs/rfc1034.html>, & RFC 2181
      58             :      <http://www.faqs.org/rfcs/rfc2181.html> for more on what this confusing
      59             :      term really refers to. */
      60             : char *
      61           0 : canon_host_r (char const *host, int *cherror)
      62             : {
      63           0 :   char *retval = NULL;
      64             :   static struct addrinfo hints;
      65           0 :   struct addrinfo *res = NULL;
      66             :   int status;
      67             : 
      68           0 :   hints.ai_flags = AI_CANONNAME;
      69           0 :   status = getaddrinfo (host, NULL, &hints, &res);
      70           0 :   if (!status)
      71             :     {
      72             :       /* http://lists.gnu.org/archive/html/bug-coreutils/2006-09/msg00300.html
      73             :          says Darwin 7.9.0 getaddrinfo returns 0 but sets
      74             :          res->ai_canonname to NULL.  */
      75           0 :       retval = strdup (res->ai_canonname ? res->ai_canonname : host);
      76           0 :       if (!retval && cherror)
      77           0 :         *cherror = EAI_MEMORY;
      78           0 :       freeaddrinfo (res);
      79             :     }
      80           0 :   else if (cherror)
      81           0 :     *cherror = status;
      82             : 
      83           0 :   return retval;
      84             : }
      85             : 
      86             : /* Return a string describing the last error encountered by canon_host.  */
      87             : const char *
      88           0 : ch_strerror (void)
      89             : {
      90           0 :   return gai_strerror (last_cherror);
      91             : }