#include <sys/types.h>
#include <sys/stat.h>
#include <sys/socket.h>
#include <unistd.h>
#include <errno.h>
#include <string.h>
#include <stdio.h>

void
is_socket(int fd)
{
	struct stat buf;
	memset(&buf, 0, sizeof(buf));
	int status = fstat(fd, &buf);
	if (status < 0)
	{
		printf("fstat() failed with %d\n", errno);
		return;
	}

	if (S_ISSOCK(buf.st_mode))
		printf("fd %d is a socket\n", fd);
	else
		printf("fd %d is not a socket\n", fd);
}

int
main()
{
	int status = 0;

	int fd = socket(AF_INET, SOCK_STREAM, 0);
	if (fd < 0)
	{
		printf("socket() failed with %d\n", errno);
		return 1;
	}

	is_socket(fd);

	int fd2 = 13;
	status = dup2(fd, fd2);
	if (status < 0)
	{
		printf("dup2() failed with %d\n", errno);
		return 1;
	}

	is_socket(fd2);

	return 0;
}