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

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

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

static void
usage(const char *cmd)
{
        fprintf(stderr,
            "%s -m addr -p port [-d dst] [-i addr] [-D delay]\n", cmd);
        exit(1);
}

int
main(int argc, char *argv[])
{
        struct ip_mreq mreq;
        struct sockaddr_in in, dst;
        struct in_addr iface;
        int s, opt, n, delay;

        memset(&in, 0, sizeof(in));
        in.sin_family = AF_INET;

        memset(&dst, 0, sizeof(dst));
        dst.sin_family = AF_INET;

        memset(&iface, 0, sizeof(iface));
        delay = 0;

        while ((opt = getopt(argc, argv, "m:p:d:i:D:")) != -1) {
                switch (opt) {
                case 'm':
                        if (inet_pton(AF_INET, optarg, &in.sin_addr) <= 0) {
                                fprintf(stderr, "invalid -m addr %s\n", optarg);
                                exit(1);
                        }
                        break;

                case 'p':
                        in.sin_port = htons(atoi(optarg));
                        dst.sin_port = in.sin_port;
                        break;

                case 'd':
                        if (inet_pton(AF_INET, optarg, &dst.sin_addr) <= 0) {
                                fprintf(stderr, "invalid -d addr %s\n", optarg);
                                exit(1);
                        }
                        break;

                case 'i':
                        if (inet_pton(AF_INET, optarg, &iface) <= 0) {
                                fprintf(stderr, "invalid -i addr %s\n", optarg);
                                exit(1);
                        }
                        break;

                case 'D':
                        delay = atoi(optarg);
                        break;

                default:
                        usage(argv[0]);
                }
        }

        if (in.sin_addr.s_addr == INADDR_ANY || in.sin_port == 0)
                usage(argv[0]);
        if (dst.sin_addr.s_addr == 0)
                dst.sin_addr = in.sin_addr;

        s = socket(AF_INET, SOCK_DGRAM, 0);
        if (s < 0) {
                fprintf(stderr, "socket failed: %d\n", errno);
                exit(1);
        }

        if (bind(s, (const struct sockaddr *)&in, sizeof(in)) < 0) {
                fprintf(stderr, "bind failed: %d\n", errno);
                exit(1);
        }

        memset(&mreq, 0, sizeof(mreq));
        mreq.imr_multiaddr = in.sin_addr;
        mreq.imr_interface = iface;
        if (setsockopt(s, IPPROTO_IP, IP_ADD_MEMBERSHIP,
            &mreq, sizeof(mreq)) < 0) {
                fprintf(stderr, "setsockopt IP MEMSHIP failed: %d\n", errno);
                exit(1);
        }

        if (iface.s_addr != INADDR_ANY) {
                if (setsockopt(s, IPPROTO_IP, IP_MULTICAST_IF,
                    &iface, sizeof(iface)) < 0) {
                        fprintf(stderr, "setsockopt IP IF failed: %d\n", errno);
                        exit(1);
                }
        }

        if (delay > 0)
                sleep(delay);

        n = sendto(s, &mreq, sizeof(mreq), 0,
            (const struct sockaddr *)&dst, sizeof(dst));
        if (n < 0) {
                fprintf(stderr, "sendto failed: %d\n", errno);
                exit(1);
        }

        exit(0);
}