fd-safer.c revision b7f2b4d529ee03ee0e4172cc06e7cd973bd9bef5 
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
19/* Written by Paul Eggert.  */
20
21#ifdef HAVE_CONFIG_H
22# include <config.h>
23#endif
24
25#include "unistd-safer.h"
26
27#include <errno.h>
28
29#include <unistd.h>
30#ifndef STDIN_FILENO
31# define STDIN_FILENO 0
32#endif
33#ifndef STDERR_FILENO
34# define STDERR_FILENO 2
35#endif
36
37/* Return FD, unless FD would be a copy of standard input, output, or
38   error; in that case, return a duplicate of FD, closing FD.  On
39   failure to duplicate, close FD, set errno, and return -1.  Preserve
40   errno if FD is negative, so that the caller can always inspect
41   errno when the returned value is negative.
42
43   This function is usefully wrapped around functions that return file
44   descriptors, e.g., fd_safer (open ("file", O_RDONLY)).  */
45
46int
47fd_safer (int fd)
48{
49  if (STDIN_FILENO <= fd && fd <= STDERR_FILENO)
50    {
51      int f = dup_safer (fd);
52      int e = errno;
53      close (fd);
54      errno = e;
55      fd = f;
56    }
57
58  return fd;
59}
60