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### Hello World over Websocket/TCP

This example illustrates the process of setting up the Client to connect to the Broker via Websocket/TCP and publish a "Hello World!" message.

    #include <boost/mqtt5/logger.hpp>
    #include <boost/mqtt5/mqtt_client.hpp>
    #include <boost/mqtt5/types.hpp>
    #include <boost/mqtt5/websocket.hpp> // WebSocket traits

    #include <boost/asio/detached.hpp>
    #include <boost/asio/io_context.hpp>
    #include <boost/asio/ip/tcp.hpp>
    #include <boost/beast/websocket.hpp>

    #include <iostream>
    #include <string>

    struct config {
        std::string brokers = "broker.hivemq.com/mqtt"; // Path example: localhost/mqtt
        uint16_t port = 8000; // 8083 is the default Webscoket/TCP MQTT port. However, HiveMQ's public broker uses 8000 instead.
        std::string client_id = "boost_mqtt5_tester";
    };

    int main(int argc, char** argv) {
        config cfg;

        if (argc == 4) {
            cfg.brokers = argv[1];
            cfg.port = uint16_t(std::stoi(argv[2]));
            cfg.client_id = argv[3];
        }

        boost::asio::io_context ioc;

        // Construct the Client with WebSocket/TCP as the underlying stream and enabled logging.
        // Since we are not establishing a secure connection, set the TlsContext template parameter to std::monostate.
        boost::mqtt5::mqtt_client<
            boost::beast::websocket::stream<boost::asio::ip::tcp::socket>,
            std::monostate,
            boost::mqtt5::logger
        > client(ioc, {}, boost::mqtt5::logger(boost::mqtt5::log_level::info));

        // If you want to use the Client without logging, initialise it with the following line instead.
        //boost::mqtt5::mqtt_client<boost::beast::websocket::stream<boost::asio::ip::tcp::socket>> client(ioc);

        client.brokers(cfg.brokers, cfg.port) // Broker that we want to connect to.
            .credentials(cfg.client_id) // Set the Client Identifier. (optional)
            .async_run(boost::asio::detached); // Start the Client.

        client.async_publish<boost::mqtt5::qos_e::at_most_once>(
            "boost-mqtt5/test", "Hello world!",
            boost::mqtt5::retain_e::no, boost::mqtt5::publish_props {},
            [&client](boost::mqtt5::error_code ec) {
                std::cout << ec.message() << std::endl;
                client.async_disconnect(boost::asio::detached);
            }
        );

        ioc.run();
    }