1  /* Adjust a file descriptor result so that it avoids clobbering
       2     STD{IN,OUT,ERR}_FILENO, with specific flags.
       3  
       4     Copyright (C) 2005-2006, 2009-2023 Free Software 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 Paul Eggert and Eric Blake.  */
      20  
      21  #include <config.h>
      22  
      23  /* Specification.  */
      24  #include "unistd-safer.h"
      25  
      26  #include <errno.h>
      27  #include <unistd.h>
      28  
      29  /* Return FD, unless FD would be a copy of standard input, output, or
      30     error; in that case, return a duplicate of FD, closing FD.  If FLAG
      31     contains O_CLOEXEC, the returned FD will have close-on-exec
      32     semantics.  On failure to duplicate, close FD, set errno, and
      33     return -1.  Preserve errno if FD is negative, so that the caller
      34     can always inspect errno when the returned value is negative.
      35  
      36     This function is usefully wrapped around functions that return file
      37     descriptors, e.g., fd_safer_flag (open ("file", O_RDONLY | flag), flag).  */
      38  
      39  int
      40  fd_safer_flag (int fd, int flag)
      41  {
      42    if (STDIN_FILENO <= fd && fd <= STDERR_FILENO)
      43      {
      44        int f = dup_safer_flag (fd, flag);
      45        int e = errno;
      46        close (fd);
      47        errno = e;
      48        fd = f;
      49      }
      50  
      51    return fd;
      52  }