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//
// composed_1.cpp
// ~~~~~~~~~~~~~~
//
// Copyright (c) 2003-2023 Christopher M. Kohlhoff (chris at kohlhoff dot com)
//
// Distributed under the Boost Software License, Version 1.0. (See accompanying
// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
//
#include <boost/asio/deferred.hpp>
#include <boost/asio/io_context.hpp>
#include <boost/asio/ip/tcp.hpp>
#include <boost/asio/use_future.hpp>
#include <boost/asio/write.hpp>
#include <cstring>
#include <iostream>
#include <string>
#include <type_traits>
#include <utility>
using boost::asio::ip::tcp;
//------------------------------------------------------------------------------
// This is the simplest example of a composed asynchronous operation, where we
// simply repackage an existing operation. The asynchronous operation
// requirements are met by delegating responsibility to the underlying
// operation.
template <
boost::asio::completion_token_for<void(boost::system::error_code, std::size_t)>
CompletionToken>
auto async_write_message(tcp::socket& socket,
const char* message, CompletionToken&& token)
// The return type of the initiating function is deduced from the combination
// of:
//
// - the CompletionToken type,
// - the completion handler signature, and
// - the asynchronous operation's initiation function object.
//
// When the completion token is a simple callback, the return type is void.
// However, when the completion token is boost::asio::yield_context (used for
// stackful coroutines) the return type would be std::size_t, and when the
// completion token is boost::asio::use_future it would be std::future<std::size_t>.
// When the completion token is boost::asio::deferred, the return type differs for
// each asynchronous operation.
//
// In C++20 we can omit the return type as it is automatically deduced from
// the return type of our underlying asynchronous operation.
{
// When delegating to the underlying operation we must take care to perfectly
// forward the completion token. This ensures that our operation works
// correctly with move-only function objects as callbacks, as well as other
// completion token types.
return boost::asio::async_write(socket,
boost::asio::buffer(message, std::strlen(message)),
std::forward<CompletionToken>(token));
}
//------------------------------------------------------------------------------
void test_callback()
{
boost::asio::io_context io_context;
tcp::acceptor acceptor(io_context, {tcp::v4(), 55555});
tcp::socket socket = acceptor.accept();
// Test our asynchronous operation using a lambda as a callback.
async_write_message(socket, "Testing callback\r\n",
[](const boost::system::error_code& error, std::size_t n)
{
if (!error)
{
std::cout << n << " bytes transferred\n";
}
else
{
std::cout << "Error: " << error.message() << "\n";
}
});
io_context.run();
}
//------------------------------------------------------------------------------
void test_deferred()
{
boost::asio::io_context io_context;
tcp::acceptor acceptor(io_context, {tcp::v4(), 55555});
tcp::socket socket = acceptor.accept();
// Test our asynchronous operation using the deferred completion token. This
// token causes the operation's initiating function to package up the
// operation with its arguments to return a function object, which may then be
// used to launch the asynchronous operation.
boost::asio::async_operation auto op = async_write_message(
socket, "Testing deferred\r\n", boost::asio::deferred);
// Launch the operation using a lambda as a callback.
std::move(op)(
[](const boost::system::error_code& error, std::size_t n)
{
if (!error)
{
std::cout << n << " bytes transferred\n";
}
else
{
std::cout << "Error: " << error.message() << "\n";
}
});
io_context.run();
}
//------------------------------------------------------------------------------
void test_future()
{
boost::asio::io_context io_context;
tcp::acceptor acceptor(io_context, {tcp::v4(), 55555});
tcp::socket socket = acceptor.accept();
// Test our asynchronous operation using the use_future completion token.
// This token causes the operation's initiating function to return a future,
// which may be used to synchronously wait for the result of the operation.
std::future<std::size_t> f = async_write_message(
socket, "Testing future\r\n", boost::asio::use_future);
io_context.run();
try
{
// Get the result of the operation.
std::size_t n = f.get();
std::cout << n << " bytes transferred\n";
}
catch (const std::exception& e)
{
std::cout << "Error: " << e.what() << "\n";
}
}
//------------------------------------------------------------------------------
int main()
{
test_callback();
test_deferred();
test_future();
}
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