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xgethostname.c

/* xgethostname.c -- return current hostname with unlimited length

   Copyright (C) 1992, 1996, 2000, 2001, 2003, 2004, 2005, 2006, 2009
   Free Software Foundation, Inc.

   This program 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.

   This program 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 Jim Meyering */

#include <config.h>

/* Specification.  */
#include "xgethostname.h"

#include <stdlib.h>
#include <errno.h>
#include <unistd.h>

#include "xalloc.h"

#ifndef INITIAL_HOSTNAME_LENGTH
# define INITIAL_HOSTNAME_LENGTH 34
#endif

/* Return the current hostname in malloc'd storage.
   If malloc fails, exit.
   Upon any other failure, return NULL and set errno.  */
char *
xgethostname (void)
{
  char *hostname = NULL;
  size_t size = INITIAL_HOSTNAME_LENGTH;

  while (1)
    {
      /* Use SIZE_1 here rather than SIZE to work around the bug in
       SunOS 5.5's gethostname whereby it NUL-terminates HOSTNAME
       even when the name is as long as the supplied buffer.  */
      size_t size_1;

      hostname = x2realloc (hostname, &size);
      size_1 = size - 1;
      hostname[size_1 - 1] = '\0';
      errno = 0;

      if (gethostname (hostname, size_1) == 0)
      {
        if (! hostname[size_1 - 1])
          break;
      }
      else if (errno != 0 && errno != ENAMETOOLONG && errno != EINVAL
             /* OSX/Darwin does this when the buffer is not large enough */
             && errno != ENOMEM)
      {
        int saved_errno = errno;
        free (hostname);
        errno = saved_errno;
        return NULL;
      }
    }

  return hostname;
}

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