nng_receiver.cpp

//
// Created by Johannes Mey on 26.05.20.
//

#include "ros/ros.h"

#include <sstream>

#include <nng/nng.h>
#include <nng/protocol/pubsub0/sub.h>
#include <std_msgs/String.h>

std::string url = "tcp://localhost:6576";

int main(int argc, char **argv) {
  ros::init(argc, argv, "nng_receiver");

  ros::NodeHandle n("nnc_test");

  ros::Publisher nng_receiver_pub = n.advertise<std_msgs::String>("received_nng", 1000);

  ros::Rate loop_rate(200);

  nng_socket sock;
  int rv;

  if ((rv = nng_sub0_open(&sock)) != 0) {
    ROS_ERROR_STREAM("nng_sub0_open returned: " << nng_strerror(rv));
  }

  // subscribe to everything (empty means all topics)
  if ((rv = nng_setopt(sock, NNG_OPT_SUB_SUBSCRIBE, "", 0)) != 0) {
    ROS_ERROR_STREAM("nng_setopt returned: " << nng_strerror(rv));
  }
  if ((rv = nng_dial(sock, url.c_str(), nullptr, 0)) != 0) {
    ROS_ERROR_STREAM("nng_dial returned: " << nng_strerror(rv));
  }

  while (ros::ok()) {

    char *buf = nullptr;
    size_t sz;
    if ((rv = nng_recv(sock, &buf, &sz, NNG_FLAG_ALLOC | NNG_FLAG_NONBLOCK)) == 0) {

      // store the result in a string and free the buffer
      std::string result(buf, sz);
      nng_free(buf, sz);

      ROS_INFO_STREAM("CLIENT: RECEIVED '" << result << "'");

      // build and publish a ROS message
      std_msgs::String msg;
      msg.data = result;
      ROS_INFO_STREAM("Publishing ROS message '" << msg.data << "'");
      nng_receiver_pub.publish(msg);
    } else if (rv == NNG_EAGAIN) {
      // no message received in current spin
    } else {
      ROS_ERROR_STREAM("nng_recv returned: " << nng_strerror(rv));
    }

    ros::spinOnce();

    loop_rate.sleep();
  }


  return 0;
}