text: #include <stdbool.h>
  #include <stdio.h>
  #include <stdlib.h>
  #include <string.h>
  #include <mosquitto.h>
  #include <mqtt_protocol.h>
  
  static int run = -1;
  static int sent_mid = -1;
  
  void on_connect(struct mosquitto *mosq, void *obj, int rc)
  {
  	if(rc){
  		exit(1);
  	}else{
  		mosquitto_subscribe(mosq, NULL, "response/topic", 0);
  	}
  }
  
  void on_subscribe(struct mosquitto *mosq, void *obj, int mid, int qos_count, const int *granted_qos)
  {
  	mosquitto_property *props = NULL;
  	mosquitto_property_add_string(&props, MQTT_PROP_RESPONSE_TOPIC, "response/topic");
  	mosquitto_property_add_binary(&props, MQTT_PROP_CORRELATION_DATA, "corridor", 8);
  	mosquitto_publish_v5(mosq, NULL, "request/topic", 6, "action", 0, 0, props);
  	mosquitto_property_free_all(&props);
  }
  
  void on_message(struct mosquitto *mosq, void *obj, const struct mosquitto_message *msg)
  {
  	if(!strcmp(msg->payload, "a response")){
  		run = 0;
  	}else{
  		run = 1;
  	}
  }
  
  int main(int argc, char *argv[])
  {
  	int rc;
  	struct mosquitto *mosq;
  	int ver = PROTOCOL_VERSION_v5;
  
  	int port = atoi(argv[1]);
  
  	mosquitto_lib_init();
  
  	mosq = mosquitto_new("request-test", true, NULL);
  	mosquitto_opts_set(mosq, MOSQ_OPT_PROTOCOL_VERSION, &ver);
  	mosquitto_connect_callback_set(mosq, on_connect);
  	mosquitto_subscribe_callback_set(mosq, on_subscribe);
  	mosquitto_message_callback_set(mosq, on_message);
  
  	rc = mosquitto_connect(mosq, "localhost", port, 60);
  
  	while(run == -1){
  		rc = mosquitto_loop(mosq, -1, 1);
  	}
  
  	mosquitto_lib_cleanup();
  	return run;
  }
  