#include <stdio.h>#include <sys/types.h>#include <sys/fcntl.h>#include <sys/socket.h>#include <netinet/in.h>extern int errno;#define SERV_HOST_ADDR  "128.220.101.4"#define SERV_TCP_PORT   6000main(){	int fd;	struct sockaddr_in	my_addr;	struct sockaddr_in	serv_addr;	char buf[128];	void echo_driver(int, struct sockaddr_in *);	if ((fd = net_open ("/dev/udp", O_RDWR)) < 0)	{		fprintf (stderr, "open failed.\n");		exit (-1);	}	/*	 * bind any address to us.	 */	bzero((char *) &my_addr, sizeof(my_addr));	my_addr.sin_family      = AF_INET;	my_addr.sin_addr.s_addr = htonl (INADDR_ANY);	my_addr.sin_port        = htons(0);	fd = net_bind (fd, &my_addr, sizeof (struct sockaddr_in));	/*	 * set up server's address	 */	bzero((char *) &serv_addr, sizeof(serv_addr));	serv_addr.sin_family      = AF_INET;	serv_addr.sin_addr.s_addr = inet_addr (SERV_HOST_ADDR);	serv_addr.sin_port        = htons(SERV_TCP_PORT);	echo_driver (fd, &serv_addr);	close (fd);	exit (0);}voidecho_driver(int fd, struct sockaddr_in *serv_addr){	char buf[512];	int n;	struct sockaddr_in	fm_addr;	while ((n = read (0, buf, sizeof (buf))) != 0)	{		net_send (fd, buf, n, serv_addr, sizeof (struct sockaddr_in));		n = net_recv (fd, buf, sizeof (buf), &fm_addr, sizeof (struct sockaddr_in));		write (1, buf, n);	}	return;}