1 files changed, 66 insertions, 0 deletions
diff --git a/gl/lib/stdopen.c b/gl/lib/stdopen.c
new file mode 100644
index 0000000..e9a8e49
--- /dev/null
+++ b/gl/lib/stdopen.c
@@ -0,0 +1,66 @@
+/* stdopen.c - ensure that the three standard file descriptors are in use
+
+   Copyright (C) 2005-2006, 2019-2023 Free Software Foundation, Inc.
+
+   This program is free software: you can redistribute it and/or modify
+   it under the terms of the GNU General Public License as published by
+   the Free Software Foundation, either version 3 of the License, or
+   (at your option) any later version.
+
+   This program is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+   GNU General Public License for more details.
+
+   You should have received a copy of the GNU General Public License
+   along with this program.  If not, see <https://www.gnu.org/licenses/>.  */
+
+/* Written by Paul Eggert and Jim Meyering.  */
+
+#include <config.h>
+
+#include "stdopen.h"
+
+#include <sys/stat.h>
+#include <fcntl.h>
+#include <unistd.h>
+#include <errno.h>
+
+/* Try to ensure that all of the standard file numbers (0, 1, 2)
+   are in use.  Without this, each application would have to guard
+   every call to open, dup, fopen, etc. with tests to ensure they
+   don't use one of the special file numbers when opening a file.
+   Return zero if successful, an errno value if at least one of
+   the file descriptors is initially closed and could not be opened.  */
+
+int
+stdopen (void)
+{
+  int fd;
+  for (fd = STDIN_FILENO; fd <= STDERR_FILENO; fd++)
+    {
+      if (fcntl (fd, F_GETFD) < 0)
+        {
+          /* Open /dev/null with the contrary mode so that the typical
+             read (stdin) or write (stdout, stderr) operation will fail.
+             With descriptor 0, we can do even better on systems that
+             have /dev/full, by opening that write-only instead of
+             /dev/null.  The only drawback is that a write-provoked
+             failure comes with a misleading errno value, ENOSPC.  */
+          int mode = fd == STDIN_FILENO ? O_WRONLY : O_RDONLY;
+          int full_fd = fd == STDIN_FILENO ? open ("/dev/full", mode) : -1;
+          int new_fd = full_fd < 0 ? open ("/dev/null", mode) : full_fd;
+          if (new_fd < 0)
+            return errno;
+          if (STDERR_FILENO < new_fd)
+            {
+              /* 0, 1, and 2 are already open somehow.
+                 Our is not to reason why.  */
+              close (new_fd);
+              return 0;
+            }
+        }
+    }
+
+  return 0;
+}