/* TCPechod.c - main, TCPechod */#define	_USE_BSD#include <sys/types.h>#include <sys/signal.h>#include <sys/socket.h>#include <sys/time.h>#include <sys/resource.h>#include <sys/wait.h>#include <sys/errno.h>#include <netinet/in.h>#include <unistd.h>#include <stdlib.h>#include <stdio.h>#include <string.h>#define	QLEN		  32	/* maximum connection queue length	*/#define	BUFSIZE		4096extern int	errno;void	reaper(int);int	TCPechod(int fd);int	errexit(const char *format, ...);int	passiveTCP(const char *service, int qlen);/*------------------------------------------------------------------------ * main - Concurrent TCP server for ECHO service *------------------------------------------------------------------------ */intmain(int argc, char *argv[]){	char	*service = "echo";	/* service name or port number	*/	struct	sockaddr_in fsin;	/* the address of a client	*/	unsigned int	alen;		/* length of client's address	*/	int	msock;			/* master server socket		*/	int	ssock;			/* slave server socket		*/	switch (argc) {	case	1:		break;	case	2:		service = argv[1];		break;	default:		errexit("usage: TCPechod [port]\n");	}	msock = passiveTCP(service, QLEN);	(void) signal(SIGCHLD, reaper);	while (1) {		alen = sizeof(fsin);		ssock = accept(msock, (struct sockaddr *)&fsin, &alen);		if (ssock < 0) {			if (errno == EINTR)				continue;			errexit("accept: %s\n", strerror(errno));		}		switch (fork()) {		case 0:		/* child */			(void) close(msock);			exit(TCPechod(ssock));		default:	/* parent */			(void) close(ssock);			break;		case -1:			errexit("fork: %s\n", strerror(errno));		}	}}/*------------------------------------------------------------------------ * TCPechod - echo data until end of file *------------------------------------------------------------------------ */intTCPechod(int fd){	char	buf[BUFSIZ];	int	cc;	while (cc = read(fd, buf, sizeof buf)) {		if (cc < 0)			errexit("echo read: %s\n", strerror(errno));		if (write(fd, buf, cc) < 0)			errexit("echo write: %s\n", strerror(errno));	}	return 0;}/*------------------------------------------------------------------------ * reaper - clean up zombie children *------------------------------------------------------------------------ */voidreaper(int sig){	int	status;	while (wait3(&status, WNOHANG, (struct rusage *)0) >= 0)		/* empty */;}