mc_socket.c

#include <stdio.h>
#include <unistd.h>
#include <netinet/igmp.h>
#include <linux/mroute.h>
#include <arpa/inet.h>

// socket configuration is based on https://github.com/pali/igmpproxy

int main() {

        int s = -1;
        int Va = 1;
        struct vifctl VifCtl;
        struct ip_mreqn mreq;

        // strace: socket(AF_INET, SOCK_RAW, IPPROTO_IGMP) = 3
        s = socket(AF_INET, SOCK_RAW, IPPROTO_IGMP);

        // strace: setsockopt(3, SOL_IP, 0xc8 /* IP_??? */, [1], 4) = 0
        setsockopt(s, IPPROTO_IP, MRT_INIT,(void *)&Va, sizeof( Va ));

        /*
        * root@mr3:~# ip a sh dev ens4
        * 4: ens4: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UP group default qlen 1000
        *     link/ether 52:54:00:13:97:a2 brd ff:ff:ff:ff:ff:ff
        *     inet 10.0.2.1/24 brd 10.0.2.255 scope global ens4
        *        valid_lft forever preferred_lft forever
        * root@mr3:~#
        */

        VifCtl.vifc_vifi = 1;
        VifCtl.vifc_flags = VIFF_USE_IFINDEX;
        VifCtl.vifc_lcl_ifindex = 4;
        VifCtl.vifc_lcl_addr.s_addr = 0x4;
        VifCtl.vifc_rmt_addr.s_addr = INADDR_ANY;
        VifCtl.vifc_threshold = 1;
        VifCtl.vifc_rate_limit = 0;

        // strace: setsockopt(3, SOL_IP, 0xca /* IP_??? */, "\1\0\10\1\0\0\0\0\4\0\0\0\0\0\0\0", 16) = 0
        setsockopt(s, IPPROTO_IP, MRT_ADD_VIF, (char *)&VifCtl, sizeof( VifCtl ));


        mreq.imr_multiaddr.s_addr = inet_addr("224.0.0.2");
        mreq.imr_address.s_addr = inet_addr("10.0.2.1");

        // strace: setsockopt(3, SOL_IP, IP_ADD_MEMBERSHIP, {imr_multiaddr=inet_addr("224.0.0.2"), imr_interface=inet_addr("10.0.2.1")}, 12) = 0
        setsockopt(s, IPPROTO_IP, IP_ADD_MEMBERSHIP,(char *)&mreq, sizeof(mreq));

        printf("sleeping for 30s..\n");
        sleep(30);

        close(s);
}