mirror of
https://github.com/impact-eintr/netstack.git
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151 lines
5.0 KiB
Go
151 lines
5.0 KiB
Go
package tcp
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import (
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"netstack/logger"
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"netstack/tcpip"
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"netstack/tcpip/buffer"
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"netstack/tcpip/seqnum"
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"time"
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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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// 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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// 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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// maxSentAck is the maxium acknowledgement actually sent.
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maxSentAck seqnum.Value
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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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// 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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// 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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sndNxt: iss + 1,
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maxSentAck: irs + 1,
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}
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return s
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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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logger.TODO("发送字节序")
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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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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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// 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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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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//log.Println(unsafe.Pointer(s.ep), "怎么又调用了一次")
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var seg *segment
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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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logger.TODO("发送正常的数据, 需要流量控制")
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}
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s.sendSegment(seg.data, seg.flags, seg.sequenceNumber)
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// 发送一个数据段后，更新sndNxt
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if s.sndNxt.LessThan(segEnd) {
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s.sndNxt = segEnd
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}
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}
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// Remember the next segment we'll write.
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s.writeNext = seg
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// TODO 启动定时器
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}
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