Communicate using json string with ZMQ

client.cpp

#include <zmq.hpp>
#include <string>
#include <iostream>
#include "json.hpp"

int main() {
  zmq::context_t context;
  zmq::socket_t socket(context, ZMQ_REQ);
  socket.connect("tcp://localhost:5555");
  for (int i = 0; i < 10; ++i) {
    nlohmann::json request;
    request["a"] = 123;
    std::string json_str = request.dump();
    
    zmq::message_t query(json_str.length());
    memcpy(query.data(), (json_str.c_str()), (json_str.size()));
    socket.send(query);

    zmq::message_t reply;
    socket.recv(reply);
    auto reply_str = std::string(static_cast<char *>(reply.data()), reply.size());
    std::cout << reply_str << std::endl;

    auto reply_json = nlohmann::json::parse(reply_str);
    std::cout << reply_json["a"] << " " << int(reply_json["a"]) << std::endl;
  }
}

server.py

import zmq
import time
context = zmq.Context()
socket = context.socket(zmq.REP)
socket.bind("tcp://0.0.0.0:5555")

while True:
    #  Wait for next request from client
    message = socket.recv_json()
    print("Received request: ", message)
    time.sleep(1)
    ret = {"a": 123, "b": 321}
    socket.send_json(ret)