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congestion: fix overflow when calculating the pacing budget (#3796)

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Marten Seemann 2023-05-01 14:32:20 +02:00 • committed by GitHub
parent c0b94ee4b0
commit 94829edf35
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2 changed files with 21 additions and 8 deletions
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19
internal/congestion/pacer.go
View file

@ -12,16 +12,16 @@ const maxBurstSizePackets = 10
// The pacer implements a token bucket pacing algorithm. // The pacer implements a token bucket pacing algorithm.
type pacer struct { type pacer struct {
budgetAtLastSent protocol.ByteCount budgetAtLastSent protocol.ByteCount
maxDatagramSize protocol.ByteCount maxDatagramSize protocol.ByteCount
lastSentTime time.Time lastSentTime time.Time
getAdjustedBandwidth func() uint64 // in bytes/s adjustedBandwidth func() uint64 // in bytes/s
} }
func newPacer(getBandwidth func() Bandwidth) *pacer { func newPacer(getBandwidth func() Bandwidth) *pacer {
p := &pacer{ p := &pacer{
maxDatagramSize: initialMaxDatagramSize, maxDatagramSize: initialMaxDatagramSize,
getAdjustedBandwidth: func() uint64 { adjustedBandwidth: func() uint64 {
// Bandwidth is in bits/s. We need the value in bytes/s. // Bandwidth is in bits/s. We need the value in bytes/s.
bw := uint64(getBandwidth() / BytesPerSecond) bw := uint64(getBandwidth() / BytesPerSecond)
// Use a slightly higher value than the actual measured bandwidth. // Use a slightly higher value than the actual measured bandwidth.
@ -49,13 +49,16 @@ func (p *pacer) Budget(now time.Time) protocol.ByteCount {
if p.lastSentTime.IsZero() { if p.lastSentTime.IsZero() {
return p.maxBurstSize() return p.maxBurstSize()
} }
budget := p.budgetAtLastSent + (protocol.ByteCount(p.getAdjustedBandwidth())*protocol.ByteCount(now.Sub(p.lastSentTime).Nanoseconds()))/1e9 budget := p.budgetAtLastSent + (protocol.ByteCount(p.adjustedBandwidth())*protocol.ByteCount(now.Sub(p.lastSentTime).Nanoseconds()))/1e9
if budget < 0 { // protect against overflows
budget = protocol.MaxByteCount
}
return utils.Min(p.maxBurstSize(), budget) return utils.Min(p.maxBurstSize(), budget)
} }
func (p *pacer) maxBurstSize() protocol.ByteCount { func (p *pacer) maxBurstSize() protocol.ByteCount {
return utils.Max( return utils.Max(
protocol.ByteCount(uint64((protocol.MinPacingDelay+protocol.TimerGranularity).Nanoseconds())*p.getAdjustedBandwidth())/1e9, protocol.ByteCount(uint64((protocol.MinPacingDelay+protocol.TimerGranularity).Nanoseconds())*p.adjustedBandwidth())/1e9,
maxBurstSizePackets*p.maxDatagramSize, maxBurstSizePackets*p.maxDatagramSize,
) )
} }
@ -68,7 +71,7 @@ func (p *pacer) TimeUntilSend() time.Time {
} }
return p.lastSentTime.Add(utils.Max( return p.lastSentTime.Add(utils.Max(
protocol.MinPacingDelay, protocol.MinPacingDelay,
time.Duration(math.Ceil(float64(p.maxDatagramSize-p.budgetAtLastSent)*1e9/float64(p.getAdjustedBandwidth())))*time.Nanosecond, time.Duration(math.Ceil(float64(p.maxDatagramSize-p.budgetAtLastSent)*1e9/float64(p.adjustedBandwidth())))*time.Nanosecond,
)) ))
} }

10
internal/congestion/pacer_test.go
View file

@ -1,6 +1,7 @@
package congestion package congestion
import ( import (
"math/rand"
"time" "time"
"github.com/quic-go/quic-go/internal/protocol" "github.com/quic-go/quic-go/internal/protocol"
@ -128,4 +129,13 @@ var _ = Describe("Pacer", func() {
Expect(p.TimeUntilSend()).To(Equal(t.Add(protocol.MinPacingDelay))) Expect(p.TimeUntilSend()).To(Equal(t.Add(protocol.MinPacingDelay)))
Expect(p.Budget(t.Add(protocol.MinPacingDelay))).To(Equal(protocol.ByteCount(protocol.MinPacingDelay) * initialMaxDatagramSize * 1e6 / 1e9)) Expect(p.Budget(t.Add(protocol.MinPacingDelay))).To(Equal(protocol.ByteCount(protocol.MinPacingDelay) * initialMaxDatagramSize * 1e6 / 1e9))
}) })
It("protects against overflows", func() {
p = newPacer(func() Bandwidth { return infBandwidth })
t := time.Now()
p.SentPacket(t, initialMaxDatagramSize)
for i := 0; i < 1e5; i++ {
Expect(p.Budget(t.Add(time.Duration(rand.Int63())))).To(BeNumerically(">=", 0))
}
})
}) })