forked from quic-go/quic-go
102 lines
2.5 KiB
Go
102 lines
2.5 KiB
Go
package ackhandler
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import (
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"crypto/rand"
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"encoding/binary"
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"github.com/lucas-clemente/quic-go/internal/protocol"
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"github.com/lucas-clemente/quic-go/internal/utils"
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)
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type packetNumberGenerator interface {
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Peek() protocol.PacketNumber
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Pop() protocol.PacketNumber
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}
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type sequentialPacketNumberGenerator struct {
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next protocol.PacketNumber
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}
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var _ packetNumberGenerator = &sequentialPacketNumberGenerator{}
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func newSequentialPacketNumberGenerator(initial protocol.PacketNumber) packetNumberGenerator {
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return &sequentialPacketNumberGenerator{next: initial}
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}
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func (p *sequentialPacketNumberGenerator) Peek() protocol.PacketNumber {
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return p.next
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}
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func (p *sequentialPacketNumberGenerator) Pop() protocol.PacketNumber {
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next := p.next
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p.next++
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return next
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}
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type rng struct {
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buf [4]byte
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}
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func (r *rng) Int31() int32 {
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rand.Read(r.buf[:])
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return int32(binary.BigEndian.Uint32(r.buf[:]) & ^uint32(1<<31))
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}
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// copied from the standard library math/rand implementation of Int63n
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func (r *rng) Int31n(n int32) int32 {
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if n&(n-1) == 0 { // n is power of two, can mask
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return r.Int31() & (n - 1)
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}
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max := int32((1 << 31) - 1 - (1<<31)%uint32(n))
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v := r.Int31()
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for v > max {
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v = r.Int31()
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}
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return v % n
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}
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// The skippingPacketNumberGenerator generates the packet number for the next packet
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// it randomly skips a packet number every averagePeriod packets (on average).
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// It is guaranteed to never skip two consecutive packet numbers.
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type skippingPacketNumberGenerator struct {
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period protocol.PacketNumber
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maxPeriod protocol.PacketNumber
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next protocol.PacketNumber
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nextToSkip protocol.PacketNumber
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rng rng
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}
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var _ packetNumberGenerator = &skippingPacketNumberGenerator{}
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func newSkippingPacketNumberGenerator(initial, initialPeriod, maxPeriod protocol.PacketNumber) packetNumberGenerator {
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g := &skippingPacketNumberGenerator{
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next: initial,
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period: initialPeriod,
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maxPeriod: maxPeriod,
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}
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g.generateNewSkip()
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return g
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}
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func (p *skippingPacketNumberGenerator) Peek() protocol.PacketNumber {
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return p.next
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}
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func (p *skippingPacketNumberGenerator) Pop() protocol.PacketNumber {
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next := p.next
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p.next++ // generate a new packet number for the next packet
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if p.next == p.nextToSkip {
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p.next++
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p.generateNewSkip()
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}
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return next
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}
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func (p *skippingPacketNumberGenerator) generateNewSkip() {
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// make sure that there are never two consecutive packet numbers that are skipped
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p.nextToSkip = p.next + 2 + protocol.PacketNumber(p.rng.Int31n(int32(2*p.period)))
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p.period = utils.MinPacketNumber(2*p.period, p.maxPeriod)
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}
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