1 /* Host name canonicalization 2 3 Copyright (C) 2005-2021 Free Software Foundation, Inc. 4 5 Written by Derek Price <derek@ximbiot.com>. 6 7 This file is free software: you can redistribute it and/or modify 8 it under the terms of the GNU Lesser General Public License as 9 published by the Free Software Foundation; either version 3 of the 10 License, or (at your option) any later version. 11 12 This file 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 Lesser General Public License for more details. 16 17 You should have received a copy of the GNU Lesser 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 * 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 56 <https://pubs.opengroup.org/onlinepubs/9699919799/functions/getaddrinfo.html>, 57 RFC 1034 <https://www.ietf.org/rfc/rfc1034.txt>, & RFC 2181 58 <https://www.ietf.org/rfc/rfc2181.txt> for more on what this confusing 59 term really refers to. */ 60 char * 61 canon_host_r (char const *host, int *cherror) /* */ 62 { 63 char *retval = NULL; 64 static struct addrinfo hints; 65 struct addrinfo *res = NULL; 66 int status; 67 68 hints.ai_flags = AI_CANONNAME; 69 status = getaddrinfo (host, NULL, &hints, &res); 70 if (!status) 71 { 72 /* https://lists.gnu.org/r/bug-coreutils/2006-09/msg00300.html 73 says Darwin 7.9.0 getaddrinfo returns 0 but sets 74 res->ai_canonname to NULL. */ 75 retval = strdup (res->ai_canonname ? res->ai_canonname : host); 76 if (!retval && cherror) 77 *cherror = EAI_MEMORY; 78 freeaddrinfo (res); 79 } 80 else if (cherror) 81 *cherror = status; 82 83 return retval; 84 } 85 86 /* Return a string describing the last error encountered by canon_host. */ 87 const char * 88 ch_strerror (void) /* */ 89 { 90 return gai_strerror (last_cherror); 91 }