text: //
  // reference_counted.cpp
  // ~~~~~~~~~~~~~~~~~~~~~
  //
  // Copyright (c) 2003-2020 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 <boost/asio.hpp>
  #include <boost/bind/bind.hpp>
  #include <boost/enable_shared_from_this.hpp>
  #include <boost/shared_ptr.hpp>
  #include <iostream>
  #include <vector>
  
  using boost::asio::ip::tcp;
  
  // A reference-counted non-modifiable buffer class.
  class shared_const_buffer
  {
  public:
    // Construct from a std::string.
    explicit shared_const_buffer(const std::string& data)
      : data_(new std::vector<char>(data.begin(), data.end())),
        buffer_(boost::asio::buffer(*data_))
    {
    }
  
    // Implement the ConstBufferSequence requirements.
    typedef boost::asio::const_buffer value_type;
    typedef const boost::asio::const_buffer* const_iterator;
    const boost::asio::const_buffer* begin() const { return &buffer_; }
    const boost::asio::const_buffer* end() const { return &buffer_ + 1; }
  
  private:
    boost::shared_ptr<std::vector<char> > data_;
    boost::asio::const_buffer buffer_;
  };
  
  class session
    : public boost::enable_shared_from_this<session>
  {
  public:
    session(boost::asio::io_context& io_context)
      : socket_(io_context)
    {
    }
  
    tcp::socket& socket()
    {
      return socket_;
    }
  
    void start()
    {
      using namespace std; // For time_t, time and ctime.
      time_t now = time(0);
      shared_const_buffer buffer(ctime(&now));
      boost::asio::async_write(socket_, buffer,
          boost::bind(&session::handle_write, shared_from_this()));
    }
  
    void handle_write()
    {
    }
  
  private:
    // The socket used to communicate with the client.
    tcp::socket socket_;
  };
  
  typedef boost::shared_ptr<session> session_ptr;
  
  class server
  {
  public:
    server(boost::asio::io_context& io_context, short port)
      : io_context_(io_context),
        acceptor_(io_context, tcp::endpoint(tcp::v4(), port))
    {
      session_ptr new_session(new session(io_context_));
      acceptor_.async_accept(new_session->socket(),
          boost::bind(&server::handle_accept, this, new_session,
            boost::asio::placeholders::error));
    }
  
    void handle_accept(session_ptr new_session,
        const boost::system::error_code& error)
    {
      if (!error)
      {
        new_session->start();
      }
  
      new_session.reset(new session(io_context_));
      acceptor_.async_accept(new_session->socket(),
          boost::bind(&server::handle_accept, this, new_session,
            boost::asio::placeholders::error));
    }
  
  private:
    boost::asio::io_context& io_context_;
    tcp::acceptor acceptor_;
  };
  
  int main(int argc, char* argv[])
  {
    try
    {
      if (argc != 2)
      {
        std::cerr << "Usage: reference_counted <port>\n";
        return 1;
      }
  
      boost::asio::io_context io_context;
  
      using namespace std; // For atoi.
      server s(io_context, atoi(argv[1]));
  
      io_context.run();
    }
    catch (std::exception& e)
    {
      std::cerr << "Exception: " << e.what() << "\n";
    }
  
    return 0;
  }
  