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diff --git a/tests/test-dup2.c b/tests/test-dup2.c
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+/* Test duplicating file descriptors.
+ Copyright (C) 2009-2022 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 Eric Blake <ebb9@byu.net>, 2009. */
+
+#include <config.h>
+
+#include <unistd.h>
+
+#include "signature.h"
+SIGNATURE_CHECK (dup2, int, (int, int));
+
+#include <errno.h>
+#include <fcntl.h>
+
+#if HAVE_SYS_RESOURCE_H
+# include <sys/resource.h>
+#endif
+
+#include "binary-io.h"
+
+#if GNULIB_TEST_CLOEXEC
+# include "cloexec.h"
+#endif
+
+#if defined _WIN32 && ! defined __CYGWIN__
+/* Get declarations of the native Windows API functions. */
+# define WIN32_LEAN_AND_MEAN
+# include <windows.h>
+/* Get _get_osfhandle. */
+# if GNULIB_MSVC_NOTHROW
+# include "msvc-nothrow.h"
+# else
+# include <io.h>
+# endif
+#endif
+
+#include "macros.h"
+
+/* Return non-zero if FD is open. */
+static int
+is_open (int fd)
+{
+#if defined _WIN32 && ! defined __CYGWIN__
+ /* On native Windows, the initial state of unassigned standard file
+ descriptors is that they are open but point to an
+ INVALID_HANDLE_VALUE, and there is no fcntl. */
+ return (HANDLE) _get_osfhandle (fd) != INVALID_HANDLE_VALUE;
+#else
+# ifndef F_GETFL
+# error Please port fcntl to your platform
+# endif
+ return 0 <= fcntl (fd, F_GETFL);
+#endif
+}
+
+#if GNULIB_TEST_CLOEXEC
+/* Return non-zero if FD is open and inheritable across exec/spawn. */
+static int
+is_inheritable (int fd)
+{
+# if defined _WIN32 && ! defined __CYGWIN__
+ /* On native Windows, the initial state of unassigned standard file
+ descriptors is that they are open but point to an
+ INVALID_HANDLE_VALUE, and there is no fcntl. */
+ HANDLE h = (HANDLE) _get_osfhandle (fd);
+ DWORD flags;
+ if (h == INVALID_HANDLE_VALUE || GetHandleInformation (h, &flags) == 0)
+ return 0;
+ return (flags & HANDLE_FLAG_INHERIT) != 0;
+# else
+# ifndef F_GETFD
+# error Please port fcntl to your platform
+# endif
+ int i = fcntl (fd, F_GETFD);
+ return 0 <= i && (i & FD_CLOEXEC) == 0;
+# endif
+}
+#endif /* GNULIB_TEST_CLOEXEC */
+
+#if !O_BINARY
+# define set_binary_mode(f,m) zero ()
+static int zero (void) { return 0; }
+#endif
+
+/* Return non-zero if FD is open in the given MODE, which is either
+ O_TEXT or O_BINARY. */
+static int
+is_mode (int fd, int mode)
+{
+ int value = set_binary_mode (fd, O_BINARY);
+ set_binary_mode (fd, value);
+ return mode == value;
+}
+
+int
+main (void)
+{
+ const char *file = "test-dup2.tmp";
+ char buffer[1];
+ int bad_fd = getdtablesize ();
+ int fd = open (file, O_CREAT | O_TRUNC | O_RDWR, 0600);
+
+ /* Assume std descriptors were provided by invoker. */
+ ASSERT (STDERR_FILENO < fd);
+ ASSERT (is_open (fd));
+ /* Ignore any other fd's leaked into this process. */
+ close (fd + 1);
+ close (fd + 2);
+ ASSERT (!is_open (fd + 1));
+ ASSERT (!is_open (fd + 2));
+
+ /* Assigning to self must be a no-op. */
+ ASSERT (dup2 (fd, fd) == fd);
+ ASSERT (is_open (fd));
+
+ /* The source must be valid. */
+ errno = 0;
+ ASSERT (dup2 (-1, fd) == -1);
+ ASSERT (errno == EBADF);
+ close (99);
+ errno = 0;
+ ASSERT (dup2 (99, fd) == -1);
+ ASSERT (errno == EBADF);
+ errno = 0;
+ ASSERT (dup2 (AT_FDCWD, fd) == -1);
+ ASSERT (errno == EBADF);
+ ASSERT (is_open (fd));
+
+ /* If the source is not open, then the destination is unaffected. */
+ errno = 0;
+ ASSERT (dup2 (fd + 1, fd + 1) == -1);
+ ASSERT (errno == EBADF);
+ ASSERT (!is_open (fd + 1));
+ errno = 0;
+ ASSERT (dup2 (fd + 1, fd) == -1);
+ ASSERT (errno == EBADF);
+ ASSERT (is_open (fd));
+
+ /* The destination must be valid. */
+ errno = 0;
+ ASSERT (dup2 (fd, -2) == -1);
+ ASSERT (errno == EBADF);
+ if (bad_fd > 256)
+ {
+ ASSERT (dup2 (fd, 255) == 255);
+ ASSERT (dup2 (fd, 256) == 256);
+ ASSERT (close (255) == 0);
+ ASSERT (close (256) == 0);
+ }
+ ASSERT (dup2 (fd, bad_fd - 1) == bad_fd - 1);
+ ASSERT (close (bad_fd - 1) == 0);
+ errno = 0;
+ ASSERT (dup2 (fd, bad_fd) == -1);
+ ASSERT (errno == EBADF);
+
+ /* Using dup2 can skip fds. */
+ ASSERT (dup2 (fd, fd + 2) == fd + 2);
+ ASSERT (is_open (fd));
+ ASSERT (!is_open (fd + 1));
+ ASSERT (is_open (fd + 2));
+
+ /* Verify that dup2 closes the previous occupant of a fd. */
+ ASSERT (open ("/dev/null", O_WRONLY, 0600) == fd + 1);
+ ASSERT (dup2 (fd + 1, fd) == fd);
+ ASSERT (close (fd + 1) == 0);
+ ASSERT (write (fd, "1", 1) == 1);
+ ASSERT (dup2 (fd + 2, fd) == fd);
+ ASSERT (lseek (fd, 0, SEEK_END) == 0);
+ ASSERT (write (fd + 2, "2", 1) == 1);
+ ASSERT (lseek (fd, 0, SEEK_SET) == 0);
+ ASSERT (read (fd, buffer, 1) == 1);
+ ASSERT (*buffer == '2');
+
+#if GNULIB_TEST_CLOEXEC
+ /* Any new fd created by dup2 must not be cloexec. */
+ ASSERT (close (fd + 2) == 0);
+ ASSERT (dup_cloexec (fd) == fd + 1);
+ ASSERT (!is_inheritable (fd + 1));
+ ASSERT (dup2 (fd + 1, fd + 1) == fd + 1);
+ ASSERT (!is_inheritable (fd + 1));
+ ASSERT (dup2 (fd + 1, fd + 2) == fd + 2);
+ ASSERT (!is_inheritable (fd + 1));
+ ASSERT (is_inheritable (fd + 2));
+ errno = 0;
+ ASSERT (dup2 (fd + 1, -1) == -1);
+ ASSERT (errno == EBADF);
+ ASSERT (!is_inheritable (fd + 1));
+#endif
+
+ /* On systems that distinguish between text and binary mode, dup2
+ reuses the mode of the source. */
+ set_binary_mode (fd, O_BINARY);
+ ASSERT (is_mode (fd, O_BINARY));
+ ASSERT (dup2 (fd, fd + 1) == fd + 1);
+ ASSERT (is_mode (fd + 1, O_BINARY));
+ set_binary_mode (fd, O_TEXT);
+ ASSERT (is_mode (fd, O_TEXT));
+ ASSERT (dup2 (fd, fd + 1) == fd + 1);
+ ASSERT (is_mode (fd + 1, O_TEXT));
+
+ /* Clean up. */
+ ASSERT (close (fd + 2) == 0);
+ ASSERT (close (fd + 1) == 0);
+ ASSERT (close (fd) == 0);
+ ASSERT (unlink (file) == 0);
+
+ return 0;
+}