/* Test of select() substitute, reading or writing from a given file descriptor.
   Copyright (C) 2008-2026 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 Bruno Haible <bruno@clisp.org>, 2008.  */

#include <config.h>

#include <stdio.h>
#include <stdlib.h>
#include <sys/select.h>

int
main (int argc, char *argv[])
{
  if (argc == 4)
    {
      char mode = argv[1][0];

      if (mode == 'r' || mode == 'w')
        {
          int fd = atoi (argv[2]);

          if (fd >= 0)
            {
              const char *result_file_name = argv[3];
              FILE *result_file = fopen (result_file_name, "wb");

              if (result_file != NULL)
                {
                  fd_set fds;
                  struct timeval timeout;
                  int ret;

                  FD_ZERO (&fds);
                  FD_SET (fd, &fds);
                  timeout.tv_sec = 0;
                  timeout.tv_usec = 10000;
                  ret = (mode == 'r'
                         ? select (fd + 1, &fds, NULL, NULL, &timeout)
                         : select (fd + 1, NULL, &fds, NULL, &timeout));
                  if (ret < 0)
                    {
                      perror ("select failed");
                      exit (1);
                    }
                  if ((ret == 0) != ! FD_ISSET (fd, &fds))
                    {
                      fprintf (stderr, "incorrect return value\n");
                      exit (1);
                    }
                  fprintf (result_file, "%d\n", ret);
                  exit (0);
                }
            }
        }
    }
  fprintf (stderr, "Usage: test-select-fd mode fd result-file-name\n");
  exit (1);
}
