lib/xgethostname.c

   1 /* xgethostname.c -- return current hostname with unlimited length
   2
   3    Copyright (C) 1992, 1996, 2000-2001, 2003-2006, 2009-2020 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 <string.h>
  29 #include <unistd.h>
  30
  31 #include "xalloc.h"
  32
  33 #ifndef INITIAL_HOSTNAME_LENGTH
  34 # define INITIAL_HOSTNAME_LENGTH 34
  35 #endif
  36
  37 /* Return the current hostname in malloc'd storage.
  38    If malloc fails, exit.
  39    Upon any other failure, return NULL and set errno.  */
  40 char *
  41 xgethostname (void)
  42 {
  43   char *hostname = NULL;
  44   size_t size = INITIAL_HOSTNAME_LENGTH;
  45
  46   while (1)
  47     {
  48       /* Use SIZE_1 here rather than SIZE to work around the bug in
  49          SunOS 5.5's gethostname whereby it NUL-terminates HOSTNAME
  50          even when the name is as long as the supplied buffer.  */
  51       size_t size_1;
  52
  53       hostname = x2realloc (hostname, &size);
  54       size_1 = size - 1;
  55       hostname[size_1 - 1] = '\0';
  56       errno = 0;
  57
  58       if (gethostname (hostname, size_1) == 0)
  59         {
  60           if (! hostname[size_1 - 1])
  61             break;
  62         }
  63       else if (errno != 0 && errno != ENAMETOOLONG && errno != EINVAL
  64                /* OSX/Darwin does this when the buffer is not large enough */
  65                && errno != ENOMEM)
  66         {
  67           int saved_errno = errno;
  68           free (hostname);
  69           errno = saved_errno;
  70           return NULL;
  71         }
  72     }
  73
  74   /* Shrink HOSTNAME before returning it.  */
  75   {
  76     size_t actual_size = strlen (hostname) + 1;
  77     if (actual_size < size)
  78       {
  79         char *shrinked_hostname = realloc (hostname, actual_size);
  80         if (shrinked_hostname != NULL)
  81           hostname = shrinked_hostname;
  82       }
  83   }
  84
  85   return hostname;
  86 }