/* TCPmechod.c - main, echo */

#include <sys/types.h>
#include <sys/socket.h>
#include <sys/time.h>
#include <netinet/in.h>

#include <unistd.h>
#include <string.h>
#include <stdio.h>

#define	QLEN		   5	/* maximum connection queue length	*/
#define	BUFSIZE		4096

extern int	errno;
int		errexit(const char *format, ...);
int		passiveTCP(const char *service, int qlen);
int		echo(int fd);

/*------------------------------------------------------------------------
 * main - Concurrent TCP server for ECHO service
 *------------------------------------------------------------------------
 */
int
main(int argc, char *argv[])
{
	char	*service = "echo";	/* service name or port number	*/
	struct sockaddr_in fsin;	/* the from address of a client	*/
	int	msock;			/* master server socket		*/
	fd_set	rfds;			/* read file descriptor set	*/
	fd_set	afds;			/* active file descriptor set	*/
	int	alen;			/* from-address length		*/
	int	fd, nfds;
	
	switch (argc) {
	case	1:
		break;
	case	2:
		service = argv[1];
		break;
	default:
		errexit("usage: TCPmechod [port]\n");
	}

	msock = passiveTCP(service, QLEN);

	nfds = getdtablesize();
	FD_ZERO(&afds);
	FD_SET(msock, &afds);

	while (1) {
		memcpy(&rfds, &afds, sizeof(rfds));

		if (select(nfds, &rfds, (fd_set *)0, (fd_set *)0,
				(struct timeval *)0) < 0)
			errexit("select: %s\n", strerror(errno));
		if (FD_ISSET(msock, &rfds)) {
			int	ssock;

			alen = sizeof(fsin);
			ssock = accept(msock, (struct sockaddr *)&fsin,
				&alen);
			if (ssock < 0)
				errexit("accept: %s\n",
					strerror(errno));
			FD_SET(ssock, &afds);
		}
		for (fd=0; fd<nfds; ++fd)
			if (fd != msock && FD_ISSET(fd, &rfds))
				if (echo(fd) == 0) {
					(void) close(fd);
					FD_CLR(fd, &afds);
				}
	}
}

/*------------------------------------------------------------------------
 * echo - echo one buffer of data, returning byte count
 *------------------------------------------------------------------------
 */
int
echo(int fd)
{
	char	buf[BUFSIZ];
	int	cc;

	cc = read(fd, buf, sizeof buf);
	if (cc < 0)
		errexit("echo read: %s\n", strerror(errno));
	if (cc && write(fd, buf, cc) < 0)
		errexit("echo write: %s\n", strerror(errno));
	return cc;
}