1 /* Host name canonicalization
2
3 Copyright (C) 2005-2018 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 <https://www.gnu.org/licenses/>. */
19
20 #include <config.h>
21
22 #include "canon-host.h"
23
24 #include <string.h>
25 #include <netdb.h>
26
27 /* Store the last error for the single-threaded version of this function. */
28 static int last_cherror;
29
30 /* Single-threaded of wrapper for canon_host_r. After a NULL return, error
31 messages may be retrieved via ch_strerror(). */
32 char *
canon_host(const char * host)33 canon_host (const char *host)
34 {
35 return canon_host_r (host, &last_cherror);
36 }
37
38 /* Return a malloc'd string containing the canonical hostname associated with
39 HOST, or NULL if a canonical name cannot be determined. On NULL return,
40 if CHERROR is not NULL, set *CHERROR to an error code as returned by
41 getaddrinfo(). Use ch_strerror_r() or gai_strerror() to convert a *CHERROR
42 value to a string suitable for error messages.
43
44 WARNINGS
45 HOST must be a string representation of a resolvable name for this host.
46 Strings containing an IP address in dotted decimal notation will be
47 returned as-is, without further resolution.
48
49 The use of the word "canonical" in this context is unfortunate but
50 entrenched. The value returned by this function will be the end result
51 of the resolution of any CNAME chains in the DNS. There may only be one
52 such value for any given hostname, though the actual IP address
53 referenced by this value and the device using that IP address may each
54 actually have any number of such "canonical" hostnames. See the POSIX
55 getaddrinfo spec <http://www.opengroup.org/susv3xsh/getaddrinfo.html">,
56 RFC 1034 <https://www.ietf.org/rfc/rfc1034.txt>, & RFC 2181
57 <https://www.ietf.org/rfc/rfc2181.txt> for more on what this confusing
58 term really refers to. */
59 char *
canon_host_r(char const * host,int * cherror)60 canon_host_r (char const *host, int *cherror)
61 {
62 char *retval = NULL;
63 static struct addrinfo hints;
64 struct addrinfo *res = NULL;
65 int status;
66
67 hints.ai_flags = AI_CANONNAME;
68 status = getaddrinfo (host, NULL, &hints, &res);
69 if (!status)
70 {
71 /* https://lists.gnu.org/r/bug-coreutils/2006-09/msg00300.html
72 says Darwin 7.9.0 getaddrinfo returns 0 but sets
73 res->ai_canonname to NULL. */
74 retval = strdup (res->ai_canonname ? res->ai_canonname : host);
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 *
ch_strerror(void)87 ch_strerror (void)
88 {
89 return gai_strerror (last_cherror);
90 }
91