igmp-querier.c

/**
 * igmp-querier.c - IGMP Querier for Multicast DNS
 *
 * Copyright (c) 2014, Anthony Dong <aanthony.dong@gmail.com>
 * All rights reserved.
 *
 * This software may be modified and distributed under the terms
 * of the BSD license.  See the LICENSE file for details.
 *
 * Original work by Daniel Lorch <dlorch@gmail.com>
 * Rewritten to use libnet 1.1
 * Many thanks go to Marc Cullen <mcbugs000@gmail.com>
 *   A detailled analysis of the mDNS issue can be found here:
 *   http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=736641
 *
 */
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <sys/types.h>
#include <libnet.h>
#include <string.h>
#include <arpa/inet.h>

#define MCAST_ALL_HOSTS "224.0.0.1"
#define INTERVAL_SECS   60

void rebuild_packet(libnet_t *l) {
    u_int32_t ip_addr, ip_dest_addr;

    // Destination IP addresses
    //ip_addr = libnet_name2addr4(l, MCAST_ALL_HOSTS, LIBNET_DONT_RESOLVE);
    //ip_dest_addr = libnet_name2addr4(l, "0.0.0.0", LIBNET_DONT_RESOLVE);
    ip_addr = 0xe0000001;
    ip_dest_addr = 0x00000000;

    /* Build IGMP packet */
    if(libnet_build_igmp(IGMP_MEMBERSHIP_QUERY,        // packet type
                         0,                            // packet code
                         0,                            // checksum (autofill)
                         0,                            // ipv4 address
                         NULL,                         // payload
                         0,                            // payload length
                         l,                            // context
                         0) == -1) {                   // protocol tag
        fprintf(stderr, "Error building IGMP packet: %s\n", libnet_geterror(l));
        libnet_destroy(l);
        exit(EXIT_FAILURE);
    }

    /* Build IP header */
    // Generate random id
    u_int16_t id = libnet_get_prand(LIBNET_PR16);
    if(libnet_build_ipv4(LIBNET_IPV4_H + LIBNET_IGMP_H,  // IP packet length
                         0,                              // tos
                         id,                             // id
                         0,                              // fragmentation bit
                         1,                              // ttl
                         IPPROTO_IGMP,                   // protocol
                         0,                              // checksum (autofill)
                         0,                              // source addr
                         ip_addr,                        // destination addr
                         NULL,                           // payload
                         0,                              // payload length
                         l,                              // context
                         0) == -1) {                     // protocol tag
        fprintf(stderr, "Error building IP header: %s\n", libnet_geterror(l));
        libnet_destroy(l);
        exit(EXIT_FAILURE);
    }
}

void do_igmp_query(libnet_t *l) {
    if (libnet_write(l) == -1)
        fprintf(stderr, "Error writing packet: %s\n", libnet_geterror(l));
}

int main(int argc, char *argv[]) {
    pid_t pid = 0, sid = 0;

    pid = fork();
    if (pid < 0) {
        fprintf(stderr, "Error: fork failed.\n");
        return -1;
    }

    if (pid > 0) {
        return 0; /* exit parent */
    }

    umask(0);

    sid = setsid();
    if (sid < 0) {
        fprintf(stderr, "Error: setsid failed.\n");
        return -1;
    }

    chdir("/");

    close(STDIN_FILENO);
    close(STDOUT_FILENO);
    close(STDERR_FILENO);

    /* Initialize libnet */
    libnet_t *l;
    char errbuf[LIBNET_ERRBUF_SIZE];
    char *device = NULL;

    if (argc > 1) {
        device = argv[1];
    }

    l = libnet_init(LIBNET_RAW4, device, errbuf);
    if (l == NULL) {
        fprintf(stderr, "libnet_init() failed: %s\n", errbuf);
        exit(EXIT_FAILURE);
    }

    libnet_seed_prand(l);

    /* main loop */
    while (1) {
        do_igmp_query(l);
        rebuild_packet(l);
        sleep(INTERVAL_SECS);
    }

    libnet_destroy(l);

    return 0;
}