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

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

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

static void
usage(const char *cmd)
{
        fprintf(stderr, "%s -4 ip4 -p port\n", cmd);
        exit(1);
}

int
main(int argc, char *argv[])
{
        struct sockaddr_in in, in2;
        int s, opt, n;
        uint8_t buf[18];

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

        while ((opt = getopt(argc, argv, "4:p:")) != -1) {
                switch (opt) {
                case '4':
                        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;

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

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

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

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

        memset(&in2, 0, sizeof(in2));
        in2.sin_family = AF_UNSPEC;
        connect(s, (const struct sockaddr *)&in2, sizeof(in2));

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

        n = read(s, buf, sizeof(buf));
        if (n < 0)
                err(2, "read failed");
        printf("read %d, done\n", n);

        exit(0);
}