publisher & receiver examples, better completion token examples

Reviewers: iljazovic, ivica

Reviewed By: ivica

Subscribers: miljen

Differential Revision: https://repo.mireo.local/D26582

example/receiver.cpp

@@ -0,0 +1,80 @@
+//[receiver
+#include <iostream>
+
+#include <boost/asio/co_spawn.hpp>
+#include <boost/asio/detached.hpp>
+#include <boost/asio/io_context.hpp>
+#include <boost/asio/use_awaitable.hpp>
+
+#include <boost/asio/ip/tcp.hpp>
+
+#include <async_mqtt5.hpp>
+
+namespace asio = boost::asio;
+
+asio::awaitable<void> client_receiver(asio::io_context& ioc) {
+	// Initialise the ``__Client__``, establish connection to the Broker over TCP.
+	async_mqtt5::mqtt_client<asio::ip::tcp::socket> client(ioc, "");
+
+	// Configure the``__Client__``.
+	// It is mandatory to call brokers() and run() to configure the Brokers to connect to and start the Client.
+	client.brokers("mqtt.broker", 1883) // Broker that we want to connect to. 1883 is the default TCP port.
+		.run(); // Start the client.
+
+	// Configure the request to subscribe to a Topic.
+	async_mqtt5::subscribe_topic sub_topic = async_mqtt5::subscribe_topic {
+		"test/mqtt-test",
+		async_mqtt5::subscribe_options {
+			async_mqtt5::qos_e::exactly_once, // All messages will arrive at QoS 2.
+			async_mqtt5::subscribe_options::no_local_e::no, // Forward message from Clients with same ID.
+			async_mqtt5::subscribe_options::retain_as_published_e::retain, // Keep the original RETAIN flag.
+			async_mqtt5::subscribe_options::retain_handling_e::send // Send retained messages when the subscription is established.
+		}
+	};
+
+	// Subscribe to a single Topic.
+	auto [sub_codes, sub_props] = co_await client.async_subscribe(
+		sub_topic, async_mqtt5::subscribe_props {}, asio::use_awaitable
+	);
+	// Note: you can subscribe to multiple Topics in one mqtt_client::async_subscribe call.
+
+	// std::vector<async_mqtt5::reason_code> sub_codes contain the result of the subscribe action for every Topic.
+	// Before attempting to receive an Application Message from the Topic we just subscribed to,
+	// it is advisable to verify that the subscription succeeded.
+	// It is not recommended to call mqtt_client::async_receive if you do not have any
+	// Subscription established as the corresponding handler will never be invoked.
+	if (!sub_codes[0])
+		auto [topic, payload, publish_props] = co_await client.async_receive(asio::use_awaitable);
+		// Receive more messages...
+
+	// Unsubscribe from the Topic.
+	// Similar to mqtt_client::async_subscribe call, std::vector<async_mqtt5::reason_code> unsub_codes contain
+	// the result of the unsubscribe action for every Topic.
+	auto [unsub_codes, unsub_props] = co_await client.async_unsubscribe(
+		"test/mqtt-test", async_mqtt5::unsubscribe_props {},
+		asio::use_awaitable
+	);
+	// Note: you can unsubscribe from multiple Topics in one mqtt_client::async_unsubscribe call.
+
+	// Disconnect the Client.
+	co_await client.async_disconnect(
+		async_mqtt5::disconnect_rc_e::disconnect_with_will_message,
+		async_mqtt5::disconnect_props {},
+		asio::use_awaitable
+	);
+
+	co_return;
+}
+
+int main() {
+	// Initialise execution context.
+	asio::io_context ioc;
+
+	// Spawn the coroutine.
+	asio::co_spawn(ioc, client_receiver(ioc), asio::detached);
+
+	// Start the execution.
+	ioc.run();
+}
+
+//]