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reduce the number of skipped packet numbers for long connections

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This commit is contained in:
Marten Seemann 2020-11-26 14:47:49 +07:00
parent 416d88990b
commit 431dff2172
4 changed files with 53 additions and 45 deletions
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18
internal/ackhandler/packet_number_generator.go
View file

@ -6,6 +6,7 @@ import (
mrand "math/rand"
"github.com/lucas-clemente/quic-go/internal/protocol"
"github.com/lucas-clemente/quic-go/internal/utils"
)
type packetNumberGenerator interface {
@ -37,8 +38,9 @@ func (p *sequentialPacketNumberGenerator) Pop() protocol.PacketNumber {
// it randomly skips a packet number every averagePeriod packets (on average).
// It is guaranteed to never skip two consecutive packet numbers.
type skippingPacketNumberGenerator struct {
rand *mrand.Rand
averagePeriod protocol.PacketNumber
rand *mrand.Rand
period protocol.PacketNumber
maxPeriod protocol.PacketNumber
next protocol.PacketNumber
nextToSkip protocol.PacketNumber
@ -46,13 +48,14 @@ type skippingPacketNumberGenerator struct {
var _ packetNumberGenerator = &skippingPacketNumberGenerator{}
func newSkippingPacketNumberGenerator(initial, averagePeriod protocol.PacketNumber) packetNumberGenerator {
func newSkippingPacketNumberGenerator(initial, initialPeriod, maxPeriod protocol.PacketNumber) packetNumberGenerator {
b := make([]byte, 8)
rand.Read(b) // it's not the end of the world if we don't get perfect random here
g := &skippingPacketNumberGenerator{
rand: mrand.New(mrand.NewSource(int64(binary.LittleEndian.Uint64(b)))),
next: initial,
averagePeriod: averagePeriod,
rand: mrand.New(mrand.NewSource(int64(binary.LittleEndian.Uint64(b)))),
next: initial,
period: initialPeriod,
maxPeriod: maxPeriod,
}
g.generateNewSkip()
return g
@ -74,5 +77,6 @@ func (p *skippingPacketNumberGenerator) Pop() protocol.PacketNumber {
func (p *skippingPacketNumberGenerator) generateNewSkip() {
// make sure that there are never two consecutive packet numbers that are skipped
p.nextToSkip = p.next + 2 + protocol.PacketNumber(p.rand.Int31n(int32(2*p.averagePeriod)))
p.nextToSkip = p.next + 2 + protocol.PacketNumber(p.rand.Int63n(int64(2*p.period)))
p.period = utils.MinPacketNumber(2*p.period, p.maxPeriod)
}

70
internal/ackhandler/packet_number_generator_test.go
View file

@ -1,7 +1,10 @@
package ackhandler
import (
"fmt"
"github.com/lucas-clemente/quic-go/internal/protocol"
. "github.com/onsi/ginkgo"
. "github.com/onsi/gomega"
)
@ -20,24 +23,17 @@ var _ = Describe("Sequential Packet Number Generator", func() {
})
var _ = Describe("Skipping Packet Number Generator", func() {
var png *skippingPacketNumberGenerator
const initialPN protocol.PacketNumber = 8
BeforeEach(func() {
png = newSkippingPacketNumberGenerator(initialPN, 100).(*skippingPacketNumberGenerator)
})
const initialPeriod protocol.PacketNumber = 25
const maxPeriod protocol.PacketNumber = 300
It("can be initialized to return any first packet number", func() {
png = newSkippingPacketNumberGenerator(12345, 100).(*skippingPacketNumberGenerator)
png := newSkippingPacketNumberGenerator(12345, initialPeriod, maxPeriod)
Expect(png.Pop()).To(Equal(protocol.PacketNumber(12345)))
})
It("gets the first packet number", func() {
num := png.Pop()
Expect(num).To(Equal(initialPN))
})
It("allows peeking", func() {
png := newSkippingPacketNumberGenerator(initialPN, initialPeriod, maxPeriod).(*skippingPacketNumberGenerator)
png.nextToSkip = 1000
Expect(png.Peek()).To(Equal(initialPN))
Expect(png.Peek()).To(Equal(initialPN))
@ -47,6 +43,7 @@ var _ = Describe("Skipping Packet Number Generator", func() {
})
It("skips a packet number", func() {
png := newSkippingPacketNumberGenerator(initialPN, initialPeriod, maxPeriod)
var last protocol.PacketNumber
var skipped bool
for i := 0; i < 1000; i++ {
@ -60,35 +57,38 @@ var _ = Describe("Skipping Packet Number Generator", func() {
Expect(skipped).To(BeTrue())
})
It("skips a specific packet number", func() {
png.nextToSkip = initialPN + 1
Expect(png.Pop()).To(Equal(initialPN))
Expect(png.Peek()).To(Equal(initialPN + 2))
Expect(png.Pop()).To(Equal(initialPN + 2))
})
It("generates a new packet number to skip", func() {
const averagePeriod = 25
png.averagePeriod = averagePeriod
const rep = 500
periods := make([][]protocol.PacketNumber, rep)
expectedPeriods := []protocol.PacketNumber{25, 50, 100, 200, 300, 300, 300}
periods := make([]protocol.PacketNumber, 0, 500)
last := initialPN
var lastSkip protocol.PacketNumber
for len(periods) < cap(periods) {
next := png.Pop()
if next > last+1 {
skipped := next - 1
Expect(skipped).To(BeNumerically(">", lastSkip+1))
periods = append(periods, skipped-lastSkip-1)
lastSkip = skipped
for i := 0; i < rep; i++ {
png := newSkippingPacketNumberGenerator(initialPN, initialPeriod, maxPeriod)
last := initialPN
lastSkip := initialPN
for len(periods[i]) < len(expectedPeriods) {
next := png.Pop()
if next > last+1 {
skipped := next - 1
Expect(skipped).To(BeNumerically(">", lastSkip+1))
periods[i] = append(periods[i], skipped-lastSkip-1)
lastSkip = skipped
}
last = next
}
last = next
}
var average float64
for _, p := range periods {
average += float64(p) / float64(len(periods))
for j := 0; j < len(expectedPeriods); j++ {
var average float64
for i := 0; i < rep; i++ {
average += float64(periods[i][j]) / float64(len(periods))
}
fmt.Fprintf(GinkgoWriter, "Period %d: %.2f (expected %d)\n", j, average, expectedPeriods[j])
tolerance := protocol.PacketNumber(5)
if t := expectedPeriods[j] / 10; t > tolerance {
tolerance = t
}
Expect(average).To(BeNumerically("~", expectedPeriods[j]+1 /* we never skip two packet numbers at the same time */, tolerance))
}
Expect(average).To(BeNumerically("~", averagePeriod+1 /* we never skip two packet numbers at the same time */, 5))
})
})

2
internal/ackhandler/sent_packet_handler.go
View file

@ -37,7 +37,7 @@ type packetNumberSpace struct {
func newPacketNumberSpace(initialPN protocol.PacketNumber, skipPNs bool, rttStats *utils.RTTStats) *packetNumberSpace {
var pns packetNumberGenerator
if skipPNs {
pns = newSkippingPacketNumberGenerator(initialPN, protocol.SkipPacketAveragePeriodLength)
pns = newSkippingPacketNumberGenerator(initialPN, protocol.SkipPacketInitialPeriod, protocol.SkipPacketMaxPeriod)
} else {
pns = newSequentialPacketNumberGenerator(initialPN)
}

8
internal/protocol/params.go
View file

@ -48,8 +48,12 @@ const MaxServerUnprocessedPackets = 1024
// MaxSessionUnprocessedPackets is the max number of packets stored in each session that are not yet processed.
const MaxSessionUnprocessedPackets = 256
// SkipPacketAveragePeriodLength is the average period length in which one packet number is skipped to prevent an Optimistic ACK attack
const SkipPacketAveragePeriodLength PacketNumber = 500
// SkipPacketInitialPeriod is the initial period length used for packet number skipping to prevent an Optimistic ACK attack.
// Every time a packet number is skipped, the period is doubled, up to SkipPacketMaxPeriod.
const SkipPacketInitialPeriod PacketNumber = 256
// SkipPacketMaxPeriod is the maximum period length used for packet number skipping.
const SkipPacketMaxPeriod PacketNumber = 128 * 1024
// MaxAcceptQueueSize is the maximum number of sessions that the server queues for accepting.
// If the queue is full, new connection attempts will be rejected.