How to send the message between two nodes correctly in OMNeT++

Question

I am new to OMNeT++ and I do not have much experience in C++. In my OMNeT++ scenario I have two nodes (coming from SUMO scenario). I want to send a node_indicator from Python (in this case it is 0), then send some message from node 0 to node 1 and return that message back to Python. I am trying to achieve this with the following code:

Define_Module(veins::TraCIDemo11p);

void TraCIDemo11p::initialize(int stage)
{
    DemoBaseApplLayer::initialize(stage);
    if (stage == 0) {
        sentMessage = false;
        lastDroveAt = simTime();
        currentSubscribedServiceId = -1;

    }
    this->communicate_with_python();
}

void TraCIDemo11p::communicate_with_python() {

    //  Prepare our context and socket
    zmq::context_t context(1);
    zmq::socket_t socket(context, ZMQ_REP);
    socket.bind("tcp://*:5555");

    zmq::message_t request;
    //  Wait for next request from client
    socket.recv(request);
    std::string requestMessage = std::string(static_cast<char *>(request.data()), request.size());
    // Print out received message
    EV << "Received from Python: " + requestMessage << std::endl;  //requestMessage = 0

    std::string msgToClient(" ");
    this->message_exchange(stoi(requestMessage));

    //  Send reply back to client
    msgToClient = message_to_python;
    EV << "Returning Message back to Python" << "\n";
    socket.send(zmq::message_t(msgToClient.data(), msgToClient.size()), zmq::send_flags::none);
}

void TraCIDemo11p::message_exchange(int node_indicator) {
    // Send the message from node 0 to node 1
        if (findHost()->getIndex()==node_indicator) {
            sentMessage=true;
            TraCIDemo11pMessage* wsm = new TraCIDemo11pMessage();
            populateWSM(wsm);

            std::string message = "Message from node 0 to node 1";

            wsm->setDemoData(message.c_str());
            EV << "Sending Now!" << "\n";
            sendDown(wsm);
    }
}

void TraCIDemo11p::onWSM(BaseFrame1609_4* frame)
{
    TraCIDemo11pMessage* wsm = check_and_cast<TraCIDemo11pMessage*>(frame);

    EV << "Message from node 0 received! " << wsm->getDemoData() << " on node " << findHost()->getFullName() << "\n";
    if (strcmp("0", python_request.c_str()) == 0) {
        message_to_python = wsm->getDemoData();
        EV << "Assigned Message to Python!" << "\n";
    }

It does not work. In Python only '' gets returned. My problem is that I do not understand in which sequence the compiler evaluates the statements. I expect the following sequence

• Method communicate_with_python
  • Receive the node indicator from Python
• Method message_exchange
  • Node 0 sends the message to node 1
• Method onWSM
  • Node 1 receives the message from node 0 and saves it to message_to_python variable
• Method communicate_with_python
  • Assigns the traversed message to msgToClient and sends it to Python

In reality, I get the following outputs at my console

...
INFO (TraCIDemo11p)RSUExampleScenario.node[1].appl:Received from Python: 0
INFO (TraCIDemo11p)RSUExampleScenario.node[1].appl:Returning Message back to Python
...
INFO:Message from node 0 received! Message from node 0 to node 1 on node node[1]
...
INFO:Message from node 0 received! Message from node 0 to node 1 on node node[1]
...

Could somebody explain to me how the methods are called inside my class? And also how do I implement it correctly.

Thank you!

Answer 1

Have you tried it the conventional way as given in TraciDemo11p example. Can you please explain the need of using sockets here. Thanks