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This example demonstrates how to use Boost.Asio's cancellation features to add timeouts to your async operations, including the ones provided by Boost.MySQL. For that purpose, it employs C++20 coroutines. If you are not familiar with them, look at this example first.
This example assumes you have gone through the setup.
#include <boost/mysql/diagnostics.hpp> #include <boost/mysql/error_code.hpp> #include <boost/mysql/handshake_params.hpp> #include <boost/mysql/row_view.hpp> #include <boost/mysql/tcp_ssl.hpp> #include <boost/asio/awaitable.hpp> #include <boost/asio/cancel_after.hpp> #include <boost/asio/co_spawn.hpp> #include <boost/asio/io_context.hpp> #include <boost/asio/ip/tcp.hpp> #include <boost/asio/ssl/context.hpp> #include <chrono> #include <exception> #include <iostream> #if defined(BOOST_ASIO_HAS_CO_AWAIT) using boost::mysql::error_code; void print_employee(boost::mysql::row_view employee) { std::cout << "Employee '" << employee.at(0) << " " // first_name (string) << employee.at(1) << "' earns " // last_name (string) << employee.at(2) << " dollars yearly\n"; // salary (double) } /** * We use Boost.Asio's cancel_after completion token to cancel operations * after a certain time has elapsed. This is not something specific to Boost.MySQL, and * can be used with any other asynchronous operation that follows Asio's model. * If the operation times out, it will fail with a boost::asio::error::operation_aborted * error code. * * If any of the MySQL specific operations result in a timeout, the connection is left * in an unspecified state. You should close it and re-open it to get it working again. */ boost::asio::awaitable<void> coro_main( boost::mysql::tcp_ssl_connection& conn, boost::asio::ip::tcp::resolver& resolver, const boost::mysql::handshake_params& params, const char* hostname, const char* company_id ) { using boost::asio::cancel_after; constexpr std::chrono::seconds timeout(8); // Resolve hostname auto endpoints = co_await resolver .async_resolve(hostname, boost::mysql::default_port_string, cancel_after(timeout)); // Connect to server co_await conn.async_connect(*endpoints.begin(), params, cancel_after(timeout)); // We will be using company_id, which is untrusted user input, so we will use a prepared // statement. boost::mysql::statement stmt = co_await conn.async_prepare_statement( "SELECT first_name, last_name, salary FROM employee WHERE company_id = ?", cancel_after(timeout) ); // Execute the statement boost::mysql::results result; co_await conn.async_execute(stmt.bind(company_id), result, cancel_after(timeout)); // Print all the obtained rows for (boost::mysql::row_view employee : result.rows()) { print_employee(employee); } // Notify the MySQL server we want to quit, then close the underlying connection. co_await conn.async_close(cancel_after(timeout)); } void main_impl(int argc, char** argv) { if (argc != 4 && argc != 5) { std::cerr << "Usage: " << argv[0] << " <username> <password> <server-hostname> [company-id]\n"; exit(1); } const char* hostname = argv[3]; // The company_id whose employees we will be listing. This // is user-supplied input, and should be treated as untrusted. const char* company_id = argc == 5 ? argv[4] : "HGS"; // I/O context and connection. We use SSL because MySQL 8+ default settings require it. boost::asio::io_context ctx; boost::asio::ssl::context ssl_ctx(boost::asio::ssl::context::tls_client); boost::mysql::tcp_ssl_connection conn(ctx, ssl_ctx); // Connection parameters boost::mysql::handshake_params params( argv[1], // username argv[2], // password "boost_mysql_examples" // database to use; leave empty or omit for no database ); // Resolver for hostname resolution boost::asio::ip::tcp::resolver resolver(ctx.get_executor()); // The entry point. We pass in a function returning a boost::asio::awaitable<void>, as required. boost::asio::co_spawn( ctx.get_executor(), [&conn, &resolver, params, hostname, company_id] { return coro_main(conn, resolver, params, hostname, company_id); }, // If any exception is thrown in the coroutine body, rethrow it. [](std::exception_ptr ptr) { if (ptr) { std::rethrow_exception(ptr); } } ); // Calling run will actually start the requested operations. ctx.run(); } #else void main_impl(int, char**) { std::cout << "Sorry, your compiler does not support C++20 coroutines" << std::endl; } #endif int main(int argc, char** argv) { try { main_impl(argc, argv); } catch (const boost::mysql::error_with_diagnostics& err) { // Some errors include additional diagnostics, like server-provided error messages. // Security note: diagnostics::server_message may contain user-supplied values (e.g. the // field value that caused the error) and is encoded using to the connection's character set // (UTF-8 by default). Treat is as untrusted input. std::cerr << "Error: " << err.what() << '\n' << "Server diagnostics: " << err.get_diagnostics().server_message() << std::endl; return 1; } catch (const std::exception& err) { std::cerr << "Error: " << err.what() << std::endl; return 1; } }