size encoder and decoder

proxy/vmess/encoding/auth.go

@@ -4,6 +4,8 @@ import (
 	"crypto/md5"
 	"hash/fnv"
 
+	"golang.org/x/crypto/sha3"
+
 	"v2ray.com/core/common/serial"
 )
 
@@ -14,26 +16,6 @@ func Authenticate(b []byte) uint32 {
 	return fnv1hash.Sum32()
 }
 
-type NoOpAuthenticator struct{}
-
-func (NoOpAuthenticator) NonceSize() int {
-	return 0
-}
-
-func (NoOpAuthenticator) Overhead() int {
-	return 0
-}
-
-// Seal implements AEAD.Seal().
-func (NoOpAuthenticator) Seal(dst, nonce, plaintext, additionalData []byte) []byte {
-	return append(dst[:0], plaintext...)
-}
-
-// Open implements AEAD.Open().
-func (NoOpAuthenticator) Open(dst, nonce, ciphertext, additionalData []byte) ([]byte, error) {
-	return append(dst[:0], ciphertext...), nil
-}
-
 // FnvAuthenticator is an AEAD based on Fnv hash.
 type FnvAuthenticator struct {
 }
@@ -71,3 +53,36 @@ func GenerateChacha20Poly1305Key(b []byte) []byte {
 	copy(key[16:], t[:])
 	return key
 }
+
+type ShakeSizeParser struct {
+	shake  sha3.ShakeHash
+	buffer [2]byte
+}
+
+func NewShakeSizeParser(nonce []byte) *ShakeSizeParser {
+	shake := sha3.NewShake128()
+	shake.Write(nonce)
+	return &ShakeSizeParser{
+		shake: shake,
+	}
+}
+
+func (s *ShakeSizeParser) SizeBytes() int {
+	return 2
+}
+
+func (s *ShakeSizeParser) next() uint16 {
+	s.shake.Read(s.buffer[:])
+	return serial.BytesToUint16(s.buffer[:])
+}
+
+func (s *ShakeSizeParser) Decode(b []byte) (uint16, error) {
+	mask := s.next()
+	size := serial.BytesToUint16(b)
+	return mask ^ size, nil
+}
+
+func (s *ShakeSizeParser) Encode(size uint16, b []byte) []byte {
+	mask := s.next()
+	return serial.Uint16ToBytes(mask^size, b[:0])
+}