70 lines
1.6 KiB
Go
70 lines
1.6 KiB
Go
package quic
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import (
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"crypto/rand"
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"math"
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"github.com/lucas-clemente/quic-go/internal/protocol"
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)
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// The packetNumberGenerator 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 guarantued to never skip two consecutive packet numbers
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type packetNumberGenerator struct {
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averagePeriod protocol.PacketNumber
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next protocol.PacketNumber
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nextToSkip protocol.PacketNumber
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}
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func newPacketNumberGenerator(initial, averagePeriod protocol.PacketNumber) *packetNumberGenerator {
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return &packetNumberGenerator{
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next: initial,
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averagePeriod: averagePeriod,
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}
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}
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func (p *packetNumberGenerator) Peek() protocol.PacketNumber {
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return p.next
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}
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func (p *packetNumberGenerator) Pop() protocol.PacketNumber {
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next := p.next
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// generate a new packet number for the next packet
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p.next++
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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 *packetNumberGenerator) generateNewSkip() error {
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num, err := p.getRandomNumber()
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if err != nil {
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return err
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}
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skip := protocol.PacketNumber(num) * (p.averagePeriod - 1) / (math.MaxUint16 / 2)
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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 + skip
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return nil
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}
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// getRandomNumber() generates a cryptographically secure random number between 0 and MaxUint16 (= 65535)
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// The expectation value is 65535/2
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func (p *packetNumberGenerator) getRandomNumber() (uint16, error) {
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b := make([]byte, 2)
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_, err := rand.Read(b)
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if err != nil {
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return 0, err
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}
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num := uint16(b[0])<<8 + uint16(b[1])
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return num, nil
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}
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