package quic import ( "time" "github.com/lucas-clemente/quic-go/internal/ackhandler" "github.com/lucas-clemente/quic-go/internal/protocol" "github.com/lucas-clemente/quic-go/internal/utils" "github.com/lucas-clemente/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 }