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

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

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

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

int
main(int argc, char *argv[])
{
        struct sockaddr_in dst, local_in;
        struct in_addr iface, mcast_if;
        int s, opt, n, loop = 0, use_mreq = 0, iface_idx;
        uint8_t buf[18];
        socklen_t mcast_if_len;
        char mcast_if_str[INET_ADDRSTRLEN];

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

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

        memset(&iface, 0, sizeof(iface));
        iface_idx = -1;

        while ((opt = getopt(argc, argv, "I:P:d:i:mp:")) != -1) {
                switch (opt) {
                case 'I':
                        iface_idx = if_nametoindex(optarg);
                        break;

                case 'P':
                        local_in.sin_port = strtol(optarg, NULL, 10);
                        local_in.sin_port = htons(local_in.sin_port);
                        break;

                case 'd':
                        if (inet_pton(AF_INET, optarg, &dst.sin_addr) <= 0)
                                usage(argv[0]);
                        break;

                case 'i':
                        if (inet_pton(AF_INET, optarg, &iface) <= 0)
                                usage(argv[0]);
                        break;

                case 'm':
                        use_mreq = 1;
                        break;

                case 'p':
                        dst.sin_port = strtol(optarg, NULL, 10);
                        dst.sin_port = htons(dst.sin_port);
                        break;

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

        if ((iface.s_addr == INADDR_ANY && iface_idx < 0) ||
            dst.sin_addr.s_addr == INADDR_ANY || dst.sin_port == 0)
                usage(argv[0]);

        s = socket(AF_INET, SOCK_DGRAM, 0);
        if (s < 0)
                err(2, "socket failed");

        if (iface_idx >= 0) {
                struct ip_mreqn mreqn;

                fprintf(stderr, "ip_mreqn mcast_if ifindex %d\n", iface_idx);
                memset(&mreqn, 0, sizeof(mreqn));
                mreqn.imr_address = iface;
                mreqn.imr_ifindex = iface_idx;
                if (setsockopt(s, IPPROTO_IP, IP_MULTICAST_IF,
                    &mreqn, sizeof(mreqn)) < 0)
                        err(2, "setsockopt IP_MULTICAST_IF ip_mreqn failed");
        } else if (use_mreq) {
                struct ip_mreq mreq;

                fprintf(stderr, "ip_mreq mcast_if\n");
                memset(&mreq, 0, sizeof(mreq));
                mreq.imr_interface = iface;
                if (setsockopt(s, IPPROTO_IP, IP_MULTICAST_IF,
                    &mreq, sizeof(mreq)) < 0)
                        err(2, "setsockopt IP_MULTICAST_IF ip_mreq failed");
        } else {
                if (setsockopt(s, IPPROTO_IP, IP_MULTICAST_IF,
                    &iface, sizeof(iface)) < 0)
                        err(2, "setsockopt IP_MULTICAST_IF inaddr failed");
        }

        mcast_if_len = sizeof(mcast_if);
        if (getsockopt(s, IPPROTO_IP, IP_MULTICAST_IF,
            &mcast_if, &mcast_if_len) < 0)
                err(2, "getsockopt IP_MULTICAST_IF failed");
        fprintf(stderr, "ifindex %s\n", inet_ntop(AF_INET, &mcast_if,
            mcast_if_str, sizeof(mcast_if_str)));

        if (setsockopt(s, IPPROTO_IP, IP_MULTICAST_LOOP,
            &loop, sizeof(loop)) < 0)
                err(2, "setsockopt IP_MULTICAST_LOOP failed");

        if (local_in.sin_port != 0) {
                local_in.sin_addr = iface;
                if (bind(s, (const struct sockaddr *)&local_in,
                    sizeof(local_in)) < 0)
                        err(2, "bind failed");
        }

        n = sendto(s, buf, sizeof(buf), 0,
            (const struct sockaddr *)&dst, sizeof(dst));
        if (n < 0)
                err(2, "sendto failed");
        else if (n < (int)sizeof(buf))
                errx(2, "sent truncated data %d", n);

        exit(0);
}