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/* localhost.c - A slightly more convenient wrapper for gethostname
Copyright (C) 1996-2025 Free Software Foundation, Inc.
This file is part of GNU Inetutils.
GNU Inetutils is free software: you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation, either version 3 of the License, or (at
your option) any later version.
GNU Inetutils is distributed in the hope that it will be useful, but
WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
General Public License for more details.
You should have received a copy of the GNU General Public License
along with this program. If not, see `http://www.gnu.org/licenses/'. */
/* Written by Miles Bader. */
#include <config.h>
#include <unistd.h>
#include <stdlib.h>
#include <stdint.h>
#include <string.h>
#include <errno.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <netdb.h>
/* Return the name of the localhost. This is just a wrapper for gethostname,
taking care of allocating a big enough buffer, and caching the result
after the first call (so the result should be copied before modification).
If something goes wrong, 0 is returned, and errno is set.
*/
/* We no longer use static buffers, as it is too dangerous and
it causes subtile bugs. */
char *
localhost (void)
{
char *buf = NULL;
size_t buf_len = 0;
int status = 0;
do
{
char *tmp;
errno = 0;
buf_len += 256; /* Initial guess */
tmp = realloc (buf, buf_len);
if (tmp == NULL)
{
errno = ENOMEM;
free (buf);
return 0;
}
else
buf = tmp;
}
while (((status = gethostname (buf, buf_len)) == 0
&& !memchr (buf, '\0', buf_len))
#ifdef ENAMETOOLONG
|| errno == ENAMETOOLONG
#endif
);
if (status != 0 && errno != 0)
/* gethostname failed, abort. */
{
free (buf);
buf = 0;
}
else
/* Determine FQDN. */
{
#if HAVE_DECL_GETADDRINFO
int rc;
struct addrinfo hints, *res;
char fqdn[NI_MAXHOST];
memset (&hints, 0, sizeof (hints));
hints.ai_family = AF_INET;
rc = getaddrinfo (buf, NULL, &hints, &res);
if (!rc)
{
/* Back resolving as official host name. */
rc = getnameinfo (res->ai_addr, res->ai_addrlen,
fqdn, sizeof (fqdn), NULL, 0, NI_NAMEREQD);
if (!rc)
{
free (buf);
buf = strdup (fqdn);
}
freeaddrinfo (res);
}
#else /* !HAVE_DECL_GETADDRINFO */
struct hostent *hp = gethostbyname (buf);
if (hp)
{
struct in_addr addr;
addr.s_addr = *(unsigned int *) hp->h_addr;
hp = gethostbyaddr ((char *) &addr, sizeof (addr), AF_INET);
if (hp)
{
free (buf);
buf = strdup (hp->h_name);
}
}
#endif /* !HAVE_DECL_GETADDRINFO */
}
return buf;
}
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