cpp11chat/chat_networking.hpp

#pragma once
#include <iostream>
#include <string>
#include <vector>
#include <functional>
#include <boost/asio.hpp>
#include <algorithm>
#include "chat_messages.hpp"
#include "check_policy.hpp"



namespace chat
{
    using namespace chat;
    using namespace boost;
    using boost::asio::ip::tcp;


    /* receive_policy and send_policy must provide the static methods
     * that decide what happens with the incoming / outgoing messages.
     * you can read about the exact requirements in check_policy.hpp */
    template <class receive_policy, class send_policy>
    class client_network_manager
    {
        /* compile-time checks for whether policies are valid or not */
        static_assert(is_valid_receive_policy<receive_policy>::value,
                      "Receive policy does not supply neccessary methods!");
        static_assert(is_valid_send_policy<send_policy>::value,
                      "Send policy does not supply neccessary methods!");


    /* members */
    private:
        asio::io_service& _ios;
        tcp::socket _socket;
        asio::streambuf _isb;//<-------.    input stream
        asio::streambuf _osb;//<---.   |    output stream
        std::istream _is;//--------|---'
        std::ostream _os;//--------'

        std::string _login;
        std::vector<std::function<void(chat_message)>> _subscriptions;


    /* interface */
    public:
        client_network_manager(asio::io_service& ioservice,
                               tcp::resolver::iterator epit,
                               std::string login)
        : _ios(ioservice), _socket(_ios), _isb(), _osb(), _is(&_isb), _os(&_osb), _login(login)
        { connect(epit); }

        void send(chat_message message)
        {
            if (!send_policy::check_msg_length(message))
                return;

            _ios.post([this, message]
                      {
                          asio::async_write(_socket, asio::buffer(message.get()),
                                            [](boost::system::error_code, size_t)
                                            {});
                      });
        }

        void close_connection()
        {
            _ios.post([this]
                      {
                          _os << chat_message(message::BYE);
                          asio::write(_socket, _osb);
                          // TODO: decide what to do with last server message
                          _socket.close();
                          _ios.stop();
                      });
        }

        void subscribe(std::function<void(chat_message)> callback)
        { _subscriptions.push_back(std::move(callback)); }


    /* internal methods */
    private:
        /* throws if something went wrong on the network */
        static void throw_if_error(const boost::system::error_code& ec)
        {
            if (ec)
                throw std::runtime_error("Networking error: " + ec.message());
        }

        /* asynchronously connect to the host epit points to */
        void connect(tcp::resolver::iterator epit)
        {
            asio::async_connect
                    (
                            _socket, epit,
                            std::bind(&client_network_manager::handshake,
                                      this, std::placeholders::_1,
                                      std::placeholders::_2)
                    );
        }

        /* handles the handshake as defined in the common protocol */
        void handshake(boost::system::error_code ec, tcp::resolver::iterator)
        {
            throw_if_error(ec);

            _os << chat_message(message::HELLO);
            _os << chat_message(message::NEPTUN, _login);
            std::reverse(_login.begin(), _login.end());     // passw is neptun reversed
            _os << chat_message(message::PASSW, _login);
            asio::write(_socket, _osb);     // handshake is handled synchronously

            std::string data;
            for (int i = 0; i < 4; ++i)     // hello + 3 responses for messages above
                data += receive_message_sync() += '\n';

            receive_policy::handshake_do_what(chat_message(message::SERVER_DIRECTION, data));

            receive();                      // then flow goes to receive-loop
        }

        /* helper method used by handshake() */
        std::string receive_message_sync()
        {
            boost::system::error_code ec;

            std::string data;
            asio::read_until(_socket, _isb, byte(message::TERM), ec);
            std::getline(_is, data, byte(message::TERM));

            throw_if_error(ec);
            return data.substr(1);
        }

        /* asynchronously receive a message, and decide what to do with it */
        void receive()
        {
            asio::async_read_until
                    (_socket, _isb, byte(message::TERM),
                     [this](boost::system::error_code ec, size_t)
                     {
                         throw_if_error(ec);

                         std::string data;
                         std::getline(_is, data, byte(message::TERM));

                         char header = data[0];                         // get command byte
                         auto content = data.substr(1, data.size()-1);  // minus command & term bytes
                         chat_message msg(static_cast<message>(header), content);

                         switch (header)                                // decide what to do
                         {
                             case byte(message::PING):
                                 send(chat_message(message::PONG));
                                 break;
                             case byte(message::SERVER_DIRECTION):
                                 receive_policy::serverdirection_do_what
                                         (chat_message(message::SERVER_DIRECTION, content));
                                 break;
                             case byte(message::MESSAGE):
                                 receive_policy::message_do_what
                                         (chat_message(message::MESSAGE, content));
                                 break;
                             case byte(message::LOGIN):
                                 receive_policy::login_do_what
                                         (chat_message(message::LOGIN, content));
                                 break;
                             case byte(message::LOGOUT):
                                 receive_policy::logout_do_what
                                         (chat_message(message::LOGOUT, content));
                                 break;
                         }

                         for (auto& fun : _subscriptions)               // notify subscribers
                             fun(msg);

                         receive();                                     // receive the next message
                     });
        }
    };
}