paho.mqtt.cpp/examples/mqttpp_chat.cpp

// mqttpp_chat.cpp
//
// This is a Paho MQTT C++ client, sample application.
//
// The "chat" application is practically the "Hello World" application for
// messaging systems. This allows a user to type in message to send to a
// "group" while seeing all the messages that the other members of the group
// send.
//
// This application is an MQTT publisher/subscriber using the C++
// asynchronous client interface, employing callbacks to receive messages
// and status updates.
//
// The sample demonstrates:
//  - Connecting to an MQTT server/broker.
//  - Publishing messages.
//  - Subscribing to a topic
//  - Receiving messages (callbacks) through a lambda function
//
// USAGE:
//     mqttpp_chat <user> <group>

/*******************************************************************************
 * Copyright (c) 2019-2023 Frank Pagliughi <fpagliughi@mindspring.com>
 *
 * All rights reserved. This program and the accompanying materials
 * are made available under the terms of the Eclipse Public License v2.0
 * and Eclipse Distribution License v1.0 which accompany this distribution.
 *
 * The Eclipse Public License is available at
 *    http://www.eclipse.org/legal/epl-v20.html
 * and the Eclipse Distribution License is available at
 *   http://www.eclipse.org/org/documents/edl-v10.php.
 *
 * Contributors:
 *    Frank Pagliughi - initial implementation and documentation
 *******************************************************************************/

#include <iostream>
#include <cstdlib>
#include <string>
#include <cstring>
#include <cctype>
#include <thread>
#include <chrono>
#include "mqtt/async_client.h"
#include "mqtt/topic.h"

/////////////////////////////////////////////////////////////////////////////

int main(int argc, char* argv[])
{
	// The broker/server address
	const std::string SERVER_ADDRESS("mqtt://localhost:1883");

	// The QoS to use for publishing and subscribing
	const int QOS = 1;

	// Tell the broker we don't want our own messages sent back to us.
	const bool NO_LOCAL = true;

	if (argc != 3) {
		std::cout << "USAGE: mqttpp_chat <user> <group>" << std::endl;
		return 1;
	}

	std::string chatUser  { argv[1] },
				chatGroup { argv[2] },
				chatTopic { "chat/"+chatGroup };

	mqtt::async_client cli(SERVER_ADDRESS, "",
						   mqtt::create_options(MQTTVERSION_5));

	// LWT message is broadcast to other users if out connection is lost

	auto lwt = mqtt::message(chatTopic, "<<<"+chatUser+" was disconnected>>>", QOS, false);

	// Set up the connect options

	auto connOpts = mqtt::connect_options_builder()
		.properties({
			{mqtt::property::SESSION_EXPIRY_INTERVAL, 604800}
		})
		.clean_start(false)
		.will(std::move(lwt))
		.keep_alive_interval(std::chrono::seconds(20))
		.finalize();

	// Set a callback for connection lost.
	// This just exits the app.

	cli.set_connection_lost_handler([](const std::string&) {
		std::cout << "*** Connection Lost  ***" << std::endl;
		exit(2);
	});

	// Set the callback for incoming messages

	cli.set_message_callback([](mqtt::const_message_ptr msg) {
		std::cout << msg->get_payload_str() << std::endl;
	});

	// We publish and subscribe to one topic,
	// so a 'topic' object is helpful.

	mqtt::topic topic { cli, "chat/"+chatGroup, QOS };

	// Start the connection.

	try {
		std::cout << "Connecting to the chat server at '" << SERVER_ADDRESS
			<< "'..." << std::flush;
		auto tok = cli.connect(connOpts);
		tok->wait();

		// Subscribe to the topic using "no local" so that
		// we don't get own messages sent back to us

		std::cout << "Ok\nJoining the group..." << std::flush;
		auto subOpts = mqtt::subscribe_options(NO_LOCAL);
		topic.subscribe(subOpts)->wait();
		std::cout << "Ok" << std::endl;
	}
	catch (const mqtt::exception& exc) {
		std::cerr << "\nERROR: Unable to connect. "
			<< exc.what() << std::endl;
		return 1;
	}

	// Let eveyone know that a new user joined the conversation.

	topic.publish("<<" + chatUser + " joined the group>>");

	// Read messages from the console and publish them.
	// Quit when the use enters an empty line.

	std::string usrMsg;

	while (std::getline(std::cin, usrMsg) && !usrMsg.empty()) {
		usrMsg = chatUser + ": " + usrMsg;
		topic.publish(usrMsg);
	}

	// Let eveyone know that the user left the conversation.

	topic.publish("<<" + chatUser + " left the group>>")->wait();

	// Disconnect

	try {
		std::cout << "Disconnecting from the chat server..." << std::flush;
		cli.disconnect()->wait();
		std::cout << "OK" << std::endl;
	}
	catch (const mqtt::exception& exc) {
		std::cerr << exc.what() << std::endl;
		return 1;
	}

 	return 0;
}