mirror of
https://github.com/impact-eintr/netstack.git
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519 lines
16 KiB
Go
519 lines
16 KiB
Go
package tcp
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import (
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"fmt"
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"log"
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"math"
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"netstack/sleep"
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"netstack/tcpip"
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"netstack/tcpip/buffer"
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"netstack/tcpip/header"
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"netstack/tcpip/seqnum"
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"sync"
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"time"
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"unsafe"
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)
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const (
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// minRTO is the minimum allowed value for the retransmit timeout.
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minRTO = 200 * time.Millisecond
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// InitialCwnd is the initial congestion window.
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// 初始拥塞窗口大小
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InitialCwnd = 10
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// nDupAckThreshold is the number of duplicate ACK's required
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// before fast-retransmit is entered.
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nDupAckThreshold = 3
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)
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// NOTE 这里实现了tcp的拥塞控制 很重要
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// congestionControl is an interface that must be implemented by any supported
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// congestion control algorithm.
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// tcp拥塞控制：拥塞控制算法的接口
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type congestionControl interface {
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// HandleNDupAcks is invoked when sender.dupAckCount >= nDupAckThreshold
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// just before entering fast retransmit.
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// 在进入快速重新传输之前，当 sender.dupAckCount> = nDupAckThreshold 时调用HandleNDupAcks。
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HandleNDupAcks()
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// HandleRTOExpired is invoked when the retransmit timer expires.
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// 当重新传输计时器到期时调用HandleRTOExpired。
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HandleRTOExpired()
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// Update is invoked when processing inbound acks. It's passed the
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// number of packet's that were acked by the most recent cumulative
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// acknowledgement.
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// 已经有数据包被确认时调用 Update。它传递了最近累积确认所确认的数据包数。
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Update(packetsAcked int)
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// PostRecovery is invoked when the sender is exiting a fast retransmit/
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// recovery phase. This provides congestion control algorithms a way
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// to adjust their state when exiting recovery.
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// 当发送方退出快速重新传输/恢复阶段时，将调用PostRecovery。
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// 这为拥塞控制算法提供了一种在退出恢复时调整其状态的方法。
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PostRecovery()
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}
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/*
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+-------> sndWnd <-------+
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| |
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---------------------+-------------+----------+--------------------
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| acked | * * * * * * | # # # # #| unable send
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---------------------+-------------+----------+--------------------
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^ ^
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sndUna sndNxt
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***** in flight data
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##### able send date
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*/
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// tcp发送器，它维护了tcp必要的状态
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type sender struct {
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ep *endpoint
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// lastSendTime is the timestamp when the last packet was sent.
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// lastSendTime 是发送最后一个数据包的时间戳。
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lastSendTime time.Time
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// dupAckCount is the number of duplicated acks received. It is used for
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// fast retransmit.
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// dupAckCount 是收到的重复ack数。它用于快速重传。
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dupAckCount int
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// fr holds state related to fast recovery.
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// fr 持有与快速恢复有关的状态。
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fr fastRecovery
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// sndCwnd is the congestion window, in packets.
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// sndCwnd 是拥塞窗口，单位是包
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sndCwnd int
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// sndSsthresh is the threshold between slow start and congestion
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// avoidance.
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// sndSsthresh 是慢启动和拥塞避免之间的阈值。
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sndSsthresh int
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// sndCAAckCount is the number of packets acknowledged during congestion
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// avoidance. When enough packets have been ack'd (typically cwnd
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// packets), the congestion window is incremented by one.
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// sndCAAckCount 是拥塞避免期间确认的数据包数。当已经确认了足够的分组（通常是cwnd分组）时，拥塞窗口增加1。
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sndCAAckCount int
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// outstanding is the number of outstanding packets, that is, packets
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// that have been sent but not yet acknowledged.
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// outstanding 是正在发送的数据包的数量，即已发送但尚未确认的数据包。
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outstanding int
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// sndWnd is the send window size.
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// 发送窗口大小，单位是字节
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sndWnd seqnum.Size
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// sndUna is the next unacknowledged sequence number.
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// sndUna 是下一个未确认的序列号
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sndUna seqnum.Value
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/*
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数据流 下一个将要被缓存的数据 队列指针
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[...xxxxxxxx] => sndNxtList<-->[tail sndUna sndNxt] ---> NIC<--->NIC
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缓存队列头
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*/
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// sndNxt 是要发送的下一个段的序列号。
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sndNxt seqnum.Value
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// sndNxtList is the sequence number of the next segment to be added to
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// the send list.
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// sndNxtList 是要添加到发送列表的下一个段的序列号。
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sndNxtList seqnum.Value
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// rttMeasureSeqNum is the sequence number being used for the latest RTT
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// measurement.
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rttMeasureSeqNum seqnum.Value
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// rttMeasureTime is the time when the rttMeasureSeqNum was sent.
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rttMeasureTime time.Time
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closed bool
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writeNext *segment
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// 发送链表
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writeList segmentList
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resendTimer timer
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resendWaker sleep.Waker
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rtt rtt // 往返时间
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rto time.Duration // 超时重发时间
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srttInited bool
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// maxPayloadSize is the maximum size of the payload of a given segment.
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// It is initialized on demand.
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maxPayloadSize int
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// sndWndScale is the number of bits to shift left when reading the send
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// window size from a segment.
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sndWndScale uint8
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// maxSentAck is the maxium acknowledgement actually sent.
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maxSentAck seqnum.Value
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// cc is the congestion control algorithm in use for this sender.
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// cc 是实现拥塞控制算法的接口
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cc congestionControl
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}
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type rtt struct {
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sync.Mutex
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srtt time.Duration // 平滑 RTT 时间
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rttvar time.Duration // rtt 平均偏差 ∑|x-xbar|/n
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}
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// fastRecovery holds information related to fast recovery from a packet loss.
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//
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// +stateify savable
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// fastRecovery 保存与数据包丢失快速恢复相关的信息
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type fastRecovery struct {
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active bool
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// TODO 需要添加
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}
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// 新建并初始化发送器 irs是cookies
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func newSender(ep *endpoint, iss, irs seqnum.Value, sndWnd seqnum.Size, mss uint16, sndWndScale int) *sender {
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s := &sender{
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ep: ep,
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sndCwnd: InitialCwnd,
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sndWnd: sndWnd,
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sndUna: iss + 1,
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sndNxt: iss + 1, // 缓存长度为0
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sndNxtList: iss + 1,
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rto: 1 * time.Second,
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lastSendTime: time.Now(),
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maxPayloadSize: int(mss),
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maxSentAck: irs + 1,
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}
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// A negative sndWndScale means that no scaling is in use, otherwise we
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// store the scaling value.
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if sndWndScale > 0 {
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s.sndWndScale = uint8(sndWndScale)
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}
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s.updateMaxPayloadSize(int(ep.route.MTU()), 0)
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s.resendTimer.init(&s.resendWaker)
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return s
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}
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// updateMaxPayloadSize updates the maximum payload size based on the given
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// MTU. If this is in response to "packet too big" control packets (indicated
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// by the count argument), it also reduces the number of outstanding packets and
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// attempts to retransmit the first packet above the MTU size.
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func (s *sender) updateMaxPayloadSize(mtu, count int) {
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m := mtu - header.TCPMinimumSize
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// Calculate the maximum option size.
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// 计算MSS的大小
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var maxSackBlocks [header.TCPMaxSACKBlocks]header.SACKBlock
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options := s.ep.makeOptions(maxSackBlocks[:])
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m -= len(options)
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putOptions(options)
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// We don't adjust up for now.
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if m >= s.maxPayloadSize {
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return
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}
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// Make sure we can transmit at least one byte.
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if m <= 0 {
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m = 1
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}
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s.maxPayloadSize = m
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s.outstanding -= count
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if s.outstanding < 0 {
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s.outstanding = 0
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}
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for seg := s.writeList.Front(); seg != nil; seg = seg.Next() {
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log.Fatal("计算MSS ", m, s.maxPayloadSize, s.outstanding)
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if seg == s.writeNext {
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// We got to writeNext before we could find a segment
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// exceeding the MTU.
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break
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}
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if seg.data.Size() > m {
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// We found a segment exceeding the MTU. Rewind
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// writeNext and try to retransmit it.
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s.writeNext = seg
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break
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}
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}
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// Since we likely reduced the number of outstanding packets, we may be
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// ready to send some more.
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s.sendData()
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}
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func (s *sender) sendAck() {
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s.sendSegment(buffer.VectorisedView{}, flagAck, s.sndNxt) // seq = cookies+1 ack ack|fin.seq+1
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}
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// updateRTO 根据rtt来更新计算rto
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/*
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第一次rtt计算：
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SRTT = R
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RTTVAR = R/2
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RTO = SRTT + max (G, K*RTTVAR) = R + max(G, 2 * R)
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K = 4
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之后：
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RTTVAR = (1 - beta) * RTTVAR + beta * |SRTT - R'| = 0.75 * RTTVAR + 0.25 * |SRTT - R'|
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SRTT = (1 - alpha) * SRTT + alpha * R' = 0.875 * SRTT + 0.125 * R'
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RTO = SRTT + max (G, K*RTTVAR) = SRTT + max(G, 4 * RTTVAR)
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K = 4
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*/
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func (s *sender) updateRTO(rtt time.Duration) {
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s.rtt.Lock()
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// 第一次计算
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if !s.srttInited {
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s.rtt.srtt = rtt
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s.rtt.rttvar = rtt / 2
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s.srttInited = true
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} else {
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log.Println("之后的计算")
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// |rtt-srtt| 标准差
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diff := s.rtt.srtt - rtt
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if diff < 0 {
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diff = -diff
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}
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if !s.ep.sendTSOk {
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s.rtt.rttvar = (3*s.rtt.rttvar + diff) / 4
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s.rtt.srtt = (7*s.rtt.srtt + rtt) / 8
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} else {
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// When we are taking RTT measurements of every ACK then
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// we need to use a modified method as specified in
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// https://tools.ietf.org/html/rfc7323#appendix-G
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if s.outstanding == 0 {
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s.rtt.Unlock()
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return
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}
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// Netstack measures congestion window/inflight all in
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// terms of packets and not bytes. This is similar to
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// how linux also does cwnd and inflight. In practice
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// this approximation works as expected.
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expectedSamples := math.Ceil(float64(s.outstanding) / 2)
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// alpha & beta values are the original values as recommended in
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// https://tools.ietf.org/html/rfc6298#section-2.3.
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const alpha = 0.125
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const beta = 0.25
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alphaPrime := alpha / expectedSamples
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betaPrime := beta / expectedSamples
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rttVar := (1-betaPrime)*s.rtt.rttvar.Seconds() + betaPrime*diff.Seconds()
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srtt := (1-alphaPrime)*s.rtt.srtt.Seconds() + alphaPrime*rtt.Seconds()
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s.rtt.rttvar = time.Duration(rttVar * float64(time.Second))
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s.rtt.srtt = time.Duration(srtt * float64(time.Second))
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}
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}
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s.rto = s.rtt.srtt + 4*s.rtt.rttvar
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s.rtt.Unlock()
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if s.rto < minRTO {
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s.rto = minRTO
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}
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}
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// sendSegment sends a new segment containing the given payload, flags and
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// sequence number.
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// 根据给定的参数，负载数据、flags标记和序列号来发送数据
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func (s *sender) sendSegment(data buffer.VectorisedView, flags byte, seq seqnum.Value) *tcpip.Error {
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s.lastSendTime = time.Now()
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if seq == s.rttMeasureSeqNum {
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s.rttMeasureTime = s.lastSendTime
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}
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rcvNxt, rcvWnd := s.ep.rcv.getSendParams()
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// Remember the max sent ack.
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s.maxSentAck = rcvNxt
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log.Println(s.ep.id.LocalPort, "要求扩展窗口", rcvWnd)
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return s.ep.sendRaw(data, flags, seq, rcvNxt, rcvWnd)
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}
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// 收到段时调用 handleRcvdSegment 它负责更新与发送相关的状态
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func (s *sender) handleRcvdSegment(seg *segment) {
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// 如果rtt测量seq小于ack num，更新rto
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if !s.ep.sendTSOk && s.rttMeasureSeqNum.LessThan(seg.ackNumber) {
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s.updateRTO(time.Now().Sub(s.rttMeasureTime))
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s.rttMeasureSeqNum = s.sndNxt
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}
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// 现在某些待处理数据已被确认，或者窗口打开，或者由于快速恢复期间出现重复的ack而导致拥塞窗口膨胀，
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// 因此发送更多数据。如果需要，这也将重新启用重传计时器。
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// 存放当前窗口大小。
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s.sndWnd = seg.window
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// 获取确认号
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ack := seg.ackNumber
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// 如果ack在最小未确认的seq和segNext之间
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if (ack - 1).InRange(s.sndUna, s.sndNxt) {
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//log.Printf("[...XXXXXX]-[%d|\t%d\t|%d]==>", s.sndNxt, ack-1, s.sndUna)
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if s.ep.sendTSOk && seg.parsedOptions.TSEcr != 0 {
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// TSVal/Ecr values sent by Netstack are at a millisecond
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// granularity.
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//elapsed := time.Duration(s.ep.timestamp()-seg.parsedOptions.TSEcr) * time.Millisecond
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//s.updateRTO(elapsed)
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}
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// 获取这次确认的字节数，即 ack - snaUna
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acked := s.sndUna.Size(ack)
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// 更新下一个未确认的序列号
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s.sndUna = ack
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ackLeft := acked
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//originalOutstanding := s.outstanding
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// 从发送链表中删除已经确认的数据，发送窗口的滑动。
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//log.Printf("[...XXXXXX]-[%d|\t\t|%d]==>", s.sndNxt, s.sndUna)
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for ackLeft > 0 { // 有成功确认的数据 丢弃它们 有剩余数据的话继续发送(根据拥塞策略控制)
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seg := s.writeList.Front()
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datalen := seg.logicalLen()
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if datalen > ackLeft {
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seg.data.TrimFront(int(ackLeft))
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break
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}
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if s.writeNext == seg {
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s.writeNext = seg.Next()
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}
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// 从发送链表中删除已确认的tcp段。
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s.writeList.Remove(seg)
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// 因为有一个tcp段确认了，所以 outstanding 减1
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s.outstanding--
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seg.decRef()
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ackLeft -= datalen
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}
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// 当收到ack确认时，需要更新发送缓冲占用
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s.ep.updateSndBufferUsage(int(acked))
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// 如果发生超时重传时，s.outstanding可能会降到零以下，
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// 重置为零但后来得到一个覆盖先前发送数据的确认。
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if s.outstanding < 0 {
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s.outstanding = 0
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}
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}
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// TODO tcp拥塞控制
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if s.writeList.Front() != nil {
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log.Println(s)
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//log.Fatal(s.sndNxt, " 确认成功 继续发送 ", seg.sequenceNumber)
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}
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s.sendData()
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}
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// 发送数据段，最终调用 sendSegment 来发送
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func (s *sender) sendData() {
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limit := s.maxPayloadSize //最开始是65483
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var seg *segment
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end := s.sndUna.Add(s.sndWnd)
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var dataSent bool
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// 遍历发送链表，发送数据
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// tcp拥塞控制：s.outstanding < s.sndCwnd 判断正在发送的数据量不能超过拥塞窗口。
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for seg = s.writeNext; seg != nil && s.outstanding < s.sndCwnd; seg = seg.Next() {
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// 如果seg的flags是0，将flags改为psh|ack
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if seg.flags == 0 {
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seg.sequenceNumber = s.sndNxt
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seg.flags = flagAck | flagPsh
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}
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var segEnd seqnum.Value
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if seg.data.Size() == 0 { // 数据段没有负载，表示要结束连接
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if s.writeList.Back() != seg {
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panic("FIN segments must be the final segment in the write list.")
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}
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// 发送 fin 报文
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seg.flags = flagAck | flagFin
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// fin 报文需要确认，且消耗一个字节序列号
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segEnd = seg.sequenceNumber.Add(1)
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} else {
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// We're sending a non-FIN segment.
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if seg.flags&flagFin != 0 {
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panic("Netstack queues FIN segments without data.")
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}
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if !seg.sequenceNumber.LessThan(end) {
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log.Println("暂停数据发送 等待确认标号", seg.sequenceNumber, " 已收到 。。。。")
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break
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}
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// tcp流量控制：计算最多一次发送多大数据，
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available := int(seg.sequenceNumber.Size(end))
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if available > limit {
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available = limit
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}
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|
||
// 如果seg的payload字节数大于available
|
||
// 将seg进行分段，并且插入到该seg的后面
|
||
if seg.data.Size() > available {
|
||
nSeg := seg.clone()
|
||
nSeg.data.TrimFront(available) // NOTE 删掉用过的
|
||
nSeg.sequenceNumber.UpdateForward(seqnum.Size(available))
|
||
s.writeList.InsertAfter(seg, nSeg)
|
||
seg.data.CapLength(available)
|
||
}
|
||
|
||
s.outstanding++
|
||
segEnd = seg.sequenceNumber.Add(seqnum.Size(seg.data.Size()))
|
||
log.Println("发送窗口一开始是", s.sndWnd,
|
||
"最多发送数据", available,
|
||
"缓存数据尾", segEnd,
|
||
"发送端缓存包数量", s.outstanding)
|
||
}
|
||
|
||
if !dataSent { // 上面有个break能跳过这一步
|
||
dataSent = true
|
||
// TODO
|
||
}
|
||
|
||
s.sendSegment(seg.data, seg.flags, seg.sequenceNumber)
|
||
// 发送一个数据段后，更新sndNxt
|
||
if s.sndNxt.LessThan(segEnd) {
|
||
log.Println("更新sndNxt", s.sndNxt, " 为 ", segEnd, "下一次发送的数据头为", segEnd)
|
||
s.sndNxt = segEnd
|
||
}
|
||
}
|
||
// Remember the next segment we'll write.
|
||
s.writeNext = seg
|
||
if seg != nil {
|
||
log.Println(unsafe.Pointer(seg), seg.data.Size())
|
||
}
|
||
|
||
time.Sleep(10 * time.Millisecond)
|
||
|
||
// 如果重传定时器没有启动 且 sndUna != sndNxt 启动定时器
|
||
if !s.resendTimer.enabled() && s.sndUna != s.sndNxt {
|
||
s.resendTimer.enable(s.rto)
|
||
}
|
||
|
||
// TODO KEEPALIVE
|
||
|
||
}
|
||
|
||
var fmtSender string = `
|
||
+-----> % 10s <------+
|
||
| |
|
||
-----------------+-------------+-------------+------------------
|
||
| 已确认 |UAC% 10s|NXT% 10s| 不可发送
|
||
-----------------+-------------+-------------+------------------
|
||
^ ^
|
||
| |
|
||
% 10s % 10s`
|
||
|
||
func (s sender) String() string {
|
||
return fmt.Sprintf(fmtSender, atoi(uint32(s.sndWnd)),
|
||
atoi(uint32(s.sndNxt-s.sndUna)), atoi(s.ep.sndBufUsed),
|
||
atoi(uint32(s.sndUna)), atoi(uint32(s.sndNxt)))
|
||
}
|
||
|
||
func atoi[T int | int8 | int16 | int32 | int64 | uint | uint8 | uint16 | uint32](i T) string {
|
||
return fmt.Sprintf("%d", i)
|
||
}
|