1 /* Host name canonicalization
3 Copyright (C) 2005, 2006, 2007 Free Software Foundation, Inc.
5 Written by Derek Price <derek@ximbiot.com>.
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.
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.
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. */
23 #include "canon-host.h"
27 #include "getaddrinfo.h"
29 /* Store the last error for the single-threaded version of this function. */
30 static int last_cherror;
32 /* Single-threaded of wrapper for canon_host_r. After a NULL return, error
33 messages may be retrieved via ch_strerror(). */
35 canon_host (const char *host)
37 return canon_host_r (host, &last_cherror);
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.
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.
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. */
62 canon_host_r (char const *host, int *cherror)
65 static struct addrinfo hints;
66 struct addrinfo *res = NULL;
69 hints.ai_flags = AI_CANONNAME;
70 status = getaddrinfo (host, NULL, &hints, &res);
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;
87 /* Return a string describing the last error encountered by canon_host. */
91 return gai_strerror (last_cherror);