ZeroMQ

A High-Level API for ØMQ

We’re going to push request-reply onto the stack now and open a different area, which is the ØMQ API itself. There’s a reason for this detour: as we write more complex examples, the low-level ØMQ API starts to look increasingly clumsy. Look at the core of the worker thread from our load-balancing broker:

while (true) {
    //  Read and save all frames until we get an empty frame
    //  In this example there is only 1 but there could be more
    char *address = s_recv (worker);
    char *empty = s_recv (worker);
    assert (*empty == 0);
    free (empty);

    //  Get request, send reply
    char *request = s_recv (worker);
    printf ("Worker: %s\n", request);
    free (request);

    s_sendmore (worker, address);
    s_sendmore (worker, "");
    s_send     (worker, "OK");
    free (address);
}

That code isn’t even reusable because it can only handle one reply address in the envelope, and it already does some wrapping around the ØMQ API. If we used the libzmq API directly, this is what we’d have to write:

while (true) {
    //  Read and save all frames until we get an empty frame
    //  In this example there is only 1 but there could be more
    zmq_msg_t address;
    zmq_msg_init (&address);
    zmq_msg_recv (worker, &address, 0);

    zmq_msg_t empty;
    zmq_msg_init (&empty);
    zmq_msg_recv (worker, &empty, 0);

    //  Get request, send reply
    zmq_msg_t payload;
    zmq_msg_init (&payload);
    zmq_msg_recv (worker, &payload, 0);

    int char_nbr;
    printf ("Worker: ");
    for (char_nbr = 0; char_nbr < zmq_msg_size (&payload); char_nbr++)
        printf ("%c", *(char ...