ZeroMQ's EPGM not working in weather PUB-SUB demo

Question

I have compiled libzmq with openpgm with no changes under windows. Code here is taken from ZeroMQ Guide ("weather publisher" server/client). But if i change "tcp" to "epgm" it doesn't work any more (data is not received, but connection is established).

void test_serv()
{    
    //  Prepare our context and publisher
    void *context = zmq_ctx_new();
    void *publisher = zmq_socket(context, ZMQ_PUB);
    int rc = zmq_bind(publisher, "epgm://127.0.0.1:5556");
    assert(rc == 0);

    //  Initialize random number generator
    srandom((unsigned)time(NULL));
    while (!stop_server)
    {
        //  Get values that will fool the boss
        int zipcode, temperature, relhumidity;
        zipcode = randof(1000) + 600;
        temperature = randof(215) - 80;
        relhumidity = randof(50) + 10;

        //  Send message to all subscribers
        char update[20];
        sprintf(update, "%d %d %d", zipcode, temperature, relhumidity);
        s_send(publisher, update);
    }
    LOG("END Server shutdown");
    Sleep(500);
    zmq_close(publisher);
    zmq_ctx_destroy(context);
}

void test_sock()
{    
    //  Socket to talk to server
    LOG("Collecting updates from weather server...");
    void *context = zmq_ctx_new();
    void *subscriber = zmq_socket(context, ZMQ_SUB);
    int rc = zmq_connect(subscriber, "epgm://127.0.0.1:5556");
    assert(rc == 0);

    //  Subscribe to zipcode, default is NYC, 10001
    char *filter = "1001 ";
    rc = zmq_setsockopt(subscriber, ZMQ_SUBSCRIBE,
        filter, strlen(filter));
    assert(rc == 0);

    //  Process 100 updates
    int update_nbr;
    long total_temp = 0;
    for (update_nbr = 0; update_nbr < 10; update_nbr++) {
        char *string = s_recv(subscriber);

        int zipcode, temperature, relhumidity;
        sscanf(string, "%d %d %d",
            &zipcode, &temperature, &relhumidity);
        total_temp += temperature;
        LOG(">> " << string);
        free(string);
    }
    LOG("Average temperature for zipcode "<< filter << "was " << (int)(total_temp / update_nbr) << 'F');

    zmq_close(subscriber);
    zmq_ctx_destroy(context);
}

I run two functions in different threads, with tcp anything works as expected.

I have tried doing "route print 0.0.0.0" with cmd.exe and using interface IP (192.168.137.64) as prefix instead of "eth0" like shown in RFC: epgm://192.168.137.64;127.0.0.1:5556 on connect and/or bind, but this brokes my socket and raises error.

Also "PGM" requires administrator rights and i cannot test it now.

The error IS NOT "protocol not supported" errno is set to B (11) and i don't understand what does it mean (no docs on it).

Answer 1

EPGM is a bit finicky. According to this list post, if you're using EPGM your publisher and subscriber must be on separate hosts. More details here, it looks like this was a deliberate choice by the ZMQ team.

So, try it by spinning up your PUB and SUB on separate machines (changing the network addresses accordingly, of course).