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// 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 <cctype>
#include <chrono>
#include <cstdlib>
#include <cstring>
#include <iostream>
#include <string>
#include <thread>
#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);
// 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::v5()
.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 everyone 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 everyone 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;
}
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