text: //
  // echo_server_with_default.cpp
  // ~~~~~~~~~~~~~~~~~~~~~~~~~~~~
  //
  // Copyright (c) 2003-2019 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 <asio/co_spawn.hpp>
  #include <asio/detached.hpp>
  #include <asio/io_context.hpp>
  #include <asio/ip/tcp.hpp>
  #include <asio/signal_set.hpp>
  #include <asio/write.hpp>
  #include <cstdio>
  
  using asio::ip::tcp;
  using asio::awaitable;
  using asio::co_spawn;
  using asio::detached;
  using asio::use_awaitable_t;
  using tcp_acceptor = use_awaitable_t<>::as_default_on_t<tcp::acceptor>;
  using tcp_socket = use_awaitable_t<>::as_default_on_t<tcp::socket>;
  namespace this_coro = asio::this_coro;
  
  awaitable<void> echo(tcp_socket socket)
  {
    try
    {
      char data[1024];
      for (;;)
      {
        std::size_t n = co_await socket.async_read_some(asio::buffer(data));
        co_await async_write(socket, asio::buffer(data, n));
      }
    }
    catch (std::exception& e)
    {
      std::printf("echo Exception: %s\n", e.what());
    }
  }
  
  awaitable<void> listener()
  {
    auto executor = co_await this_coro::executor;
    tcp_acceptor acceptor(executor, {tcp::v4(), 55555});
    for (;;)
    {
      auto socket = co_await acceptor.async_accept();
      co_spawn(executor,
          [socket = std::move(socket)]() mutable
          {
            return echo(std::move(socket));
          },
          detached);
    }
  }
  
  int main()
  {
    try
    {
      asio::io_context io_context(1);
  
      asio::signal_set signals(io_context, SIGINT, SIGTERM);
      signals.async_wait([&](auto, auto){ io_context.stop(); });
  
      co_spawn(io_context, listener, detached);
  
      io_context.run();
    }
    catch (std::exception& e)
    {
      std::printf("Exception: %s\n", e.what());
    }
  }
  