QUIC sniffer: Optimize the code (#4655)

Based on 2eed70e17d

app/dispatcher/default.go

@@ -43,7 +43,7 @@ func (r *cachedReader) Cache(b *buf.Buffer, deadline time.Duration) error {
 		r.cache, _ = buf.MergeMulti(r.cache, mb)
 	}
 	b.Clear()
-	rawBytes := b.Extend(b.Cap())
+	rawBytes := b.Extend(min(r.cache.Len(), b.Cap()))
 	n := r.cache.Copy(rawBytes)
 	b.Resize(0, int32(n))
 	r.Unlock()

common/protocol/quic/sniff.go

@@ -10,7 +10,6 @@ import (
 	"github.com/quic-go/quic-go/quicvarint"
 	"github.com/xtls/xray-core/common"
 	"github.com/xtls/xray-core/common/buf"
-	"github.com/xtls/xray-core/common/bytespool"
 	"github.com/xtls/xray-core/common/errors"
 	"github.com/xtls/xray-core/common/protocol"
 	ptls "github.com/xtls/xray-core/common/protocol/tls"
@@ -53,9 +52,9 @@ func SniffQUIC(b []byte) (*SniffHeader, error) {
 	}
 
 	// Crypto data separated across packets
-	cryptoLen := 0
-	cryptoData := bytespool.Alloc(32767)
-	defer bytespool.Free(cryptoData)
+	cryptoLen := int32(0)
+	cryptoDataBuf := buf.NewWithSize(32767)
+	defer cryptoDataBuf.Release()
 	cache := buf.New()
 	defer cache.Release()
 
@@ -143,7 +142,7 @@ func SniffQUIC(b []byte) (*SniffHeader, error) {
 
 		cache.Clear()
 		mask := cache.Extend(int32(block.BlockSize()))
-		block.Encrypt(mask, b[hdrLen+4:hdrLen+4+16])
+		block.Encrypt(mask, b[hdrLen+4:hdrLen+4+len(mask)])
 		b[0] ^= mask[0] & 0xf
 		packetNumberLength := int(b[0]&0x3 + 1)
 		for i := range packetNumberLength {
@@ -217,15 +216,15 @@ func SniffQUIC(b []byte) (*SniffHeader, error) {
 				if err != nil || length > uint64(buffer.Len()) {
 					return nil, io.ErrUnexpectedEOF
 				}
-				if cryptoLen < int(offset+length) {
-					newCryptoLen := int(offset + length)
-					if len(cryptoData) < newCryptoLen {
+				currentCryptoLen := int32(offset + length)
+				if cryptoLen < currentCryptoLen {
+					if cryptoDataBuf.Cap() < currentCryptoLen {
 						return nil, io.ErrShortBuffer
 					}
-					wipeBytes(cryptoData[cryptoLen:newCryptoLen])
-					cryptoLen = newCryptoLen
+					cryptoDataBuf.Extend(currentCryptoLen - cryptoLen)
+					cryptoLen = currentCryptoLen
 				}
-				if _, err := buffer.Read(cryptoData[offset : offset+length]); err != nil { // Field: Crypto Data
+				if _, err := buffer.Read(cryptoDataBuf.BytesRange(int32(offset), currentCryptoLen)); err != nil { // Field: Crypto Data
 					return nil, io.ErrUnexpectedEOF
 				}
 			case 0x1c: // CONNECTION_CLOSE frame, only 0x1c is permitted in initial packet
@@ -250,7 +249,7 @@ func SniffQUIC(b []byte) (*SniffHeader, error) {
 		}
 
 		tlsHdr := &ptls.SniffHeader{}
-		err = ptls.ReadClientHello(cryptoData[:cryptoLen], tlsHdr)
+		err = ptls.ReadClientHello(cryptoDataBuf.BytesRange(0, cryptoLen), tlsHdr)
 		if err != nil {
 			// The crypto data may have not been fully recovered in current packets,
 			// So we continue to sniff rest packets.
@@ -263,12 +262,6 @@ func SniffQUIC(b []byte) (*SniffHeader, error) {
 	return nil, protocol.ErrProtoNeedMoreData
 }
 
-func wipeBytes(b []byte) {
-	for i := range len(b) {
-		b[i] = 0x0
-	}
-}
-
 func hkdfExpandLabel(hash crypto.Hash, secret, context []byte, label string, length int) []byte {
 	b := make([]byte, 3, 3+6+len(label)+1+len(context))
 	binary.BigEndian.PutUint16(b, uint16(length))