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cert_compression.go
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cert_compression.go
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package tls
import (
"bytes"
"compress/zlib"
"errors"
"fmt"
"io"
"io/ioutil"
"github.com/andybalholm/brotli"
"golang.org/x/crypto/cryptobyte"
)
// https://github.com/refraction-networking/utls/blob/33a29038e742910d6ec82636748dfad5dd7f30ae/u_tls_extensions.go#L692
const (
certCompressionAlgs uint16 = 27
typeCertAlgCompression uint8 = 25
)
type CertAlgCompressionExtension struct {
Methods []CertCompressionAlgo
}
func (e *CertAlgCompressionExtension) writeToUConn(uc *UConn) error {
uc.extCompressCerts = true
return nil
}
func (e *CertAlgCompressionExtension) Len() int {
return 4 + 1 + (2 * len(e.Methods))
}
func (e *CertAlgCompressionExtension) Read(b []byte) (int, error) {
if len(b) < e.Len() {
return 0, io.ErrShortBuffer
}
// https://tools.ietf.org/html/draft-balfanz-tls-channelid-00
b[0] = byte(certCompressionAlgs >> 8)
b[1] = byte(certCompressionAlgs & 0xff)
extLen := 2 * len(e.Methods)
if extLen > 255 {
return 0, errors.New("too many certificate compression methods")
}
b[2] = byte((extLen + 1) >> 8)
b[3] = byte((extLen + 1) & 0xff)
b[4] = byte(extLen)
i := 5
for _, compMethod := range e.Methods {
b[i] = byte(compMethod >> 8)
b[i+1] = byte(compMethod)
i += 2
}
return e.Len(), io.EOF
}
type certAlgCompressionMessage struct {
method CertCompressionAlgo
uncompressedLength uint32
compressedCertificateMessage []byte
data []byte
}
func (m *certAlgCompressionMessage) marshal() []byte {
if m.data != nil {
return m.data
}
return []byte{} //TODO: implement it
}
func (m *certAlgCompressionMessage) unmarshal(data []byte) bool {
m.data = append([]byte{}, data...)
s := cryptobyte.String(data[4:])
var algID uint16
if !s.ReadUint16(&algID) {
return false
}
if !s.ReadUint24(&m.uncompressedLength) {
return false
}
if !readUint24LengthPrefixed(&s, &m.compressedCertificateMessage) {
return false
}
m.method = CertCompressionAlgo(algID)
return true
}
func (m *certAlgCompressionMessage) toCertificateMsg() (*CertificateMsgTLS13, error) {
var (
decompressed []byte
r io.ReadCloser
err error
)
if m.uncompressedLength > 1<<24 {
return nil, fmt.Errorf("decompressed certificate is to large")
}
compressed := bytes.NewBuffer(m.compressedCertificateMessage)
decompressed = make([]byte, m.uncompressedLength)
switch m.method {
case CertCompressionZlib:
r, err = zlib.NewReader(compressed)
if err != nil {
decompressed, err = ioutil.ReadAll(r)
}
if err != nil {
r.Close()
}
case CertCompressionBrotli:
decompressed, err = ioutil.ReadAll(brotli.NewReader(compressed))
//TODO:Implement zstd decompression
default:
return nil, fmt.Errorf("certificate compression method %v is not supported", m.method)
}
if err != nil {
return nil, err
}
length := len(decompressed)
if length != int(m.uncompressedLength) {
return nil, fmt.Errorf("length of decompressed certificate is invalid: %v", length)
}
decompressed = append([]byte{
11, //utls.typeCertificate
byte(length >> 16),
byte(length >> 8),
byte(length),
}, decompressed...)
var mm certificateMsgTLS13
if !mm.Unmarshal(decompressed) {
return nil, fmt.Errorf("unmarshal decompressed data failed")
}
return &mm, nil
}