sync_time_server.cpp

#include <boost/asio.hpp>
#include <iostream>

int main(int, char **)
{
    boost::asio::io_context context;

    auto ip = boost::asio::ip::address::from_string("127.0.0.1");
    auto ep = boost::asio::ip::tcp::endpoint{ip, 8080};

    boost::asio::ip::tcp::acceptor acc{context, ep};

    while (true)
    {
        boost::system::error_code ec;

        auto s = acc.accept(ec);
        if (ec)
        {
            std::cerr << ec.value() << ec.message() << std::endl;
            break;
        }

        auto t = std::chrono::system_clock::to_time_t(
            std::chrono::system_clock::now());

        std::array<char, 1024> time_buffer;

        auto err = ::ctime_s(time_buffer.data(), time_buffer.size(), &t);
        auto len = ::strnlen_s(time_buffer.data(), time_buffer.size());
        if (!err)
        {
            boost::asio::write(
                s, boost::asio::const_buffer{time_buffer.data(), len + 1}, ec);
        }

        s.shutdown(boost::asio::socket_base::shutdown_both, ec);
        s.close(ec);
    }

    acc.close();
}