#include <stdio.h>  /* printf */
#include <sys/socket.h>  /* socket, bind, listen */
#include <arpa/inet.h>  /* htonl */
#include <string.h>  /* memcpy */
#include <sys/select.h>  /* select */
#include <unistd.h>  /* write */
#include <netdb.h>  /* gethostbyname */
#include <stdlib.h>  /* free */

int createTCPserverSocket(int port) {
    int s, len;
    struct sockaddr_in name;

    /* Create the socket. */
    s = socket(AF_INET, SOCK_STREAM, 0);

    /* Create the address of the server. */
    name.sin_family = AF_INET;
    name.sin_port = htons(port);
    name.sin_addr.s_addr = htonl(INADDR_ANY); /* Use the wildcard address.*/
    len = sizeof(struct sockaddr_in);

    /* Bind the socket to the address. */
   if( bind(s, (struct sockaddr *) &name, len))
		printf("bind error");

    /* Listen for connections.  */
    listen(s, 5);
    return(s);
}

int createTCPclientSocket(char *hostname, int port) {
    int s, len;
    struct hostent *hp;
    struct sockaddr_in name;

    /* Look up our host's network address.*/
    hp = gethostbyname(hostname);

    /* Create a socket in the INET domain.*/
    s = socket(AF_INET, SOCK_STREAM, 0);

    /* Create the address of the server. */
    name.sin_family = AF_INET;
    name.sin_port = htons(port);
    memcpy(&name.sin_addr, hp->h_addr_list[0], hp->h_length);
    len = sizeof(struct sockaddr_in);

    /* Connect to the server. */
    connect(s, (struct sockaddr *) &name, len);
    return s;
}

#define BUFF_SIZE  10

void * TCPRelay(void * arg){  /* int arg[]  */
    fd_set readfds, readfdsCopy;
    int maxfd, n;
    int * sockets = (int*) arg;
    char buff[BUFF_SIZE];

    FD_ZERO(&readfdsCopy);
    FD_SET(sockets[0],&readfdsCopy);
    FD_SET(sockets[1],&readfdsCopy);
    maxfd = sockets[0] > sockets[1]?sockets[0]:sockets[1];
    maxfd++;
    for(;;){
        memcpy(&readfds, &readfdsCopy, sizeof(fd_set));
        n = select(maxfd, &readfds, (fd_set *) 0, (fd_set *) 0, NULL);
        if (n > 0) {
            if (FD_ISSET(sockets[0], &readfds)) {
                if ((n=read(sockets[0], buff,  BUFF_SIZE)) <= 0) break;
                else if (write(sockets[1], buff, n) <= 0)  break;
            }
            if (FD_ISSET(sockets[1], &readfds)) {
                if ((n=read(sockets[1], buff,  BUFF_SIZE)) <= 0) break;
                else if (write(sockets[0], buff, n) <= 0) break;
            }
        }
    }
    close(sockets[0]);
    close(sockets[1]);
    free (sockets);
}