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packet_unpacker.go
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packet_unpacker.go
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package quic
import (
"fmt"
"time"
"github.com/xtls/quic-go/internal/handshake"
"github.com/xtls/quic-go/internal/protocol"
"github.com/xtls/quic-go/internal/qerr"
"github.com/xtls/quic-go/internal/wire"
)
type headerDecryptor interface {
DecryptHeader(sample []byte, firstByte *byte, pnBytes []byte)
}
type headerParseError struct {
err error
}
func (e *headerParseError) Unwrap() error {
return e.err
}
func (e *headerParseError) Error() string {
return e.err.Error()
}
type unpackedPacket struct {
hdr *wire.ExtendedHeader
encryptionLevel protocol.EncryptionLevel
data []byte
}
// The packetUnpacker unpacks QUIC packets.
type packetUnpacker struct {
cs handshake.CryptoSetup
shortHdrConnIDLen int
}
var _ unpacker = &packetUnpacker{}
func newPacketUnpacker(cs handshake.CryptoSetup, shortHdrConnIDLen int) *packetUnpacker {
return &packetUnpacker{
cs: cs,
shortHdrConnIDLen: shortHdrConnIDLen,
}
}
// UnpackLongHeader unpacks a Long Header packet.
// If the reserved bits are invalid, the error is wire.ErrInvalidReservedBits.
// If any other error occurred when parsing the header, the error is of type headerParseError.
// If decrypting the payload fails for any reason, the error is the error returned by the AEAD.
func (u *packetUnpacker) UnpackLongHeader(hdr *wire.Header, data []byte) (*unpackedPacket, error) {
var encLevel protocol.EncryptionLevel
var extHdr *wire.ExtendedHeader
var decrypted []byte
//nolint:exhaustive // Retry packets can't be unpacked.
switch hdr.Type {
case protocol.PacketTypeInitial:
encLevel = protocol.EncryptionInitial
opener, err := u.cs.GetInitialOpener()
if err != nil {
return nil, err
}
extHdr, decrypted, err = u.unpackLongHeaderPacket(opener, hdr, data)
if err != nil {
return nil, err
}
case protocol.PacketTypeHandshake:
encLevel = protocol.EncryptionHandshake
opener, err := u.cs.GetHandshakeOpener()
if err != nil {
return nil, err
}
extHdr, decrypted, err = u.unpackLongHeaderPacket(opener, hdr, data)
if err != nil {
return nil, err
}
case protocol.PacketType0RTT:
encLevel = protocol.Encryption0RTT
opener, err := u.cs.Get0RTTOpener()
if err != nil {
return nil, err
}
extHdr, decrypted, err = u.unpackLongHeaderPacket(opener, hdr, data)
if err != nil {
return nil, err
}
default:
return nil, fmt.Errorf("unknown packet type: %s", hdr.Type)
}
if len(decrypted) == 0 {
return nil, &qerr.TransportError{
ErrorCode: qerr.ProtocolViolation,
ErrorMessage: "empty packet",
}
}
return &unpackedPacket{
hdr: extHdr,
encryptionLevel: encLevel,
data: decrypted,
}, nil
}
func (u *packetUnpacker) UnpackShortHeader(rcvTime time.Time, data []byte) (protocol.PacketNumber, protocol.PacketNumberLen, protocol.KeyPhaseBit, []byte, error) {
opener, err := u.cs.Get1RTTOpener()
if err != nil {
return 0, 0, 0, nil, err
}
pn, pnLen, kp, decrypted, err := u.unpackShortHeaderPacket(opener, rcvTime, data)
if err != nil {
return 0, 0, 0, nil, err
}
if len(decrypted) == 0 {
return 0, 0, 0, nil, &qerr.TransportError{
ErrorCode: qerr.ProtocolViolation,
ErrorMessage: "empty packet",
}
}
return pn, pnLen, kp, decrypted, nil
}
func (u *packetUnpacker) unpackLongHeaderPacket(opener handshake.LongHeaderOpener, hdr *wire.Header, data []byte) (*wire.ExtendedHeader, []byte, error) {
extHdr, parseErr := u.unpackLongHeader(opener, hdr, data)
// If the reserved bits are set incorrectly, we still need to continue unpacking.
// This avoids a timing side-channel, which otherwise might allow an attacker
// to gain information about the header encryption.
if parseErr != nil && parseErr != wire.ErrInvalidReservedBits {
return nil, nil, parseErr
}
extHdrLen := extHdr.ParsedLen()
extHdr.PacketNumber = opener.DecodePacketNumber(extHdr.PacketNumber, extHdr.PacketNumberLen)
decrypted, err := opener.Open(data[extHdrLen:extHdrLen], data[extHdrLen:], extHdr.PacketNumber, data[:extHdrLen])
if err != nil {
return nil, nil, err
}
if parseErr != nil {
return nil, nil, parseErr
}
return extHdr, decrypted, nil
}
func (u *packetUnpacker) unpackShortHeaderPacket(opener handshake.ShortHeaderOpener, rcvTime time.Time, data []byte) (protocol.PacketNumber, protocol.PacketNumberLen, protocol.KeyPhaseBit, []byte, error) {
l, pn, pnLen, kp, parseErr := u.unpackShortHeader(opener, data)
// If the reserved bits are set incorrectly, we still need to continue unpacking.
// This avoids a timing side-channel, which otherwise might allow an attacker
// to gain information about the header encryption.
if parseErr != nil && parseErr != wire.ErrInvalidReservedBits {
return 0, 0, 0, nil, &headerParseError{parseErr}
}
pn = opener.DecodePacketNumber(pn, pnLen)
decrypted, err := opener.Open(data[l:l], data[l:], rcvTime, pn, kp, data[:l])
if err != nil {
return 0, 0, 0, nil, err
}
return pn, pnLen, kp, decrypted, parseErr
}
func (u *packetUnpacker) unpackShortHeader(hd headerDecryptor, data []byte) (int, protocol.PacketNumber, protocol.PacketNumberLen, protocol.KeyPhaseBit, error) {
hdrLen := 1 /* first header byte */ + u.shortHdrConnIDLen
if len(data) < hdrLen+4+16 {
return 0, 0, 0, 0, fmt.Errorf("packet too small, expected at least 20 bytes after the header, got %d", len(data)-hdrLen)
}
origPNBytes := make([]byte, 4)
copy(origPNBytes, data[hdrLen:hdrLen+4])
// 2. decrypt the header, assuming a 4 byte packet number
hd.DecryptHeader(
data[hdrLen+4:hdrLen+4+16],
&data[0],
data[hdrLen:hdrLen+4],
)
// 3. parse the header (and learn the actual length of the packet number)
l, pn, pnLen, kp, parseErr := wire.ParseShortHeader(data, u.shortHdrConnIDLen)
if parseErr != nil && parseErr != wire.ErrInvalidReservedBits {
return l, pn, pnLen, kp, parseErr
}
// 4. if the packet number is shorter than 4 bytes, replace the remaining bytes with the copy we saved earlier
if pnLen != protocol.PacketNumberLen4 {
copy(data[hdrLen+int(pnLen):hdrLen+4], origPNBytes[int(pnLen):])
}
return l, pn, pnLen, kp, parseErr
}
// The error is either nil, a wire.ErrInvalidReservedBits or of type headerParseError.
func (u *packetUnpacker) unpackLongHeader(hd headerDecryptor, hdr *wire.Header, data []byte) (*wire.ExtendedHeader, error) {
extHdr, err := unpackLongHeader(hd, hdr, data)
if err != nil && err != wire.ErrInvalidReservedBits {
return nil, &headerParseError{err: err}
}
return extHdr, err
}
func unpackLongHeader(hd headerDecryptor, hdr *wire.Header, data []byte) (*wire.ExtendedHeader, error) {
hdrLen := hdr.ParsedLen()
if protocol.ByteCount(len(data)) < hdrLen+4+16 {
//nolint:stylecheck
return nil, fmt.Errorf("Packet too small. Expected at least 20 bytes after the header, got %d", protocol.ByteCount(len(data))-hdrLen)
}
// The packet number can be up to 4 bytes long, but we won't know the length until we decrypt it.
// 1. save a copy of the 4 bytes
origPNBytes := make([]byte, 4)
copy(origPNBytes, data[hdrLen:hdrLen+4])
// 2. decrypt the header, assuming a 4 byte packet number
hd.DecryptHeader(
data[hdrLen+4:hdrLen+4+16],
&data[0],
data[hdrLen:hdrLen+4],
)
// 3. parse the header (and learn the actual length of the packet number)
extHdr, parseErr := hdr.ParseExtended(data)
if parseErr != nil && parseErr != wire.ErrInvalidReservedBits {
return nil, parseErr
}
// 4. if the packet number is shorter than 4 bytes, replace the remaining bytes with the copy we saved earlier
if extHdr.PacketNumberLen != protocol.PacketNumberLen4 {
copy(data[extHdr.ParsedLen():hdrLen+4], origPNBytes[int(extHdr.PacketNumberLen):])
}
return extHdr, parseErr
}