vn.c

/* vn.c generic virtual network client/server
 * via UDP
 * Author: Daniele Lacamera
 * License MIT
 */
#include <sys/socket.h>
#include <sys/types.h>
#include <linux/if_tun.h>
#include <stdio.h>
#include <stdint.h>
#include <unistd.h>
#include <stdlib.h>
#include <netinet/ip.h>
#include <fcntl.h>
#include <poll.h>
#include <net/if.h>
#include <sys/ioctl.h>
#include <string.h>
#include <sys/poll.h>
#include <arpa/inet.h>


#define MTU 1500


uint8_t buf[MTU];

int main(int argc, char *argv[])
{
    int sd = socket(AF_INET, SOCK_DGRAM, 0);
    int td = open("/dev/net/tun", O_RDWR);
    struct sockaddr_in saddr = { }, daddr = { };
    struct ifreq ifr;
    socklen_t sl = sizeof(struct sockaddr_in);
    int r;
    struct pollfd pfd[2];

    memset(&ifr, 0, sizeof(ifr));
    ifr.ifr_flags = IFF_TAP | IFF_NO_PI;
    strncpy(ifr.ifr_name, "vn0", IFNAMSIZ);
    if(ioctl(td, TUNSETIFF, &ifr) < 0) {
        perror("ioctl");
        exit(3);
    }


    if (argc == 1) {
        printf("Running as server\n");
    } else if (argc == 2) {
        printf("Running as client\n");
        daddr.sin_family = AF_INET;
        daddr.sin_port = ntohs(12122);
        daddr.sin_addr.s_addr = inet_addr(argv[1]);
    } else {
        printf("Too many arguments.\n");
        exit(1);
    }



    saddr.sin_port = ntohs(12122);
    if (sd < 0) {
        perror("socket");
        exit(1);
    }

    if (bind(sd, (struct sockaddr *)&saddr, sizeof(struct sockaddr_in)) < 0) {
        perror("bind");
        exit(2);
    }

    while (1) {
        pfd[0].fd = sd;
        pfd[1].fd = td;
        pfd[0].events = POLLIN;
        pfd[1].events = POLLIN;

        r = poll(pfd, 2, -1);
        if (r > 0) {
            if ((pfd[0].revents & POLLIN) == POLLIN) {
                r = recvfrom(sd, buf, MTU, 0, (struct sockaddr *)&daddr, &sl);
                if (r > 0) {
                    printf("> %d\n", r);
                    write(td, buf, r);
                }
            }
            if ((pfd[1].revents & POLLIN) == POLLIN) {
                r = read(td, buf, MTU);
                if ((r > 0) && (daddr.sin_addr.s_addr != 0)) {
                    printf("< %d\n", r);
                    sendto(sd, buf, r, 0, (struct sockaddr *)&daddr, sizeof(struct sockaddr_in));
                }
            }
        }
    }
}