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 } 91