tcp_sender.hh

/*
 * @Descripttion: 
 * @version: 
 * @Author: xp.Zhang
 * @Date: 2023-09-06 10:53:22
 * @LastEditors: xp.Zhang
 * @LastEditTime: 2023-10-13 10:47:39
 */
#ifndef SPONGE_LIBSPONGE_TCP_SENDER_HH
#define SPONGE_LIBSPONGE_TCP_SENDER_HH

#include "byte_stream.hh"
#include "tcp_config.hh"
#include "tcp_segment.hh"
#include "wrapping_integers.hh"

#include <functional>
#include <queue>

//! \brief The "sender" part of a TCP implementation.

//! Accepts a ByteStream, divides it up into segments and sends the
//! segments, keeps track of which segments are still in-flight,
//! maintains the Retransmission Timer, and retransmits in-flight
//! segments if the retransmission timer expires.
class TCPSender {
  private:
    //! our initial sequence number, the number for our SYN.
    WrappingInt32 _isn;

    std::queue<TCPSegment> _segments_outstanding{};
        //! outbound queue of segments that the TCPSender wants sent
    //只需要把要发送的segment放到这个segment out这个队列里面就行了
    std::queue<TCPSegment> _segments_out{};
    size_t _bytes_in_flight = 0;
    size_t _recv_ackno = 0;
    bool _syn_flag = false;
    bool _fin_flag = false;
    size_t _window_size = 0;

    //! retransmission timer for the connection
    unsigned int _initial_retransmission_timeout;
    //! outgoing stream of bytes that have not yet been sent
    ByteStream _stream;

    size_t _timer = 0;
    bool _timer_running = false;
    size_t _RTO = 0;
    size_t _consecutive_retransmission = 0;



    //! the (absolute) sequence number for the next byte to be sent
    uint64_t _next_seqno{0};

  public:
    //! Initialize a TCPSender
    TCPSender(const size_t capacity = TCPConfig::DEFAULT_CAPACITY,
              const uint16_t retx_timeout = TCPConfig::TIMEOUT_DFLT,
              const std::optional<WrappingInt32> fixed_isn = {});

    //! \name "Input" interface for the writer
    //!@{
    ByteStream &stream_in() { return _stream; }
    const ByteStream &stream_in() const { return _stream; }
    //!@}

    //! \name Methods that can cause the TCPSender to send a segment
    //!@{

    //! \brief A new acknowledgment was received
    // 接收端返回了确认信息。拿到该确认信息后，首先更新Sender自身的window_size状态。
    // 对于接收端确认的ackno来说，如果接收端是对新的数据进行确认，就更新Sender自身的ackno状态。
    // （Sender里window_size和ackno存的都是对面Receiver的状态
    bool ack_received(const WrappingInt32 ackno, const uint16_t window_size);

    //! \brief Generate an empty-payload segment (useful for creating empty ACK segments)
    void send_empty_segment();

    void send_segment(TCPSegment& seg);

    //! \brief create and send segments to fill as much of the window as possible
    //接收端会给Sender一个window_size。 根据这个window_size，
    //如果窗口没填满，并且发送端有数据需要发送，就可以使用fill_window发送segment
    //生成tcp segment 并且发送这些段到segment out 队列中
    void fill_window(bool send_syn = true);

    //! \brief Notifies the TCPSender of the passage of time
    void tick(const size_t ms_since_last_tick);
    //!@}

    //! \name Accessors
    //!@{

    //! \brief How many sequence numbers are occupied by segments sent but not yet acknowledged?
    //! \note count is in "sequence space," i.e. SYN and FIN each count for one byte
    //! (see TCPSegment::length_in_sequence_space())
    size_t bytes_in_flight() const;

    //! \brief Number of consecutive retransmissions that have occurred in a row
    //记录重新传输的数量
    unsigned int consecutive_retransmissions() const;

    //! \brief TCPSegments that the TCPSender has enqueued for transmission.
    //! \note These must be dequeued and sent by the TCPConnection,
    //! which will need to fill in the fields that are set by the TCPReceiver
    //! (ackno and window size) before sending.
    std::queue<TCPSegment> &segments_out() { return _segments_out;}
    //!@}

    //! \name What is the next sequence number? (used for testing)
    //!@{

    //! \brief absolute seqno for the next byte to be sent
    uint64_t next_seqno_absolute() const { return _next_seqno; }

    //! \brief relative seqno for the next byte to be sent
    WrappingInt32 next_seqno() const { return wrap(_next_seqno, _isn); }
    //!@}
};

#endif  // SPONGE_LIBSPONGE_TCP_SENDER_HH