external/gpl2/xcvs/dist/lib/canon-host.c

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