#include <sys/types.h>
#include <sys/limits.h>
#include <sys/socket.h>

#include <arpa/inet.h>
#include <netinet/in.h>

#include <err.h>
#include <errno.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>

int
main (int argc, char **argv)
{
	int sock;
	struct in_addr group, if_addr;
	struct sockaddr_in bind_addr;
	struct ip_mreq mreq;


	memset(&bind_addr, 0, sizeof(struct sockaddr_in));

	if (argc == 1) {
		group.s_addr = htonl(INADDR_ALLHOSTS_GROUP);
		if_addr.s_addr = htonl(INADDR_LOOPBACK);
	} else if (argc == 3)  {
		if (inet_aton(argv[1], &group) != 1 ||
		    !IN_MULTICAST(ntohl(group.s_addr)))
			err(1, "Invalid group address - %s)", optarg);

		if (inet_aton (argv[2], &if_addr) != 1)
			err(1, "Invalid interface address - %s)", optarg);
	} else
		err(1, "<prog-name> [group-address] [interface-ip]");

	bind_addr.sin_family = AF_INET;
	bind_addr.sin_addr = group;

	if ((sock = socket (AF_INET, SOCK_DGRAM, IPPROTO_IP)) == -1)
		err(1, "socket failed");

	memset(&mreq, 0, sizeof (struct ip_mreq));
	mreq.imr_multiaddr = group;
	mreq.imr_interface = if_addr;

	if (setsockopt (sock, IPPROTO_IP, IP_ADD_MEMBERSHIP,
	    &mreq, sizeof(mreq)) < 0)
		err(1, "setsockopt() failed");

	if (setsockopt (sock, IPPROTO_IP, IP_ADD_MEMBERSHIP,
	    &mreq, sizeof(mreq)) < 0)
		err(1, "setsockopt() 2 failed");

	exit (0);
}