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