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quic: basic packet operations
The type of a QUIC packet can be identified by inspecting its first byte, and the destination connection ID can be determined without decrypting and parsing the entire packet. For golang/go#58547 Change-Id: Ie298c0f6c0017343168a0974543e37ab7a569b0f Reviewed-on: https://go-review.googlesource.com/c/net/+/475437 Run-TryBot: Damien Neil <dneil@google.com> TryBot-Result: Gopher Robot <gobot@golang.org> Reviewed-by: Matt Layher <mdlayher@gmail.com> Reviewed-by: Jonathan Amsterdam <jba@google.com>
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‎internal/quic/packet.go‎

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// Copyright 2023 The Go Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style
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// license that can be found in the LICENSE file.
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package quic
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// packetType is a QUIC packet type.
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// https://www.rfc-editor.org/rfc/rfc9000.html#section-17
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type packetType byte
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const (
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packetTypeInvalid = packetType(iota)
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packetTypeInitial
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packetType0RTT
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packetTypeHandshake
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packetTypeRetry
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packetType1RTT
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packetTypeVersionNegotiation
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)
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// Bits set in the first byte of a packet.
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const (
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headerFormLong = 0x80 // https://www.rfc-editor.org/rfc/rfc9000.html#section-17.2-3.2.1
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headerFormShort = 0x00 // https://www.rfc-editor.org/rfc/rfc9000.html#section-17.3.1-4.2.1
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fixedBit = 0x40 // https://www.rfc-editor.org/rfc/rfc9000.html#section-17.2-3.4.1
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reservedBits = 0x0c // https://www.rfc-editor.org/rfc/rfc9000#section-17.2-8.2.1
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)
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// Long Packet Type bits.
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// https://www.rfc-editor.org/rfc/rfc9000.html#section-17.2-3.6.1
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const (
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longPacketTypeInitial = 0 << 4
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longPacketType0RTT = 1 << 4
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longPacketTypeHandshake = 2 << 4
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longPacketTypeRetry = 3 << 4
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)
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// Frame types.
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// https://www.rfc-editor.org/rfc/rfc9000.html#section-19
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const (
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frameTypePadding = 0x00
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frameTypePing = 0x01
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frameTypeAck = 0x02
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frameTypeAckECN = 0x03
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frameTypeResetStream = 0x04
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frameTypeStopSending = 0x05
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frameTypeCrypto = 0x06
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frameTypeNewToken = 0x07
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frameTypeStreamBase = 0x08 // low three bits carry stream flags
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frameTypeMaxData = 0x10
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frameTypeMaxStreamData = 0x11
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frameTypeMaxStreamsBidi = 0x12
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frameTypeMaxStreamsUni = 0x13
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frameTypeDataBlocked = 0x14
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frameTypeStreamDataBlocked = 0x15
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frameTypeStreamsBlockedBidi = 0x16
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frameTypeStreamsBlockedUni = 0x17
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frameTypeNewConnectionID = 0x18
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frameTypeRetireConnectionID = 0x19
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frameTypePathChallenge = 0x1a
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frameTypePathResponse = 0x1b
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frameTypeConnectionCloseTransport = 0x1c
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frameTypeConnectionCloseApplication = 0x1d
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frameTypeHandshakeDone = 0x1e
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)
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// The low three bits of STREAM frames.
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// https://www.rfc-editor.org/rfc/rfc9000.html#section-19.8
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const (
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streamOffBit = 0x04
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streamLenBit = 0x02
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streamFinBit = 0x01
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)
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// isLongHeader returns true if b is the first byte of a long header.
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func isLongHeader(b byte) bool {
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return b&headerFormLong == headerFormLong
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}
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// getPacketType returns the type of a packet.
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func getPacketType(b []byte) packetType {
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if len(b) == 0 {
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return packetTypeInvalid
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}
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if !isLongHeader(b[0]) {
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if b[0]&fixedBit != fixedBit {
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return packetTypeInvalid
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}
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return packetType1RTT
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}
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if len(b) < 5 {
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return packetTypeInvalid
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}
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if b[1] == 0 && b[2] == 0 && b[3] == 0 && b[4] == 0 {
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// Version Negotiation packets don't necessarily set the fixed bit.
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return packetTypeVersionNegotiation
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}
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if b[0]&fixedBit != fixedBit {
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return packetTypeInvalid
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}
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switch b[0] & 0x30 {
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case longPacketTypeInitial:
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return packetTypeInitial
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case longPacketType0RTT:
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return packetType0RTT
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case longPacketTypeHandshake:
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return packetTypeHandshake
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case longPacketTypeRetry:
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return packetTypeRetry
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}
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return packetTypeInvalid
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}
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// dstConnIDForDatagram returns the destination connection ID field of the
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// first QUIC packet in a datagram.
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func dstConnIDForDatagram(pkt []byte) (id []byte, ok bool) {
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if len(pkt) < 1 {
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return nil, false
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}
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var n int
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var b []byte
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if isLongHeader(pkt[0]) {
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if len(pkt) < 6 {
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return nil, false
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}
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n = int(pkt[5])
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b = pkt[6:]
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} else {
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n = connIDLen
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b = pkt[1:]
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}
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if len(b) < n {
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return nil, false
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}
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return b[:n], true
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}
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// A longPacket is a long header packet.
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type longPacket struct {
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ptype packetType
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reservedBits uint8
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version uint32
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num packetNumber
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dstConnID []byte
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srcConnID []byte
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payload []byte
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// The extra data depends on the packet type:
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// Initial: Token.
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// Retry: Retry token and integrity tag.
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extra []byte
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}
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// A shortPacket is a short header (1-RTT) packet.
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type shortPacket struct {
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reservedBits uint8
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num packetNumber
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payload []byte
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}

‎internal/quic/packet_test.go‎

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// Copyright 2023 The Go Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style
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// license that can be found in the LICENSE file.
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package quic
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import (
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"bytes"
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"encoding/hex"
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"strings"
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"testing"
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)
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func TestPacketHeader(t *testing.T) {
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for _, test := range []struct {
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name string
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packet []byte
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isLongHeader bool
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packetType packetType
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dstConnID []byte
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}{{
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// Initial packet from https://www.rfc-editor.org/rfc/rfc9001#section-a.1
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// (truncated)
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name: "rfc9001_a1",
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packet: unhex(`
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c000000001088394c8f03e5157080000 449e7b9aec34d1b1c98dd7689fb8ec11
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`),
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isLongHeader: true,
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packetType: packetTypeInitial,
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dstConnID: unhex(`8394c8f03e515708`),
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}, {
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// Initial packet from https://www.rfc-editor.org/rfc/rfc9001#section-a.3
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// (truncated)
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name: "rfc9001_a3",
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packet: unhex(`
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cf000000010008f067a5502a4262b500 4075c0d95a482cd0991cd25b0aac406a
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`),
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isLongHeader: true,
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packetType: packetTypeInitial,
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dstConnID: []byte{},
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}, {
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// Retry packet from https://www.rfc-editor.org/rfc/rfc9001#section-a.4
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name: "rfc9001_a4",
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packet: unhex(`
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ff000000010008f067a5502a4262b574 6f6b656e04a265ba2eff4d829058fb3f
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0f2496ba
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`),
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isLongHeader: true,
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packetType: packetTypeRetry,
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dstConnID: []byte{},
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}, {
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// Short header packet from https://www.rfc-editor.org/rfc/rfc9001#section-a.5
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name: "rfc9001_a5",
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packet: unhex(`
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4cfe4189655e5cd55c41f69080575d7999c25a5bfb
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`),
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isLongHeader: false,
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packetType: packetType1RTT,
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dstConnID: unhex(`fe4189655e5cd55c`),
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}, {
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// Version Negotiation packet.
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name: "version_negotiation",
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packet: unhex(`
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80 00000000 01ff0001020304
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`),
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isLongHeader: true,
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packetType: packetTypeVersionNegotiation,
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dstConnID: []byte{0xff},
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}, {
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// Too-short packet.
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name: "truncated_after_connid_length",
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packet: unhex(`
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cf0000000105
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`),
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isLongHeader: true,
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packetType: packetTypeInitial,
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dstConnID: nil,
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}, {
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// Too-short packet.
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name: "truncated_after_version",
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packet: unhex(`
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cf00000001
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`),
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isLongHeader: true,
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packetType: packetTypeInitial,
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dstConnID: nil,
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}, {
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// Much too short packet.
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name: "truncated_in_version",
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packet: unhex(`
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cf000000
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`),
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isLongHeader: true,
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packetType: packetTypeInvalid,
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dstConnID: nil,
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}} {
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t.Run(test.name, func(t *testing.T) {
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if got, want := isLongHeader(test.packet[0]), test.isLongHeader; got != want {
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t.Errorf("packet %x:\nisLongHeader(packet) = %v, want %v", test.packet, got, want)
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}
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if got, want := getPacketType(test.packet), test.packetType; got != want {
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t.Errorf("packet %x:\ngetPacketType(packet) = %v, want %v", test.packet, got, want)
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}
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gotConnID, gotOK := dstConnIDForDatagram(test.packet)
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wantConnID, wantOK := test.dstConnID, test.dstConnID != nil
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if !bytes.Equal(gotConnID, wantConnID) || gotOK != wantOK {
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t.Errorf("packet %x:\ndstConnIDForDatagram(packet) = {%x}, %v; want {%x}, %v", test.packet, gotConnID, gotOK, wantConnID, wantOK)
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}
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})
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}
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}
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func unhex(s string) []byte {
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b, err := hex.DecodeString(strings.Map(func(c rune) rune {
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switch c {
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case ' ', '\t', '\n':
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return -1
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}
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return c
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}, s))
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if err != nil {
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panic(err)
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}
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return b
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}

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