C++ Paho MQTT connection as a subscriber issue - c++

Question

I'm pretty new to C++ and was playing around with the Paho MQTT C++ client.
I've rearranged the sample async subscriber, but ran into an error of 'connection lost, cause: connect onSuccess called'. Spent hours trying to find the solution to no prevail.
My Main file:
int main()
{
subscriber();
return 0;
}
My header file: 'subscriber.hpp' ..has all the dependacy and mqtt/async_client.h
int subscriber();
My source file: subscriber.cpp
#include "subscriber.hpp"
const std::string SERVER_ADDRESS("tcp://localhost:1883");
const std::string CLIENT_ID("eclipse_subscriber");
const std::string TOPIC("topic2");
const int QOS = 1;
const int N_RETRY_ATTEMPTS = 5;
/////////////////////////////////////////////////////////////////////////////
// Callbacks for the success or failures of requested actions.
// This could be used to initiate further action, but here we just log the
// results to the console.
class action_listener : public virtual mqtt::iaction_listener
{
std::string name_;
void on_failure(const mqtt::token& tok) override {
std::cout << name_ << " failure";
if (tok.get_message_id() != 0)
std::cout << " for token: [" << tok.get_message_id() << "]" << std::endl;
std::cout << std::endl;
}
void on_success(const mqtt::token& tok) override {
std::cout << name_ << " success";
if (tok.get_message_id() != 0)
std::cout << " for token: [" << tok.get_message_id() << "]" << std::endl;
auto top = tok.get_topics();
if (top && !top->empty())
std::cout << "\ttoken topic: '" << (*top)[0] << "', ..." << std::endl;
std::cout << std::endl;
}
public:
action_listener(const std::string& name) : name_(name) {}
};
/////////////////////////////////////////////////////////////////////////////
/**
* Local callback & listener class for use with the client connection.
* This is primarily intended to receive messages, but it will also monitor
* the connection to the broker. If the connection is lost, it will attempt
* to restore the connection and re-subscribe to the topic.
*/
class callback : public virtual mqtt::callback,
public virtual mqtt::iaction_listener
{
// Counter for the number of connection retries
int nretry_;
// The MQTT client
mqtt::async_client& cli_;
// Options to use if we need to reconnect
mqtt::connect_options& connOpts_;
// An action listener to display the result of actions.
action_listener subListener_;
// This deomonstrates manually reconnecting to the broker by calling
// connect() again. This is a possibility for an application that keeps
// a copy of it's original connect_options, or if the app wants to
// reconnect with different options.
// Another way this can be done manually, if using the same options, is
// to just call the async_client::reconnect() method.
void reconnect() {
std::this_thread::sleep_for(std::chrono::milliseconds(2500));
try {
cli_.connect(connOpts_, nullptr, *this);
}
catch (const mqtt::exception& exc) {
std::cerr << "Error: " << exc.what() << std::endl;
exit(1);
}
}
// Re-connection failure
void on_failure(const mqtt::token& tok) override {
std::cout << "Connection attempt failed" << std::endl;
if (++nretry_ > N_RETRY_ATTEMPTS)
exit(1);
reconnect();
}
// (Re)connection success
// Either this or connected() can be used for callbacks.
void on_success(const mqtt::token& tok) override {}
// (Re)connection success
void connected(const std::string& cause) override {
std::cout << "\nConnection success" << std::endl;
std::cout << "\nSubscribing to topic '" << TOPIC << "'\n"
<< "\tfor client " << CLIENT_ID
<< " using QoS" << QOS << "\n"
<< "\nPress Q<Enter> to quit\n" << std::endl;
cli_.subscribe(TOPIC, QOS, nullptr, subListener_);
}
// Callback for when the connection is lost.
// This will initiate the attempt to manually reconnect.
void connection_lost(const std::string& cause) override {
std::cout << "\nConnection lost" << std::endl;
if (!cause.empty())
std::cout << "\tcause: " << cause << std::endl;
std::cout << "Reconnecting..." << std::endl;
nretry_ = 0;
reconnect();
}
// Callback for when a message arrives.
void message_arrived(mqtt::const_message_ptr msg) override {
std::cout << "Message arrived" << std::endl;
std::cout << "\ttopic: '" << msg->get_topic() << "'" << std::endl;
std::cout << "\tpayload: '" << msg->to_string() << "'\n" << std::endl;
}
void delivery_complete(mqtt::delivery_token_ptr token) override {}
public:
callback(mqtt::async_client& cli, mqtt::connect_options& connOpts)
: nretry_(0), cli_(cli), connOpts_(connOpts), subListener_("Subscription") {}
};
/////////////////////////////////////////////////////////////////////////////
int subscriber()
{
mqtt::connect_options connOpts;
connOpts.set_keep_alive_interval(20);
connOpts.set_clean_session(true);
mqtt::async_client client(SERVER_ADDRESS, CLIENT_ID);
callback cb(client, connOpts);
client.set_callback(cb);
// Start the connection.
// When completed, the callback will subscribe to topic.
try {
std::cout << "Connecting to the MQTT server..." << std::flush;
client.connect(connOpts, nullptr, cb);
}
catch (const mqtt::exception&) {
std::cerr << "\nERROR: Unable to connect to MQTT server: '"
<< SERVER_ADDRESS << "'" << std::endl;
return 1;
}
// Just block till user tells us to quit.
while (std::tolower(std::cin.get()) != 'q')
;
// Disconnect
try {
std::cout << "\nDisconnecting from the MQTT server..." << std::flush;
client.disconnect()->wait();
std::cout << "OK" << std::endl;
}
catch (const mqtt::exception& exc) {
std::cerr << exc.what() << std::endl;
return 1;
}
return 0;
}