92 lines
3.2 KiB
C
92 lines
3.2 KiB
C
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/* Host name canonicalization
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Copyright (C) 2005-2020 Free Software Foundation, Inc.
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Written by Derek Price <derek@ximbiot.com>.
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This program is free software: you can redistribute it and/or modify
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it under the terms of the GNU General Public License as published by
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the Free Software Foundation; either version 3, or (at your option)
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any later version.
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This program is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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GNU General Public License for more details.
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You should have received a copy of the GNU General Public License
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along with this program. If not, see <https://www.gnu.org/licenses/>. */
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#include <config.h>
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#include "canon-host.h"
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#include <string.h>
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#include <netdb.h>
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/* Store the last error for the single-threaded version of this function. */
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static int last_cherror;
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/* Single-threaded of wrapper for canon_host_r. After a NULL return, error
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messages may be retrieved via ch_strerror(). */
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char *
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canon_host (const char *host)
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{
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return canon_host_r (host, &last_cherror);
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}
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/* Return a malloc'd string containing the canonical hostname associated with
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HOST, or NULL if a canonical name cannot be determined. On NULL return,
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if CHERROR is not NULL, set *CHERROR to an error code as returned by
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getaddrinfo(). Use ch_strerror_r() or gai_strerror() to convert a *CHERROR
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value to a string suitable for error messages.
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WARNINGS
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HOST must be a string representation of a resolvable name for this host.
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Strings containing an IP address in dotted decimal notation will be
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returned as-is, without further resolution.
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The use of the word "canonical" in this context is unfortunate but
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entrenched. The value returned by this function will be the end result
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of the resolution of any CNAME chains in the DNS. There may only be one
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such value for any given hostname, though the actual IP address
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referenced by this value and the device using that IP address may each
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actually have any number of such "canonical" hostnames. See the POSIX
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getaddrinfo spec
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<https://pubs.opengroup.org/onlinepubs/9699919799/functions/getaddrinfo.html>,
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RFC 1034 <https://www.ietf.org/rfc/rfc1034.txt>, & RFC 2181
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<https://www.ietf.org/rfc/rfc2181.txt> for more on what this confusing
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term really refers to. */
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char *
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canon_host_r (char const *host, int *cherror)
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{
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char *retval = NULL;
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static struct addrinfo hints;
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struct addrinfo *res = NULL;
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int status;
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hints.ai_flags = AI_CANONNAME;
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status = getaddrinfo (host, NULL, &hints, &res);
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if (!status)
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{
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/* https://lists.gnu.org/r/bug-coreutils/2006-09/msg00300.html
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says Darwin 7.9.0 getaddrinfo returns 0 but sets
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res->ai_canonname to NULL. */
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retval = strdup (res->ai_canonname ? res->ai_canonname : host);
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if (!retval && cherror)
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*cherror = EAI_MEMORY;
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freeaddrinfo (res);
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}
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else if (cherror)
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*cherror = status;
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return retval;
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}
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/* Return a string describing the last error encountered by canon_host. */
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const char *
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ch_strerror (void)
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{
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return gai_strerror (last_cherror);
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}
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