text: //
  // reference_counted.cpp
  // ~~~~~~~~~~~~~~~~~~~~~
  //
  // Copyright (c) 2003-2017 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 <iostream>
  #include <memory>
  #include <utility>
  #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:
    std::shared_ptr<std::vector<char> > data_;
    boost::asio::const_buffer buffer_;
  };
  
  class session
    : public std::enable_shared_from_this<session>
  {
  public:
    session(tcp::socket socket)
      : socket_(std::move(socket))
    {
    }
  
    void start()
    {
      do_write();
    }
  
  private:
    void do_write()
    {
      std::time_t now = std::time(0);
      shared_const_buffer buffer(std::ctime(&now));
  
      auto self(shared_from_this());
      boost::asio::async_write(socket_, buffer,
          [this, self](boost::system::error_code /*ec*/, std::size_t /*length*/)
          {
          });
    }
  
    // The socket used to communicate with the client.
    tcp::socket socket_;
  };
  
  class server
  {
  public:
    server(boost::asio::io_context& io_context, short port)
      : acceptor_(io_context, tcp::endpoint(tcp::v4(), port))
    {
      do_accept();
    }
  
  private:
    void do_accept()
    {
      acceptor_.async_accept(
          [this](boost::system::error_code ec, tcp::socket socket)
          {
            if (!ec)
            {
              std::make_shared<session>(std::move(socket))->start();
            }
  
            do_accept();
          });
    }
  
    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;
  
      server s(io_context, std::atoi(argv[1]));
  
      io_context.run();
    }
    catch (std::exception& e)
    {
      std::cerr << "Exception: " << e.what() << "\n";
    }
  
    return 0;
  }
  