/*
 * multisend.c
 *
 * This program transmits a single multicast datagram on a specified
 * IP multicast group and port. Its one special feature is that it lets
 * you choose a given interface on which to transmit the packet, which
 * is necessary if you have a multi-homed host.
 *
 * compile with: cc -o multisend multisend.c
 */

#include <sys/types.h>
#include <sys/socket.h>
#include <sys/sockio.h>
#include <netinet/in.h>
#include <net/if.h>

#include <stdio.h>
#include <errno.h>
#ifdef __FreeBSD__
#include <err.h>
#else
#define err(x, y) \
	{			\
		perror(y);	\
		exit(x);	\
	}
#endif
#include <stdlib.h>
#include <unistd.h>
#include <string.h>

main()
{
	struct ip_mreq		mreq;
	struct ifreq		ifreq;
	int			sock;
	char			buf[] = "This is a test";
	struct sockaddr_in	sin;

	bzero((char *)&ifreq, sizeof(ifreq));
	bzero((char *)&mreq, sizeof(mreq));
	bzero((char *)&sin, sizeof(sin));

	/* Specify the multicast group and port you want to use here */
	sin.sin_addr.s_addr = inet_addr("224.2.100.100");
	sin.sin_port = htons(12345);
	sin.sin_family = AF_INET;

	mreq.imr_multiaddr.s_addr = sin.sin_addr.s_addr;

	/* Create socket. */
	sock = socket(AF_INET, SOCK_DGRAM, 0);
	if (sock == -1)
		err(1, "socket failed");

	/* Specify the interface you want to use here. */
	strcpy(ifreq.ifr_name, "vr0");

	/* Get interface info. */
	if (ioctl(sock, SIOCGIFADDR, &ifreq) == -1)
		err(1, "ioctl failed");

	bcopy((char *)&((struct sockaddr_in *)&ifreq.ifr_addr)->sin_addr,
		(char *)&mreq.imr_interface, sizeof(struct in_addr));

	/* Join the multicast group. */
	if (setsockopt(sock, IPPROTO_IP, IP_ADD_MEMBERSHIP,
		(void *)&mreq, sizeof(mreq)) == -1)
		err(1, "join failed");

	/* Select the interface. */
	if (setsockopt(sock, IPPROTO_IP, IP_MULTICAST_IF,
		(void *)&mreq.imr_interface, sizeof(struct in_addr)) == -1)
		err(1, "set interface failed");

	/* Transmit the datagram. */
	if (sendto(sock, buf, strlen(buf), 0, (struct sockaddr *)&sin,
		sizeof(sin)) == -1)
		err(1, "sendto failed");

	close(sock);

	exit(0);
}