[boost] daytime - A combined TCP/UDP asynchronous server

#include <ctime>
#include <iostream>
#include <string>
#include <boost/array.hpp>
#include <boost/bind.hpp>
#include <boost/shared_ptr.hpp>
#include <boost/enable_shared_from_this.hpp>
#include <boost/asio.hpp>

using boost::asio::ip::tcp;
using boost::asio::ip::udp;

std::string make_daytime_string()
{
    using namespace std; // For time_t, time and ctime;
    time_t now = time(0);
    return ctime(&now);
}

class tcp_connection
    : public boost::enable_shared_from_this<tcp_connection>
{
public:
    typedef boost::shared_ptr<tcp_connection> pointer;

    static pointer create(boost::asio::io_service& io_service)
    {
        return pointer(new tcp_connection(io_service));
    }

    tcp::socket& socket()
    {
        return socket_;
    }

    void start()
    {
        message_ = make_daytime_string();

        boost::asio::async_write(socket_, boost::asio::buffer(message_),
            boost::bind(&tcp_connection::handle_write, shared_from_this()));
    }

private:
    tcp_connection(boost::asio::io_service& io_service)
        : socket_(io_service)
    {
    }

    void handle_write()
    {
    }

    tcp::socket socket_;
    std::string message_;
};

class tcp_server
{
public:
    tcp_server(boost::asio::io_service& io_service)
        : acceptor_(io_service, tcp::endpoint(tcp::v4(), 13))
    {
        start_accept();
    }

private:
    void start_accept()
    {
        tcp_connection::pointer new_connection =
            tcp_connection::create(acceptor_.get_io_service());

        acceptor_.async_accept(new_connection->socket(),
            boost::bind(&tcp_server::handle_accept, this, new_connection,
                boost::asio::placeholders::error));
    }

    void handle_accept(tcp_connection::pointer new_connection,
        const boost::system::error_code& error)
    {
        if (!error)
        {
            new_connection->start();
        }

        start_accept();
    }

    tcp::acceptor acceptor_;
};

class udp_server
{
public:
    udp_server(boost::asio::io_service& io_service)
        : socket_(io_service, udp::endpoint(udp::v4(), 13))
    {
        start_receive();
    }

private:
    void start_receive()
    {
        socket_.async_receive_from(
            boost::asio::buffer(recv_buffer_), remote_endpoint_,
            boost::bind(&udp_server::handle_receive, this,
                boost::asio::placeholders::error));
    }

    void handle_receive(const boost::system::error_code& error)
    {
        if (!error || error == boost::asio::error::message_size)
        {
            boost::shared_ptr<std::string> message(
                new std::string(make_daytime_string()));

            socket_.async_send_to(boost::asio::buffer(*message), remote_endpoint_,
                boost::bind(&udp_server::handle_send, this, message));

            start_receive();
        }
    }

    void handle_send(boost::shared_ptr<std::string> /*message*/)
    {
    }

    udp::socket socket_;
    udp::endpoint remote_endpoint_;
    boost::array<char, 1> recv_buffer_;
};

int main()
{
    try
    {
        boost::asio::io_service io_service;
        tcp_server server1(io_service);
        udp_server server2(io_service);
        io_service.run();
    }
    catch (std::exception& e)
    {
        std::cerr << e.what() << std::endl;
    }

    return 0;
}