95 lines
2.4 KiB
C++
95 lines
2.4 KiB
C++
//
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// daytime_client.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 <array>
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#include <future>
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#include <iostream>
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#include <thread>
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#include <boost/asio/io_context.hpp>
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#include <boost/asio/ip/udp.hpp>
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#include <boost/asio/use_future.hpp>
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using boost::asio::ip::udp;
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void get_daytime(boost::asio::io_context& io_context, const char* hostname)
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{
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try
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{
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udp::resolver resolver(io_context);
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std::future<udp::resolver::results_type> endpoints =
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resolver.async_resolve(
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udp::v4(), hostname, "daytime",
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boost::asio::use_future);
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// The async_resolve operation above returns the endpoints as a future
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// value that is not retrieved ...
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udp::socket socket(io_context, udp::v4());
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std::array<char, 1> send_buf = {{ 0 }};
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std::future<std::size_t> send_length =
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socket.async_send_to(boost::asio::buffer(send_buf),
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*endpoints.get().begin(), // ... until here. This call may block.
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boost::asio::use_future);
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// Do other things here while the send completes.
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send_length.get(); // Blocks until the send is complete. Throws any errors.
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std::array<char, 128> recv_buf;
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udp::endpoint sender_endpoint;
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std::future<std::size_t> recv_length =
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socket.async_receive_from(
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boost::asio::buffer(recv_buf),
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sender_endpoint,
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boost::asio::use_future);
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// Do other things here while the receive completes.
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std::cout.write(
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recv_buf.data(),
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recv_length.get()); // Blocks until receive is complete.
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}
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catch (std::system_error& e)
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{
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std::cerr << e.what() << std::endl;
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}
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}
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int main(int argc, char* argv[])
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{
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try
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{
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if (argc != 2)
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{
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std::cerr << "Usage: daytime_client <host>" << std::endl;
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return 1;
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}
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// We run the io_context off in its own thread so that it operates
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// completely asynchronously with respect to the rest of the program.
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boost::asio::io_context io_context;
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auto work = boost::asio::make_work_guard(io_context);
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std::thread thread([&io_context](){ io_context.run(); });
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get_daytime(io_context, argv[1]);
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io_context.stop();
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thread.join();
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}
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catch (std::exception& e)
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{
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std::cerr << e.what() << std::endl;
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}
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return 0;
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}
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