gnulib/lib/xgethostname.c

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

   Copyright (C) 1992, 1996, 2000-2001, 2003-2006, 2009-2020 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 <https://www.gnu.org/licenses/>.  */

/* written by Jim Meyering */

#include <config.h>

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

#include <stdlib.h>
#include <errno.h>
#include <string.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;
        }
    }

  /* Shrink HOSTNAME before returning it.  */
  {
    size_t actual_size = strlen (hostname) + 1;
    if (actual_size < size)
      {
        char *shrinked_hostname = realloc (hostname, actual_size);
        if (shrinked_hostname != NULL)
          hostname = shrinked_hostname;
      }
  }

  return hostname;
}