1 files changed, 123 insertions, 0 deletions
diff --git a/lib/isapipe.c b/lib/isapipe.c
new file mode 100644
index 0000000..467ed00
--- /dev/null
+++ b/lib/isapipe.c
@@ -0,0 +1,123 @@
+/* Test whether a file descriptor is a pipe.
+
+   Copyright (C) 2006, 2008-2022 Free Software Foundation, Inc.
+
+   This file is free software: you can redistribute it and/or modify
+   it under the terms of the GNU Lesser General Public License as
+   published by the Free Software Foundation, either version 3 of the
+   License, or (at your option) any later version.
+
+   This file 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 Lesser General Public License for more details.
+
+   You should have received a copy of the GNU Lesser General Public License
+   along with this program.  If not, see <https://www.gnu.org/licenses/>.  */
+
+/* Written by Paul Eggert.  */
+
+#include <config.h>
+
+#include "isapipe.h"
+
+#include <errno.h>
+
+#if defined _WIN32 && ! defined __CYGWIN__
+/* Windows platforms.  */
+
+/* Get GetFileType.  */
+# include <windows.h>
+
+/* Get _get_osfhandle.  */
+# if GNULIB_MSVC_NOTHROW
+#  include "msvc-nothrow.h"
+# else
+#  include <io.h>
+# endif
+
+int
+isapipe (int fd)
+{
+  HANDLE h = (HANDLE) _get_osfhandle (fd);
+
+  if (h == INVALID_HANDLE_VALUE)
+    {
+      errno = EBADF;
+      return -1;
+    }
+
+  return (GetFileType (h) == FILE_TYPE_PIPE);
+}
+
+#else
+/* Unix platforms.  */
+
+# include <stdbool.h>
+# include <sys/types.h>
+# include <sys/stat.h>
+# include <unistd.h>
+
+/* The maximum link count for pipes; (nlink_t) -1 if not known.  */
+# ifndef PIPE_LINK_COUNT_MAX
+#  define PIPE_LINK_COUNT_MAX ((nlink_t) (-1))
+# endif
+
+/* Return 1 if FD is a pipe, 0 if not, -1 (setting errno) on error.
+
+   Test fairly strictly whether FD is a pipe.  lseek and checking for
+   ESPIPE does not suffice, since many non-pipe files cause lseek to
+   fail with errno == ESPIPE.  */
+
+int
+isapipe (int fd)
+{
+  nlink_t pipe_link_count_max = PIPE_LINK_COUNT_MAX;
+  bool check_for_fifo = (HAVE_FIFO_PIPES == 1);
+  struct stat st;
+  int fstat_result = fstat (fd, &st);
+
+  if (fstat_result != 0)
+    return fstat_result;
+
+  /* We want something that succeeds only for pipes, but on
+     POSIX-conforming hosts S_ISFIFO succeeds for both FIFOs and pipes
+     and we know of no portable, reliable way to distinguish them in
+     general.  However, in practice pipes always have a link count <=
+     PIPE_LINK_COUNT_MAX (unless someone attaches them to the file
+     system name space using fattach, in which case they're not really
+     pipes any more), so test for that as well.
+
+     On Darwin 7.7, pipes are sockets, so check for those instead.  */
+
+  if (! ((HAVE_FIFO_PIPES == 0 || HAVE_FIFO_PIPES == 1)
+         && PIPE_LINK_COUNT_MAX != (nlink_t) -1)
+      && (S_ISFIFO (st.st_mode) | S_ISSOCK (st.st_mode)))
+    {
+      int fd_pair[2];
+      int pipe_result = pipe (fd_pair);
+      if (pipe_result != 0)
+        return pipe_result;
+      else
+        {
+          struct stat pipe_st;
+          int fstat_pipe_result = fstat (fd_pair[0], &pipe_st);
+          int fstat_pipe_errno = errno;
+          close (fd_pair[0]);
+          close (fd_pair[1]);
+          if (fstat_pipe_result != 0)
+            {
+              errno = fstat_pipe_errno;
+              return fstat_pipe_result;
+            }
+          check_for_fifo = (S_ISFIFO (pipe_st.st_mode) != 0);
+          pipe_link_count_max = pipe_st.st_nlink;
+        }
+    }
+
+  return
+    (st.st_nlink <= pipe_link_count_max
+     && (check_for_fifo ? S_ISFIFO (st.st_mode) : S_ISSOCK (st.st_mode)));
+}
+
+#endif