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mtu_discoverer.go
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mtu_discoverer.go
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package quic
import (
"time"
"github.com/kixelated/quic-go/internal/ackhandler"
"github.com/kixelated/quic-go/internal/protocol"
"github.com/kixelated/quic-go/internal/utils"
"github.com/kixelated/quic-go/internal/wire"
)
type mtuDiscoverer interface {
ShouldSendProbe(now time.Time) bool
GetPing() (ping ackhandler.Frame, datagramSize protocol.ByteCount)
}
const (
// At some point, we have to stop searching for a higher MTU.
// We're happy to send a packet that's 10 bytes smaller than the actual MTU.
maxMTUDiff = 20
// send a probe packet every mtuProbeDelay RTTs
mtuProbeDelay = 5
)
type mtuFinder struct {
lastProbeTime time.Time
probeInFlight bool
mtuIncreased func(protocol.ByteCount)
rttStats *utils.RTTStats
current protocol.ByteCount
max protocol.ByteCount // the maximum value, as advertised by the peer (or our maximum size buffer)
}
var _ mtuDiscoverer = &mtuFinder{}
func newMTUDiscoverer(rttStats *utils.RTTStats, start, max protocol.ByteCount, mtuIncreased func(protocol.ByteCount)) mtuDiscoverer {
return &mtuFinder{
current: start,
rttStats: rttStats,
lastProbeTime: time.Now(), // to make sure the first probe packet is not sent immediately
mtuIncreased: mtuIncreased,
max: max,
}
}
func (f *mtuFinder) done() bool {
return f.max-f.current <= maxMTUDiff+1
}
func (f *mtuFinder) ShouldSendProbe(now time.Time) bool {
if f.probeInFlight || f.done() {
return false
}
return !now.Before(f.lastProbeTime.Add(mtuProbeDelay * f.rttStats.SmoothedRTT()))
}
func (f *mtuFinder) GetPing() (ackhandler.Frame, protocol.ByteCount) {
size := (f.max + f.current) / 2
f.lastProbeTime = time.Now()
f.probeInFlight = true
return ackhandler.Frame{
Frame: &wire.PingFrame{},
OnLost: func(wire.Frame) {
f.probeInFlight = false
f.max = size
},
OnAcked: func(wire.Frame) {
f.probeInFlight = false
f.current = size
f.mtuIncreased(size)
},
}, size
}