/* UDPtimed.c - main */#include <sys/types.h>#include <sys/socket.h>#include <netinet/in.h>#include <stdio.h>#include <time.h>#include <string.h>extern int	errno;int	passiveUDP(const char *service);int	errexit(const char *format, ...);#define	UNIXEPOCH	2208988800UL	/* UNIX epoch, in UCT secs	*//*------------------------------------------------------------------------ * main - Iterative UDP server for TIME service *------------------------------------------------------------------------ */intmain(int argc, char *argv[]){	struct sockaddr_in fsin;	/* the from address of a client	*/	char	*service = "time";	/* service name or port number	*/	char	buf[1];			/* "input" buffer; any size > 0	*/	int	sock;			/* server socket		*/	time_t	now;			/* current time			*/	unsigned int	alen;		/* from-address length		*/	switch (argc) {	case	1:		break;	case	2:		service = argv[1];		break;	default:		errexit("usage: UDPtimed [port]\n");	}	sock = passiveUDP(service);	while (1) {		alen = sizeof(fsin);		if (recvfrom(sock, buf, sizeof(buf), 0,				(struct sockaddr *)&fsin, &alen) < 0)			errexit("recvfrom: %s\n", strerror(errno));		(void) time(&now);		now = htonl((unsigned long)(now + UNIXEPOCH));		(void) sendto(sock, (char *)&now, sizeof(now), 0,			(struct sockaddr *)&fsin, sizeof(fsin));	}}