[mqtt-client] introduction v1

Summary: related to T12804

Reviewers: ivica

Reviewed By: ivica

Subscribers: miljen, iljazovic

Differential Revision: https://repo.mireo.local/D26513

example/basic_examples.cpp

@@ -0,0 +1,53 @@
+//[basic_examples
+
+
+//[publisher
+#include <iostream>
+
+#include <boost/asio/io_context.hpp>
+#include <boost/asio/ip/tcp.hpp>
+
+#include <async_mqtt5.hpp>
+
+namespace asio = boost::asio;
+
+void client_publisher() {
+	// Initialise execution context.
+	asio::io_context ioc;
+
+	// Initialise the ``__Client__``, establish connection to the Broker over TCP.
+	async_mqtt5::mqtt_client<asio::ip::tcp::socket> client (ioc.get_executor(), "");
+	client.brokers("mqtt.broker", 1883) // Broker that we want to connect to. 1883 is the default TCP port.
+		.run(); // Start the client.
+
+	client.async_publish<async_mqtt5::qos_e::at_least_once>(
+		"topic", "my application message",
+		async_mqtt5::retain_e::yes, async_mqtt5::publish_props {},
+		[](async_mqtt5::error_code ec, async_mqtt5::reason_code rc, async_mqtt5::puback_props props) {
+			if (ec)
+				std::cout << "An application error occurred: " << ec.message() << std::endl;
+			if (rc)
+				std::cout << "MQTT protocol error occurred: " << rc.message() << std::endl;
+		}
+	);
+
+	// Publish some more messages...
+
+	// After we are done with publishing all the messages, disconnect the client.
+	// You can also use mqtt_client::cancel.
+	// Either way, you should make sure all the operations completed before disconnecting the client!
+	client.async_disconnect(
+		async_mqtt5::disconnect_rc_e::normal_disconnection, async_mqtt5::disconnect_props {},
+		[](async_mqtt5::error_code ec) {
+				if (ec)
+					std::cout << "An error during disconnect occurred: " << ec.message() << std::endl;
+		});
+
+	// Start the execution.
+	ioc.run();
+}
+
+//]
+
+
+//]