#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>


int main()
{
    struct sockaddr_in r, q;
    int listenfd, clientfd;

    if ((listenfd = socket(AF_INET, SOCK_STREAM, 0)) < 0) {
        perror("socket");
        exit(1);
    }

    memset(&r, '\0', sizeof r);
    r.sin_family = AF_INET;
    r.sin_addr.s_addr = INADDR_ANY;
    r.sin_port = htons(1234);

    if (bind(listenfd, (struct sockaddr *)&r, sizeof r)) {
        perror("bind");
        exit(1);
    }

    if (listen(listenfd, 5)) {
        perror("listen");
        exit(1);
    }

    while (1) {
	char buf[30];
	socklen_t len = sizeof q;
	if ((clientfd = accept(listenfd, (struct sockaddr *)&q, &len)) < 0) {
	    perror("accept");
	    return(1);
	}
	while (1) {
	    fd_set fdlist;
	    int from, to, n;
	    FD_ZERO(&fdlist);
	    FD_SET(clientfd, &fdlist);
	    FD_SET(0, &fdlist);
	    if (select(clientfd+1, &fdlist, NULL, NULL, NULL) < 0) {
		perror("select");
		exit(1);
	    }
	    if (FD_ISSET(0, &fdlist)) {
		from = 0;
		to = clientfd;
	    } else {
		from = clientfd;
		to = 0;
	    }
	    if ((n = read(from, buf, sizeof buf)) < 0) {
		perror("read");
		exit(1);
	    }
	    if (n == 0)
		break;
	    if (write(to, buf, n) != n) {
		perror("write");
		exit(1);
	    }
	}
	close(clientfd);
    }
}