1/* Return a safer copy of a file descriptor.
2
3   Copyright (C) 2005 Free Software Foundation, Inc.
4
5   This program is free software; you can redistribute it and/or modify
6   it under the terms of the GNU General Public License as published by
7   the Free Software Foundation; either version 2, or (at your option)
8   any later version.
9
10   This program is distributed in the hope that it will be useful,
11   but WITHOUT ANY WARRANTY; without even the implied warranty of
12   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
13   GNU General Public License for more details.
14
15   You should have received a copy of the GNU General Public License
16   along with this program; if not, write to the Free Software Foundation,
17   Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.  */
18#include <sys/cdefs.h>
19__RCSID("$NetBSD: fd-safer.c,v 1.2 2016/05/17 14:00:09 christos Exp $");
20
21
22/* Written by Paul Eggert.  */
23
24#ifdef HAVE_CONFIG_H
25# include <config.h>
26#endif
27
28#include "unistd-safer.h"
29
30#include <errno.h>
31
32#include <unistd.h>
33#ifndef STDIN_FILENO
34# define STDIN_FILENO 0
35#endif
36#ifndef STDERR_FILENO
37# define STDERR_FILENO 2
38#endif
39
40/* Return FD, unless FD would be a copy of standard input, output, or
41   error; in that case, return a duplicate of FD, closing FD.  On
42   failure to duplicate, close FD, set errno, and return -1.  Preserve
43   errno if FD is negative, so that the caller can always inspect
44   errno when the returned value is negative.
45
46   This function is usefully wrapped around functions that return file
47   descriptors, e.g., fd_safer (open ("file", O_RDONLY)).  */
48
49int
50fd_safer (int fd)
51{
52  if (STDIN_FILENO <= fd && fd <= STDERR_FILENO)
53    {
54      int f = dup_safer (fd);
55      int e = errno;
56      close (fd);
57      errno = e;
58      fd = f;
59    }
60
61  return fd;
62}
63