CS144 lab4 计算机网络实验 笔记

CS144 lab4 计算机网络实验 笔记

介绍

本实验中,我们将组合TCP sender和TCP receiver实现一个完整的TCP connection

TCP是全双工连接,所以两方可以同时接收/发送信息,一端随时都有可能接收.发送信息

主要根据上图实现

tcp_connection.cc

#include "tcp_connection.hh"

#include 

using namespace std;

size_t TCPConnection::remaining_outbound_capacity() const { return _sender.stream_in().remaining_capacity(); }

size_t TCPConnection::bytes_in_flight() const { return _sender.bytes_in_flight(); }

size_t TCPConnection::unassembled_bytes() const { return _receiver.unassembled_bytes(); }

size_t TCPConnection::time_since_last_segment_received() const { return _time_since_last_segment_received; }

bool TCPConnection::active() const { return _active; }

void TCPConnection::segment_received(const TCPSegment &seg) {
    if (!_active)
        return;
    _time_since_last_segment_received = 0;
    // State: closed
    if (!_receiver.ackno().has_value() && _sender.next_seqno_absolute() == 0) {
        if (!seg.header().syn)
            return;
        _receiver.segment_received(seg);
        connect();
        return;
    }
    // State: syn sent
    if (_sender.next_seqno_absolute() > 0 && _sender.bytes_in_flight() == _sender.next_seqno_absolute() &&
        !_receiver.ackno().has_value()) {
        if (seg.payload().size())
            return;
        if (!seg.header().ack) {
            if (seg.header().syn) {
                // simultaneous open
                _receiver.segment_received(seg);
                _sender.send_empty_segment();
            }
            return;
        }
        if (seg.header().rst) {
            _receiver.stream_out().set_error();
            _sender.stream_in().set_error();
            _active = false;
            return;
        }
    }
    _receiver.segment_received(seg);
    _sender.ack_received(seg.header().ackno, seg.header().win);
    // Lab3 behavior: fill_window() will directly return without sending any segment.
    // See tcp_sender.cc line 42
    if (_sender.stream_in().buffer_empty() && seg.length_in_sequence_space())
        _sender.send_empty_segment();
    if (seg.header().rst) {
        _sender.send_empty_segment();
        unclean_shutdown();
        return;
    }
    send_sender_segments();
}

size_t TCPConnection::write(const string &data) {
    if (!data.size())
        return 0;
    size_t write_size = _sender.stream_in().write(data);
    _sender.fill_window();
    send_sender_segments();
    return write_size;
}

//! \param[in] ms_since_last_tick number of milliseconds since the last call to this method
void TCPConnection::tick(const size_t ms_since_last_tick) {
    if (!_active)
        return;
    _time_since_last_segment_received += ms_since_last_tick;
    _sender.tick(ms_since_last_tick);
    if (_sender.consecutive_retransmissions() > TCPConfig::MAX_RETX_ATTEMPTS)
        unclean_shutdown();
    send_sender_segments();
}

void TCPConnection::end_input_stream() {
    _sender.stream_in().end_input();
    _sender.fill_window();
    send_sender_segments();
}

void TCPConnection::connect() {
    _sender.fill_window();
    send_sender_segments();
}

TCPConnection::~TCPConnection() {
    try {
        if (active()) {
            cerr << "Warning: Unclean shutdown of TCPConnection\n";
            _sender.send_empty_segment();
            unclean_shutdown();
        }
    } catch (const exception &e) {
        std::cerr << "Exception destructing TCP FSM: " << e.what() << std::endl;
    }
}

void TCPConnection::send_sender_segments() {
    TCPSegment seg;
    while (!_sender.segments_out().empty()) {
        seg = _sender.segments_out().front();
        _sender.segments_out().pop();
        if (_receiver.ackno().has_value()) {
            seg.header().ack = true;
            seg.header().ackno = _receiver.ackno().value();
            seg.header().win = _receiver.window_size();
        }
        _segments_out.push(seg);
    }
    clean_shutdown();
}

void TCPConnection::unclean_shutdown() {
    // When this being called, _sender.stream_out() should not be empty.
    _receiver.stream_out().set_error();
    _sender.stream_in().set_error();
    _active = false;
    TCPSegment seg = _sender.segments_out().front();
    _sender.segments_out().pop();
    seg.header().ack = true;
    if (_receiver.ackno().has_value())
        seg.header().ackno = _receiver.ackno().value();
    seg.header().win = _receiver.window_size();
    seg.header().rst = true;
    _segments_out.push(seg);
}

void TCPConnection::clean_shutdown() {
    if (_receiver.stream_out().input_ended()) {
        if (!_sender.stream_in().eof())
            _linger_after_streams_finish = false;
        else if (_sender.bytes_in_flight() == 0) {
            if (!_linger_after_streams_finish || time_since_last_segment_received() >= 10 * _cfg.rt_timeout) {
                _active = false;
            }
        }
    }
}

tcp_connection.hh

#ifndef SPONGE_LIBSPONGE_TCP_FACTORED_HH
#define SPONGE_LIBSPONGE_TCP_FACTORED_HH

#include "tcp_config.hh"
#include "tcp_receiver.hh"
#include "tcp_sender.hh"
#include "tcp_state.hh"

//! \brief A complete endpoint of a TCP connection
class TCPConnection {
  private:
    size_t _time_since_last_segment_received{0};
    bool _active{true};

    void send_sender_segments();
    void clean_shutdown();
    void unclean_shutdown();

    TCPConfig _cfg;
    TCPReceiver _receiver{_cfg.recv_capacity};
    TCPSender _sender{_cfg.send_capacity, _cfg.rt_timeout, _cfg.fixed_isn};

    //! outbound queue of segments that the TCPConnection wants sent
    std::queue _segments_out{};

    //! Should the TCPConnection stay active (and keep ACKing)
    //! for 10 * _cfg.rt_timeout milliseconds after both streams have ended,
    //! in case the remote TCPConnection doesn't know we've received its whole stream?
    bool _linger_after_streams_finish{true};

  public:
    //! \name "Input" interface for the writer
    //!@{

    //! \brief Initiate a connection by sending a SYN segment
    void connect();

    //! \brief Write data to the outbound byte stream, and send it over TCP if possible
    //! \returns the number of bytes from `data` that were actually written.
    size_t write(const std::string &data);

    //! \returns the number of `bytes` that can be written right now.
    size_t remaining_outbound_capacity() const;

    //! \brief Shut down the outbound byte stream (still allows reading incoming data)
    void end_input_stream();
    //!@}

    //! \name "Output" interface for the reader
    //!@{

    //! \brief The inbound byte stream received from the peer
    ByteStream &inbound_stream() { return _receiver.stream_out(); }
    //!@}

    //! \name Accessors used for testing

    //!@{
    //! \brief number of bytes sent and not yet acknowledged, counting SYN/FIN each as one byte
    size_t bytes_in_flight() const;
    //! \brief number of bytes not yet reassembled
    size_t unassembled_bytes() const;
    //! \brief Number of milliseconds since the last segment was received
    size_t time_since_last_segment_received() const;
    //!< \brief summarize the state of the sender, receiver, and the connection
    TCPState state() const { return {_sender, _receiver, active(), _linger_after_streams_finish}; };
    //!@}

    //! \name Methods for the owner or operating system to call
    //!@{

    //! Called when a new segment has been received from the network
    void segment_received(const TCPSegment &seg);

    //! Called periodically when time elapses
    void tick(const size_t ms_since_last_tick);

    //! \brief TCPSegments that the TCPConnection has enqueued for transmission.
    //! \note The owner or operating system will dequeue these and
    //! put each one into the payload of a lower-layer datagram (usually Internet datagrams (IP),
    //! but could also be user datagrams (UDP) or any other kind).
    std::queue &segments_out() { return _segments_out; }

    //! \brief Is the connection still alive in any way?
    //! \returns `true` if either stream is still running or if the TCPConnection is lingering
    //! after both streams have finished (e.g. to ACK retransmissions from the peer)
    bool active() const;
    //!@}

    //! Construct a new connection from a configuration
    explicit TCPConnection(const TCPConfig &cfg) : _cfg{cfg} {}

    //! \name construction and destruction
    //! moving is allowed; copying is disallowed; default construction not possible

    //!@{
    ~TCPConnection();  //!< destructor sends a RST if the connection is still open
    TCPConnection() = delete;
    TCPConnection(TCPConnection &&other) = default;
    TCPConnection &operator=(TCPConnection &&other) = default;
    TCPConnection(const TCPConnection &other) = delete;
    TCPConnection &operator=(const TCPConnection &other) = delete;
    //!@}
};

#endif  // SPONGE_LIBSPONGE_TCP_FACTORED_HH

致此,完成TCP实验