/*
   cattap.c
   2004 David Baird
   This program demonstrates how to cat data from a tun interface.
   tun gives user space programs the ability to tunnel network traffic
   through custom protocols and hardware.

   Resources:
   http://vtun.sourceforge.net/tun/
   http://www.sics.se/~adam/uip/download.html (uip)
   /usr/src/linux/Documentation/networking/tuntap.txt
   rainbow.nmt.edu: /usr/src/linux-2.4/Documentation/networking/tuntap.txt
   qemu-0.6.0/vl.c tun_open
*/

#include <fcntl.h> // open
#include <stdio.h>
#include <stdlib.h> // system
#include <sys/time.h> // struct timeval
#include <sys/ioctl.h>
#include <sys/select.h>
#include <sys/socket.h> // ifru_* type completion
#include <linux/if.h> // struct ifreq
#include <linux/if_tun.h> // constants: IFF_TUN, etc.

#define TUNDEV "/dev/net/tun"

int tun_init(char *ipaddr) {
    int fd;
    struct ifreq ifr;
    char buf[512];
    fd = open(TUNDEV, O_RDWR);
    if(fd == -1) {
        perror(TUNDEV);
        exit(1);
    }
    bzero(&ifr, sizeof(ifr));
    ifr.ifr_flags = IFF_TAP | IFF_NO_PI;
    strcpy();
    if(ioctl(fd, TUNSETIFF, (void *) &ifr) < 0) {
        close(fd);
        perror("ioctl TUNSETIFF");
        exit(1);
    }
    //sprintf(buf, "/sbin/ifconfig tun0 inet %s", ipaddr);
    sprintf(buf, "/sbin/ifconfig tun0 %s netmask 255.255.255.0", ipaddr);
    system(buf);
    return fd;
}

int my_select(int fd, int msec_timeout) {
    fd_set fdset;
    struct timeval tv;
    int ret;
    tv.tv_sec = msec_timeout / 1000;
    tv.tv_usec = (msec_timeout - tv.tv_sec * 1000) * 1000;
    FD_ZERO(&fdset);
    FD_SET(fd, &fdset);
    ret = select(fd + 1, &fdset, NULL, NULL, &tv);
    return ret;
}

int main() {
    int tunfd;
    const int BUF_SIZE = 2048;
    char buf[BUF_SIZE];
    int ret;
    tunfd = tun_init("192.168.3.33");
    while(1) {
        if(my_select(tunfd, 100)) {
            //printf("selected\n");
            ret = read(tunfd, buf, BUF_SIZE);
            fwrite(buf, ret, 1, stdout);
            fwrite("*--*", 4, 1, stdout);
            fflush(stdout);
        }
    }
    return 0;
}