echo_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, 666};

    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;
        }

        std::array<std::uint8_t, 1024> discard_buffer;

        while (!ec)
        {
            auto l = s.read_some(boost::asio::buffer(discard_buffer), ec);
            if (ec) break;

            boost::asio::write(
                s, boost::asio::const_buffer{discard_buffer.data(), l}, ec);
        }

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

    acc.close();
}