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// Copyright 2020 The gVisor Authors.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
package tcp
// renoRecovery stores the variables related to TCP Reno loss recovery
// algorithm.
//
// +stateify savable
type renoRecovery struct {
s *sender
}
func newRenoRecovery(s *sender) *renoRecovery {
return &renoRecovery{s: s}
}
func (rr *renoRecovery) DoRecovery(rcvdSeg *segment, fastRetransmit bool) {
ack := rcvdSeg.ackNumber
snd := rr.s
// We are in fast recovery mode. Ignore the ack if it's out of range.
if !ack.InRange(snd.SndUna, snd.SndNxt+1) {
return
}
// Don't count this as a duplicate if it is carrying data or
// updating the window.
if rcvdSeg.logicalLen() != 0 || snd.SndWnd != rcvdSeg.window {
return
}
// Inflate the congestion window if we're getting duplicate acks
// for the packet we retransmitted.
if !fastRetransmit && ack == snd.FastRecovery.First {
// We received a dup, inflate the congestion window by 1 packet
// if we're not at the max yet. Only inflate the window if
// regular FastRecovery is in use, RFC6675 does not require
// inflating cwnd on duplicate ACKs.
if snd.SndCwnd < snd.FastRecovery.MaxCwnd {
snd.SndCwnd++
}
return
}
// A partial ack was received. Retransmit this packet and remember it
// so that we don't retransmit it again.
//
// We don't inflate the window because we're putting the same packet
// back onto the wire.
//
// N.B. The retransmit timer will be reset by the caller.
snd.FastRecovery.First = ack
snd.DupAckCount = 0
snd.resendSegment()
}
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