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 <iostream>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: closedif (!_receiver.ackno().has_value() && _sender.next_seqno_absolute() == 0) {if (!seg.header().syn)return;_receiver.segment_received(seg);connect();return;}// State: syn sentif (_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 42if (_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 sentstd::queue<TCPSegment> _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 segmentvoid 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 peerByteStream &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 bytesize_t bytes_in_flight() const;//! \brief number of bytes not yet reassembledsize_t unassembled_bytes() const;//! \brief Number of milliseconds since the last segment was receivedsize_t time_since_last_segment_received() const;//!< \brief summarize the state of the sender, receiver, and the connectionTCPState 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 networkvoid segment_received(const TCPSegment &seg);//! Called periodically when time elapsesvoid 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<TCPSegment> &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 configurationexplicit 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 openTCPConnection() = 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