#include <stdio.h>
#include <time.h>
#include <poll.h>
#include <assert.h>
#include <string.h>

#include <arpa/inet.h>
#include <netdb.h>
#include <netinet/in.h>
#include <sys/socket.h>
#include <sys/socket.h>
#include <sys/types.h>

static void dump(const char *s, size_t len) {
    while (len--) {
        char t = *s++;
        if (' ' <= t && t <= '~' && t != '\\')
            printf("%c", t);
        else
            printf("\\%o", t & 0xff);
    }
    printf("\n");
}

int main(int argc, char *argv[]) {
    int sock, rv, n;
    const char req[] =
        "\202\254\1\0\0\1\0\0\0\0\0\0\7example\3com\0\0\1\0\1";
    struct timespec delay_l = { 1, 0 }; /* 1 sec */
    struct pollfd pfs;
    struct sockaddr_in me = { 0 };

    sock = socket(AF_INET, SOCK_DGRAM | SOCK_CLOEXEC | SOCK_NONBLOCK,
                  IPPROTO_IP);
    assert(sock >= 0);

    me.sin_family = AF_INET;
    me.sin_port = 0;
    me.sin_addr.s_addr = inet_addr("0.0.0.0");
    rv = bind(sock, (struct sockaddr *) &me, sizeof me);
    assert(0 == rv);

    for (n = 1; n < argc; n++) {
        if (0 == strcmp("delay", argv[n])) {
            struct timespec delay_s = { 0, (1 << 24) }; /* ~ 16 msec */
            nanosleep(&delay_s, NULL);
        } else {
            struct sockaddr_in dst = { 0 };
            dst.sin_family = AF_INET;
            dst.sin_port = htons(53);
            dst.sin_addr.s_addr = inet_addr(argv[n]);
            rv = sendto(sock, req, sizeof req - 1, MSG_NOSIGNAL,
                        (struct sockaddr *) &dst, sizeof dst);
            assert(rv >= 0);
        }
    }

    nanosleep(&delay_l, NULL);
    pfs.fd = sock;
    pfs.events = POLLIN;
    rv = poll(&pfs, 1, 2000);
    printf("poll: %d %d %d\n", rv, pfs.events, pfs.revents);

    for (n = 1; n < argc; n++) {
        char resp[4000];
        if (0 == strcmp("delay", argv[n]))
            continue;
        rv = recvfrom(sock, resp, sizeof resp, 0, NULL, NULL);
        printf("recvfrom() %d\n", rv);
        if (rv > 0)
            dump(resp, rv);
    }

    return 0;
}