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package ackhandler
import (
"github.com/quic-go/quic-go/internal/protocol"
"github.com/quic-go/quic-go/internal/utils"
)
type packetNumberGenerator interface {
Peek() protocol.PacketNumber
// Pop pops the packet number.
// It reports if the packet number (before the one just popped) was skipped.
// It never skips more than one packet number in a row.
Pop() (skipped bool, _ protocol.PacketNumber)
}
type sequentialPacketNumberGenerator struct {
next protocol.PacketNumber
}
var _ packetNumberGenerator = &sequentialPacketNumberGenerator{}
func newSequentialPacketNumberGenerator(initial protocol.PacketNumber) packetNumberGenerator {
return &sequentialPacketNumberGenerator{next: initial}
}
func (p *sequentialPacketNumberGenerator) Peek() protocol.PacketNumber {
return p.next
}
func (p *sequentialPacketNumberGenerator) Pop() (bool, protocol.PacketNumber) {
next := p.next
p.next++
return false, next
}
// The skippingPacketNumberGenerator generates the packet number for the next packet
// it randomly skips a packet number every averagePeriod packets (on average).
// It is guaranteed to never skip two consecutive packet numbers.
type skippingPacketNumberGenerator struct {
period protocol.PacketNumber
maxPeriod protocol.PacketNumber
next protocol.PacketNumber
nextToSkip protocol.PacketNumber
rng utils.Rand
}
var _ packetNumberGenerator = &skippingPacketNumberGenerator{}
func newSkippingPacketNumberGenerator(initial, initialPeriod, maxPeriod protocol.PacketNumber) packetNumberGenerator {
g := &skippingPacketNumberGenerator{
next: initial,
period: initialPeriod,
maxPeriod: maxPeriod,
}
g.generateNewSkip()
return g
}
func (p *skippingPacketNumberGenerator) Peek() protocol.PacketNumber {
if p.next == p.nextToSkip {
return p.next + 1
}
return p.next
}
func (p *skippingPacketNumberGenerator) Pop() (bool, protocol.PacketNumber) {
next := p.next
if p.next == p.nextToSkip {
next++
p.next += 2
p.generateNewSkip()
return true, next
}
p.next++ // generate a new packet number for the next packet
return false, next
}
func (p *skippingPacketNumberGenerator) generateNewSkip() {
// make sure that there are never two consecutive packet numbers that are skipped
p.nextToSkip = p.next + 3 + protocol.PacketNumber(p.rng.Int31n(int32(2*p.period)))
p.period = min(2*p.period, p.maxPeriod)
}
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