Receiving 0 size messages while using ZMQ and prot

Question

I am trying to set up a basic communication system between client and server using ZMQ. I am using protobuf for the message format. My problem is when I send the message from client the message size is 34 but the message size received on the server is 0.

Following is my code;

Client.cpp

tutorial::Person person;
person.set_id(1234);
person.set_name("john");
person.set_email("[e-mail]");
person.set_phonenumber("12345678");


zmq::context_t context (1); //  Prepare our context and socket
zmq::socket_t socket (context, ZMQ_PAIR);

std::cout << "Connecting to server…" << std::endl;
int linger = 0;// ms
socket.setsockopt(ZMQ_LINGER, &linger, sizeof(linger));
socket.connect ("tcp://127.0.0.1:20000");

std::string msg_str;
person.SerializeToString(&msg_str);
std::cout << "Size of message string is "<< msg_str.size()<<std::endl;
zmq::message_t request (msg_str.size());
memcpy ((void *) request.data (), msg_str.c_str(), msg_str.size());
std::cout << "Sending Person data ..." << std::endl;
socket.send (request);

socket.close();

google::protobuf::ShutdownProtobufLibrary();
return 0;

Server.cpp :

zmq::context_t context(1); //  Prepare our context and socket
zmq::socket_t socket(context, ZMQ_PAIR);
int linger = 0; // ms
socket.setsockopt(ZMQ_LINGER, &linger, sizeof(linger));
socket.bind("tcp://127.0.0.1:20000");
while (true)
 {
    zmq::message_t request;
    int recieved = socket.recv(&request);
    std::string msg(static_cast<char*>(request.data()),request.size());
    std::cout<<"Size of message recieved is "<<  msg.size()<<std::endl;
    tutorial::Person person;
    person.ParseFromString(msg);
    std::string text_str1;
    google::protobuf::TextFormat::PrintToString(person, &text_str1);
}
socket.close();

Output of Client is :

Size of message string is 34

Output of server is :

Size of message received is 0

I have tried tried switching to ParseToArray also but it did not help. Any kind of help is appreciated.

Answer 1

I have solved it with another way. Actually earlier I installed libzmq lib , but later when I switched to libzmq3-dev it worked for me.

Answer 2

I had the exact same problem; what I found is that the zmq::message_t had to go out of scope OR rebuild needed to be called.

For example, if the publisher looked like this.

        zmq::message_t msg(3);
        memcpy(msg.data(), "abc", 3);
        while (1 == 1) {
            pubSocket.send(msg);
            sleep(1);
        }

The subscriber would receive messages of zero length. If the code was changed to

        while (1 == 1) {
            zmq::message_t msg(3);
            memcpy(msg.data(), "abc", 3);

            pubSocket.send(msg);
            sleep(1);
        }

OR

        zmq::message_t msg(3);
        memcpy(msg.data(), "abc", 3);
        while (1 == 1) {
            pubSocket.send(msg);
            msg.rebuild(3);
            sleep(1);
        }

Then the subscriber would receive a 3-byte message.