/* TCPecho.c - main, TCPecho */#include <unistd.h>#include <stdlib.h>#include <string.h>#include <stdio.h>extern int	errno;int	TCPecho(const char *host, const char *service);int	errexit(const char *format, ...);int	connectTCP(const char *host, const char *service);#define	LINELEN		128/*------------------------------------------------------------------------ * main - TCP client for ECHO service *------------------------------------------------------------------------ */intmain(int argc, char *argv[]){	char	*host = "localhost";	/* host to use if none supplied	*/	char	*service = "echo";	/* default service name		*/	switch (argc) {	case 1:		host = "localhost";		break;	case 3:		service = argv[2];		/* FALL THROUGH */	case 2:		host = argv[1];		break;	default:		fprintf(stderr, "usage: TCPecho [host [port]]\n");		exit(1);	}	TCPecho(host, service);	exit(0);}/*------------------------------------------------------------------------ * TCPecho - send input to ECHO service on specified host and print reply *------------------------------------------------------------------------ */intTCPecho(const char *host, const char *service){	char	buf[LINELEN+1];		/* buffer for one line of text	*/	int	s, n;			/* socket descriptor, read count*/	int	outchars, inchars;	/* characters sent and received	*/	s = connectTCP(host, service);	while (fgets(buf, sizeof(buf), stdin)) {		buf[LINELEN] = '\0';	/* insure line null-terminated	*/		outchars = strlen(buf);		(void) write(s, buf, outchars);		/* read it back */		for (inchars = 0; inchars < outchars; inchars+=n ) {			n = read(s, &buf[inchars], outchars - inchars);			if (n < 0)				errexit("socket read failed: %s\n",					strerror(errno));		}		fputs(buf, stdout);	}}