Examples rework

Summary:
related to T15261, T15262
- all examples are added to CI checks
	- as a result, CMakeLists.txt in example folder is reworked to build all examples instead of one
	- also removed chapter Building with CMake temporarily (it will be back)
- all examples accept runtime arguments (brokers, port, clientid) (default: hivemq public broker)
- implemented example suggestions by R.Perez, most notable:
	- all examples include mqtt headers they use (no more unified headers)
	- multithreaded examples use thread_pool instead of asio::io_context
- all examples use logger with log_level::info by default

Reviewers: ivica

Reviewed By: ivica

Subscribers: iljazovic, miljen

Differential Revision: https://repo.mireo.local/D32602

example/timeout_with_awaitable_operators.cpp

@@ -5,13 +5,18 @@
 // (See accompanying file LICENSE or copy at http://www.boost.org/LICENSE_1_0.txt)
 //
 
+#include <boost/asio/use_awaitable.hpp>
+#ifdef BOOST_ASIO_HAS_CO_AWAIT
+
 //[timeout_with_awaitable_operators
 #include <chrono>
 #include <iostream>
+#include <string>
 
 #include <boost/asio/as_tuple.hpp>
 #include <boost/asio/io_context.hpp>
 #include <boost/asio/co_spawn.hpp>
+#include <boost/asio/deferred.hpp>
 #include <boost/asio/detached.hpp>
 #include <boost/asio/steady_timer.hpp>
 #include <boost/asio/use_awaitable.hpp>
@@ -19,42 +24,72 @@
 #include <boost/asio/experimental/parallel_group.hpp>
 #include <boost/asio/ip/tcp.hpp>
 
-#include <async_mqtt5.hpp>
+#include <async_mqtt5/logger.hpp>
+#include <async_mqtt5/mqtt_client.hpp>
+#include <async_mqtt5/reason_codes.hpp>
+#include <async_mqtt5/types.hpp>
 
-#ifdef BOOST_ASIO_HAS_CO_AWAIT
+struct config {
+	std::string brokers = "broker.hivemq.com";
+	uint16_t port = 1883;
+	std::string client_id = "async_mqtt5_tester";
+};
 
 // Modified completion token that will prevent co_await from throwing exceptions.
-constexpr auto use_nothrow_awaitable = boost::asio::as_tuple(boost::asio::use_awaitable);
+constexpr auto use_nothrow_awaitable = boost::asio::as_tuple(boost::asio::deferred);
 
-using client_type = async_mqtt5::mqtt_client<boost::asio::ip::tcp::socket>;
+// client_type with logging enabled
+using client_type = async_mqtt5::mqtt_client<
+	boost::asio::ip::tcp::socket, std::monostate /* TlsContext */, async_mqtt5::logger
+>;
 
-boost::asio::awaitable<void> send_over_mqtt(client_type& client, const std::string& message) {
-	client.brokers("<your-mqtt-broker>", 1883)
-		.async_run(boost::asio::detached);
+// client_type without logging
+//using client_type = async_mqtt5::mqtt_client<boost::asio::ip::tcp::socket>;
+
+boost::asio::awaitable<void> send_over_mqtt(
+	const config& cfg, client_type& client
+) {
+	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.
 
 	auto&& [pec, prc, puback_props] = co_await client.async_publish<async_mqtt5::qos_e::at_least_once>(
-		"<your-mqtt-topic>", message,
+		"async-mqtt5/test", "Hello World!",
 		async_mqtt5::retain_e::no, async_mqtt5::publish_props {},
 		use_nothrow_awaitable
 	);
 
 	co_await client.async_disconnect(use_nothrow_awaitable);
+	co_return;
 }
 
-int main() {
+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;
 
-	co_spawn(ioc, [&ioc]() -> boost::asio::awaitable<void> {
-		// Construct the Client.
-		async_mqtt5::mqtt_client<boost::asio::ip::tcp::socket> client(ioc);
+	co_spawn(
+		ioc,
+		[&ioc, &cfg]() -> boost::asio::awaitable<void> {
+		// Initialise the Client to connect to the Broker over TCP.
+		client_type client(ioc);
+
+		// You can also initialise the Client and its logger with a specific log_level (default log_level::info).
+		//client_type client(ioc, {} /* tls_context */, async_mqtt5::logger(async_mqtt5::log_level::debug));
 
 		// Construct the timer.
 		boost::asio::steady_timer timer(ioc, std::chrono::seconds(5));
 
 		using namespace boost::asio::experimental::awaitable_operators;
 		auto res = co_await (
-			send_over_mqtt(client, "Hello world!") ||
-			timer.async_wait(use_nothrow_awaitable)
+			send_over_mqtt(cfg, client) ||
+			timer.async_wait(boost::asio::as_tuple(boost::asio::use_awaitable))
 		);
 
 		// The timer expired first. The client is cancelled.
@@ -64,11 +99,24 @@ int main() {
 		else
 			std::cout << "Send over MQTT completed!" << std::endl;
 		
-	}, boost::asio::detached);
+		},
+		[](std::exception_ptr e) {
+			if (e)
+				std::rethrow_exception(e);
+		}
+	);
 
 	ioc.run();
 }
 
-#endif
-
 //]
+
+#else
+
+#include <iostream>
+
+int main() {
+	std::cout << "This example requires C++20 standard to compile and run" << std::endl;
+}
+
+#endif