lib/xgethostname.c

   1 /* xgethostname.c -- return current hostname with unlimited length
   2
   3    Copyright (C) 1992, 1996, 2000-2001, 2003-2006, 2009-2018 Free Software
   4    Foundation, Inc.
   5
   6    This program is free software: you can redistribute it and/or modify
   7    it under the terms of the GNU General Public License as published by
   8    the Free Software Foundation; either version 3 of the License, or
   9    (at your option) any later version.
  10
  11    This program is distributed in the hope that it will be useful,
  12    but WITHOUT ANY WARRANTY; without even the implied warranty of
  13    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  14    GNU General Public License for more details.
  15
  16    You should have received a copy of the GNU General Public License
  17    along with this program.  If not, see <https://www.gnu.org/licenses/>.  */
  18
  19 /* written by Jim Meyering */
  20
  21 #include <config.h>
  22
  23 /* Specification.  */
  24 #include "xgethostname.h"
  25
  26 #include <stdlib.h>
  27 #include <errno.h>
  28 #include <unistd.h>
  29
  30 #include "xalloc.h"
  31
  32 #ifndef INITIAL_HOSTNAME_LENGTH
  33 # define INITIAL_HOSTNAME_LENGTH 34
  34 #endif
  35
  36 /* Return the current hostname in malloc'd storage.
  37    If malloc fails, exit.
  38    Upon any other failure, return NULL and set errno.  */
  39 char *
  40 xgethostname (void)
  41 {
  42   char *hostname = NULL;
  43   size_t size = INITIAL_HOSTNAME_LENGTH;
  44
  45   while (1)
  46     {
  47       /* Use SIZE_1 here rather than SIZE to work around the bug in
  48          SunOS 5.5's gethostname whereby it NUL-terminates HOSTNAME
  49          even when the name is as long as the supplied buffer.  */
  50       size_t size_1;
  51
  52       hostname = x2realloc (hostname, &size);
  53       size_1 = size - 1;
  54       hostname[size_1 - 1] = '\0';
  55       errno = 0;
  56
  57       if (gethostname (hostname, size_1) == 0)
  58         {
  59           if (! hostname[size_1 - 1])
  60             break;
  61         }
  62       else if (errno != 0 && errno != ENAMETOOLONG && errno != EINVAL
  63                /* OSX/Darwin does this when the buffer is not large enough */
  64                && errno != ENOMEM)
  65         {
  66           int saved_errno = errno;
  67           free (hostname);
  68           errno = saved_errno;
  69           return NULL;
  70         }
  71     }
  72
  73   return hostname;
  74 }