Sending a message from a ROUTER socket to a specific DEALER socket by settings its ID

[vpaladino778]

I'm having an issue using cppzmq to send a message from a ROUTER to a DEALER using a prepended ID to route to the specific dealer. I've constructed a minimal example below:

router.cpp

#include <iostream>
#include <zmq.hpp>
#include <string>
#include <thread>
#include <chrono>

int main() {
    zmq::context_t context;
    zmq::socket_t socket (context, zmq::socket_type::router);
    socket.setsockopt(ZMQ_ROUTER_MANDATORY, 1);
    socket.bind("tcp://*:5555");
   getchar() ;  // Wait till we launch dealer.cpp, then we'll hit enter to send the message
    try {
        std::string jobRequest = "ExampleJobRequest";
        // Send JobRequest to camera to run
        std::cout << "Router: Sending msg: " << jobRequest << std::endl;

        // Set the address, then the empty delimiter and then the request itself
        socket.send("PEER2", ZMQ_SNDMORE);
        //socket.send(zmq::message_t(), ZMQ_SNDMORE);
        socket.send(zmq::str_buffer("ExampleJobRequest"));
        
        // Receive the reply from the camera
        std::cout << "Router: Waiting for reply from camera " << std::endl;
        zmq::message_t reply;
        socket.recv(&reply);

        std::cout << "Router: Received " <<  std::string(static_cast<char*>(reply.data()), reply.size()) << std::endl;
    } catch (std::exception e) {
        std::cout << "Router Error: " << e.what();
    }

    std::this_thread::sleep_for(std::chrono::seconds(1));
    //socket.setsockopt(ZMQ_LINGER, 0);
    socket.close();
    context.close();
}

dealer.cpp

int main (void)
{
    //  Prepare our context and socket
    zmq::context_t context;
    zmq::socket_t socket (context, zmq::socket_type::dealer);

    std::cout << "Dealer: Connecting to RunJob server… \n";
    // Identity of peer socket must be set before binding/connecting
    socket.setsockopt(ZMQ_IDENTITY, "PEER2", 5);
    socket.connect ("tcp://localhost:5555");

    while(true) {
        try {
            // Wait for next request from client
            std::cout << "Dealer: Waiting for request" << std::endl;
            zmq::message_t request;
            zmq::message_t empty;

            // Receive request
            socket.recv(&request);

            std::string requestString = std::string(static_cast<char*>(request.data()), request.size());

            std::cout << "Dealer: Received request" << std::endl;
            std::cout << requestString << std::endl;

            socket.send(zmq::str_buffer("Job completed"), zmq::send_flags::dontwait);
        }catch (std::exception e) {
            std::cout << "Router Error: " << e.what();
        }
    }

    // Used to set various 0MQ Socket Settings
    // ZMQ_Linger - Set linger period for socket shutdown
    socket.setsockopt(ZMQ_LINGER, 0);
    socket.close();
    context.close();

    return 0;
}

After executing these two programs, they both hang on the recv calls. I have search extensively for the cause of this solution. I've also outlines this issue in a stackoverflow post. It appears that the message that the ROUTER is sending to the DEALER is getting lost, and not sent correctly.

[vpaladino778]

Here are some examples of ways i've tried sending messages (Prepended with the ID):

Example 1 - Resulted in crash in try/catch, 'unknown exception:

        socket.send("PEER2", ZMQ_SNDMORE);
        socket.send(zmq::message_t(), ZMQ_SNDMORE);
        socket.send(zmq::str_buffer("ExampleJobRequest"));

Example 2 - Same result as example 1:

        zmq::message_t empty(0);
        socket.send("PEER2", ZMQ_SNDMORE);
        socket.send(empty, ZMQ_SNDMORE);
        socket.send(zmq::str_buffer("ExampleJobRequest"));

Example 3 - No crash, but message never reaches DEALER:

        socket.send("PEER2", ZMQ_SNDMORE);
        socket.send(&zmq::message_t(), ZMQ_SNDMORE);
        socket.send(zmq::str_buffer("ExampleJobRequest"));

Example 4 - Same result as example 1:

        socket.send("PEER2", ZMQ_SNDMORE);
        socket.send(zmq::message_t(0), ZMQ_SNDMORE);
        socket.send(zmq::str_buffer("ExampleJobRequest"));

[gummif]

I suggest you use the new send and recv functions that take send_flags or recv_flags to avoid all kinds of bugs. I think for socket.send("PEER2", ZMQ_SNDMORE); you are setting the message size as ZMQ_SNDMORE.

See if that solves the problem you are having.

[getarobo]

@vpaladino778 Hey, I am trying achieve something similar and having similar issues. Were you able to get work this out?

[hyphenlee]

I solve this problem by:

            socket.send("A",1, ZMQ_SNDMORE);
            socket.send(zmq::str_buffer("ExampleJobRequest"));

[gummif]

Or

        socket.send(zmq::str_buffer("PEER2"), zmq::send_flags::sndmore);
        socket.send(zmq::message_t(), zmq::send_flags::sndmore);
        socket.send(zmq::str_buffer("ExampleJobRequest"));

or even

        std::array<zmq::const_buffer, 3> bufs = {
          zmq::str_buffer("PEER2"),
          zmq::str_buffer(""),
          zmq::str_buffer("ExampleJobRequest")
        };
        zmq::send_multipart(socket, bufs);

[chunyunzhe]

send(zmq::str_buffer(msg), ZMQ_SNDMORE) -> send(zmq::str_buffer(msg), strlen(msg), ZMQ_SNDMORE)