mirror of
https://github.com/v2fly/v2ray-core.git
synced 2024-09-18 09:57:04 -04:00
79 lines
2.0 KiB
Go
79 lines
2.0 KiB
Go
package ackhandler
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import (
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"crypto/rand"
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"math"
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"v2ray.com/core/external/github.com/lucas-clemente/quic-go/internal/protocol"
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"v2ray.com/core/external/github.com/lucas-clemente/quic-go/internal/wire"
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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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history []protocol.PacketNumber
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}
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func newPacketNumberGenerator(initial, averagePeriod protocol.PacketNumber) *packetNumberGenerator {
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g := &packetNumberGenerator{
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next: initial,
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averagePeriod: averagePeriod,
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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 *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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if len(p.history)+1 > protocol.MaxTrackedSkippedPackets {
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p.history = p.history[1:]
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}
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p.history = append(p.history, p.next)
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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() {
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num := p.getRandomNumber()
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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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}
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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 {
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b := make([]byte, 2)
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rand.Read(b) // ignore the error here
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num := uint16(b[0])<<8 + uint16(b[1])
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return num
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}
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func (p *packetNumberGenerator) Validate(ack *wire.AckFrame) bool {
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for _, pn := range p.history {
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if ack.AcksPacket(pn) {
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return false
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}
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}
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return true
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}
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