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

#include <arpa/inet.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 -m addr -p port -i addr "
            "-r remote_ip4 -P remote_port\n", cmd);
        exit(1);
}

static int
create_sock(const struct sockaddr_in *in, const struct in_addr *iface)
{
        struct ip_mreq mreq;
        int s, on;

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

        on = 1;
        if (setsockopt(s, SOL_SOCKET, SO_REUSEPORT, &on, sizeof(on)) < 0)
                err(2, "setsockopt SO_REUSEPORT failed");

        if (bind(s, (const struct sockaddr *)in, sizeof(*in)) < 0)
                err(2, "bind failed");

        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)
                err(2, "setsockopt IP_ADD_MEMBERSHIP failed");

        return s;
}

int
main(int argc, char *argv[])
{
        struct sockaddr_in in, remote_in;
        struct in_addr iface;
        int s1, s2, opt, n;
        uint8_t buf[18];

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

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

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

        while ((opt = getopt(argc, argv, "P:i:m:p:r:")) != -1) {
                switch (opt) {
                case 'P':
                        remote_in.sin_port = strtol(optarg, NULL, 10);
                        remote_in.sin_port = htons(remote_in.sin_port);
                        break;

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

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

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

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

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

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

        s1 = create_sock(&in, &iface);
        s2 = create_sock(&in, &iface);

        if (connect(s2, (const struct sockaddr *)&remote_in,
            sizeof(remote_in)) < 0)
                err(2, "connect failed");

        n = read(s1, buf, sizeof(buf));
        if (n < 0)
                err(2, "read 1 failed");
        fprintf(stderr, "read 1 got %d\n", n);

        n = read(s2, buf, sizeof(buf));
        if (n < 0)
                err(2, "read 2 failed");
        fprintf(stderr, "read 2 got %d\n", n);

        exit(0);
}