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.  */
31static 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().  */
35char *
36canon_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. */
62char *
63canon_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.  */
86const char *
87ch_strerror (void)
88{
89  return gai_strerror (last_cherror);
90}
91