#include <stdlib.h>
#include <string.h>
#include <stdio.h>
#include <sys/socket.h>
#include <arpa/inet.h>
#include <net/if.h>

void usage(void)
{
	printf(" --- Join a Multicast Group ---\n");
	printf("Usage:\n");
	printf("mjoin <interfarce> <group>\n");
	printf("example:"
		" host1# ./mjoin eth0 224.1.0.37\n"
		" host1# netstat -g\n"
		" host2# ping -r -I eth0 -t 1 -c 2 224.1.0.37\n");
	return;
}

int main(int argc, char *argv[])
{
	struct ip_mreqn mreqn;
	int fd, ret;

	if (argc != 3) {
		usage();
		exit(1);
	}
	/* Check arguments */
	memset(&mreqn, 0, sizeof(mreqn));
	mreqn.imr_ifindex = if_nametoindex(argv[1]);
	if (!mreqn.imr_ifindex){
		printf("Error: invalid interface\n");
		usage();
		exit(1);
	}
	ret = inet_pton(AF_INET, argv[2], &mreqn.imr_multiaddr);
	if (ret == 0) {
		printf("Error: not valid network address\n");
		usage();
		exit(1);
	}

	if (ret < 0) {
		printf("Error: not valid address family\n");
		usage();
		exit(1);
	}
	/* create a socket */
	if ((fd = socket(AF_INET, SOCK_DGRAM, 0)) < 0) {
		perror("socket");
		exit(1);
	}
	/* use setsockopt() to request that the kernel join a multicast group */
	if (setsockopt
	    (fd, IPPROTO_IP, IP_ADD_MEMBERSHIP, &mreqn, sizeof(mreqn)) < 0) {
		perror("setsockopt");
		exit(1);
	}
	getchar();
	exit(0);
}