1 files changed, 52 insertions, 0 deletions
diff --git a/tests/fd-safer-flag.c b/tests/fd-safer-flag.c
new file mode 100644
index 00000000..4cd1b148
--- /dev/null
+++ b/tests/fd-safer-flag.c
@@ -0,0 +1,52 @@
+/* Adjust a file descriptor result so that it avoids clobbering
+   STD{IN,OUT,ERR}_FILENO, with specific flags.
+
+   Copyright (C) 2005-2006, 2009-2024 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 Eric Blake.  */
+
+#include <config.h>
+
+/* Specification.  */
+#include "unistd-safer.h"
+
+#include <errno.h>
+#include <unistd.h>
+
+/* Return FD, unless FD would be a copy of standard input, output, or
+   error; in that case, return a duplicate of FD, closing FD.  If FLAG
+   contains O_CLOEXEC, the returned FD will have close-on-exec
+   semantics.  On failure to duplicate, close FD, set errno, and
+   return -1.  Preserve errno if FD is negative, so that the caller
+   can always inspect errno when the returned value is negative.
+
+   This function is usefully wrapped around functions that return file
+   descriptors, e.g., fd_safer_flag (open ("file", O_RDONLY | flag), flag).  */
+
+int
+fd_safer_flag (int fd, int flag)
+{
+  if (STDIN_FILENO <= fd && fd <= STDERR_FILENO)
+    {
+      int f = dup_safer_flag (fd, flag);
+      int e = errno;
+      close (fd);
+      errno = e;
+      fd = f;
+    }
+
+  return fd;
+}