114 lines
3.6 KiB
C++
114 lines
3.6 KiB
C++
//
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// composed_1.cpp
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// ~~~~~~~~~~~~~~
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//
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// Copyright (c) 2003-2019 Christopher M. Kohlhoff (chris at kohlhoff dot com)
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//
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// Distributed under the Boost Software License, Version 1.0. (See accompanying
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// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
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//
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#include <boost/asio/io_context.hpp>
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#include <boost/asio/ip/tcp.hpp>
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#include <boost/asio/use_future.hpp>
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#include <boost/asio/write.hpp>
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#include <cstring>
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#include <iostream>
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#include <string>
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#include <type_traits>
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#include <utility>
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using boost::asio::ip::tcp;
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//------------------------------------------------------------------------------
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// This is the simplest example of a composed asynchronous operation, where we
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// simply repackage an existing operation. The asynchronous operation
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// requirements are met by delegating responsibility to the underlying
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// operation.
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template <typename CompletionToken>
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auto async_write_message(tcp::socket& socket,
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const char* message, CompletionToken&& token)
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// The return type of the initiating function is deduced from the combination
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// of CompletionToken type and the completion handler's signature. When the
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// completion token is a simple callback, the return type is void. However,
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// when the completion token is boost::asio::yield_context (used for stackful
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// coroutines) the return type would be std::size_t, and when the completion
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// token is boost::asio::use_future it would be std::future<std::size_t>.
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//
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// In C++14 we can omit the return type as it is automatically deduced from
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// the return type of our underlying asynchronous operation
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{
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// When delegating to the underlying operation we must take care to perfectly
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// forward the completion token. This ensures that our operation works
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// correctly with move-only function objects as callbacks, as well as other
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// completion token types.
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return boost::asio::async_write(socket,
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boost::asio::buffer(message, std::strlen(message)),
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std::forward<CompletionToken>(token));
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}
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//------------------------------------------------------------------------------
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void test_callback()
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{
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boost::asio::io_context io_context;
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tcp::acceptor acceptor(io_context, {tcp::v4(), 55555});
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tcp::socket socket = acceptor.accept();
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// Test our asynchronous operation using a lambda as a callback.
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async_write_message(socket, "Testing callback\r\n",
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[](const boost::system::error_code& error, std::size_t n)
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{
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if (!error)
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{
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std::cout << n << " bytes transferred\n";
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}
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else
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{
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std::cout << "Error: " << error.message() << "\n";
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}
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});
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io_context.run();
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}
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//------------------------------------------------------------------------------
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void test_future()
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{
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boost::asio::io_context io_context;
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tcp::acceptor acceptor(io_context, {tcp::v4(), 55555});
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tcp::socket socket = acceptor.accept();
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// Test our asynchronous operation using the use_future completion token.
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// This token causes the operation's initiating function to return a future,
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// which may be used to synchronously wait for the result of the operation.
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std::future<std::size_t> f = async_write_message(
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socket, "Testing future\r\n", boost::asio::use_future);
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io_context.run();
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try
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{
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// Get the result of the operation.
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std::size_t n = f.get();
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std::cout << n << " bytes transferred\n";
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}
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catch (const std::exception& e)
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{
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std::cout << "Error: " << e.what() << "\n";
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}
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}
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//------------------------------------------------------------------------------
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int main()
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{
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test_callback();
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test_future();
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}
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