refactor: split CompressCertExtension changes

- Split most of changes for `CompressCertExtension` made to `crypto/tls` files out and moved them to `u_` files.
- Edited some `crypto/tls` files to achieve better programmability for uTLS.
- Minor styling fix.

common.go

@@ -89,6 +89,7 @@ const (
 	extensionSupportedPoints         uint16 = 11
 	extensionSignatureAlgorithms     uint16 = 13
 	extensionALPN                    uint16 = 16
+	extensionStatusRequestV2         uint16 = 17
 	extensionSCT                     uint16 = 18
 	extensionDelegatedCredentials    uint16 = 34
 	extensionSessionTicket           uint16 = 35
@@ -100,7 +101,7 @@ const (
 	extensionCertificateAuthorities  uint16 = 47
 	extensionSignatureAlgorithmsCert uint16 = 50
 	extensionKeyShare                uint16 = 51
-	extensionNextProtoNeg            uint16 = 13172 // not IANA assigned // Pending discussion on whether or not remove this. crypto/tls removed it on Nov 21, 2019.  
+	extensionNextProtoNeg            uint16 = 13172 // not IANA assigned // Pending discussion on whether or not remove this. crypto/tls removed it on Nov 21, 2019.
 	extensionRenegotiationInfo       uint16 = 0xff01
 )
 

conn.go

@@ -1081,11 +1081,14 @@ func (c *Conn) readHandshake() (any, error) {
 		m = new(endOfEarlyDataMsg)
 	case typeKeyUpdate:
 		m = new(keyUpdateMsg)
-	// [UTLS SECTION BEGINS]
-	case typeCompressedCertificate:
-		m = new(compressedCertificateMsg)
-	// [UTLS SECTION ENDS]
 	default:
+		// [UTLS SECTION BEGINS]
+		var err error
+		m, err = c.utlsHandshakeMessageType(data[0]) // see u_conn.go
+		if err == nil {
+			break
+		}
+		// [UTLS SECTION ENDS]
 		return nil, c.in.setErrorLocked(c.sendAlert(alertUnexpectedMessage))
 	}
 

handshake_client_tls13.go

@@ -6,7 +6,6 @@ package tls
 
 import (
 	"bytes"
-	"compress/zlib"
 	"context"
 	"crypto"
 	"crypto/hmac"
@@ -14,12 +13,8 @@ import (
 	"errors"
 	"fmt"
 	"hash"
-	"io"
 	"sync/atomic"
 	"time"
-
-	"github.com/andybalholm/brotli"
-	"github.com/klauspost/compress/zstd"
 )
 
 type clientHandshakeStateTLS13 struct {
@@ -516,19 +511,15 @@ func (hs *clientHandshakeStateTLS13) readServerCertificate() error {
 	}
 
 	// [UTLS SECTION BEGINS]
-	receivedCompressedCert := false
+	var skipWritingCertToTranscript bool = false
-	// Check to see if we advertised any compression algorithms
+	if hs.uconn != nil {
-	if hs.uconn != nil && len(hs.uconn.certCompressionAlgs) > 0 {
+		processedMsg, err := hs.utlsReadServerCertificate(msg)
-		// Check to see if the message is a compressed certificate message, otherwise move on.
+		if err != nil {
-		compressedCertMsg, ok := msg.(*compressedCertificateMsg)
+			return err
-		if ok {
+		}
-			receivedCompressedCert = true
+		if processedMsg != nil {
-			hs.transcript.Write(compressedCertMsg.marshal())
+			skipWritingCertToTranscript = true
-
+			msg = processedMsg // msg is now a processed-by-extension certificateMsg
-			msg, err = hs.decompressCert(*compressedCertMsg)
-			if err != nil {
-				return fmt.Errorf("tls: failed to decompress certificate message: %w", err)
-			}
 		}
 	}
 	// [UTLS SECTION ENDS]
@@ -544,7 +535,7 @@ func (hs *clientHandshakeStateTLS13) readServerCertificate() error {
 	}
 	// [UTLS SECTION BEGINS]
 	// Previously, this was simply 'hs.transcript.Write(certMsg.marshal())' (without the if).
-	if !receivedCompressedCert {
+	if !skipWritingCertToTranscript {
 		hs.transcript.Write(certMsg.marshal())
 	}
 	// [UTLS SECTION ENDS]
@@ -729,80 +720,6 @@ func (hs *clientHandshakeStateTLS13) sendClientFinished() error {
 	return nil
 }
 
-// [UTLS SECTION BEGINS]
-func (hs *clientHandshakeStateTLS13) decompressCert(m compressedCertificateMsg) (*certificateMsgTLS13, error) {
-	var (
-		decompressed io.Reader
-		compressed   = bytes.NewReader(m.compressedCertificateMessage)
-		c            = hs.c
-	)
-
-	// Check to see if the peer responded with an algorithm we advertised.
-	supportedAlg := false
-	for _, alg := range hs.uconn.certCompressionAlgs {
-		if m.algorithm == uint16(alg) {
-			supportedAlg = true
-		}
-	}
-	if !supportedAlg {
-		c.sendAlert(alertBadCertificate)
-		return nil, fmt.Errorf("unadvertised algorithm (%d)", m.algorithm)
-	}
-
-	switch CertCompressionAlgo(m.algorithm) {
-	case CertCompressionBrotli:
-		decompressed = brotli.NewReader(compressed)
-
-	case CertCompressionZlib:
-		rc, err := zlib.NewReader(compressed)
-		if err != nil {
-			c.sendAlert(alertBadCertificate)
-			return nil, fmt.Errorf("failed to open zlib reader: %w", err)
-		}
-		defer rc.Close()
-		decompressed = rc
-
-	case CertCompressionZstd:
-		rc, err := zstd.NewReader(compressed)
-		if err != nil {
-			c.sendAlert(alertBadCertificate)
-			return nil, fmt.Errorf("failed to open zstd reader: %w", err)
-		}
-		defer rc.Close()
-		decompressed = rc
-
-	default:
-		c.sendAlert(alertBadCertificate)
-		return nil, fmt.Errorf("unsupported algorithm (%d)", m.algorithm)
-	}
-
-	rawMsg := make([]byte, m.uncompressedLength+4) // +4 for message type and uint24 length field
-	rawMsg[0] = typeCertificate
-	rawMsg[1] = uint8(m.uncompressedLength >> 16)
-	rawMsg[2] = uint8(m.uncompressedLength >> 8)
-	rawMsg[3] = uint8(m.uncompressedLength)
-
-	n, err := decompressed.Read(rawMsg[4:])
-	if err != nil {
-		c.sendAlert(alertBadCertificate)
-		return nil, err
-	}
-	if n < len(rawMsg)-4 {
-		// If, after decompression, the specified length does not match the actual length, the party
-		// receiving the invalid message MUST abort the connection with the "bad_certificate" alert.
-		// https://datatracker.ietf.org/doc/html/rfc8879#section-4
-		c.sendAlert(alertBadCertificate)
-		return nil, fmt.Errorf("decompressed len (%d) does not match specified len (%d)", n, m.uncompressedLength)
-	}
-	certMsg := new(certificateMsgTLS13)
-	if !certMsg.unmarshal(rawMsg) {
-		return nil, c.sendAlert(alertUnexpectedMessage)
-	}
-	return certMsg, nil
-}
-
-// [UTLS SECTION ENDS]
-
 func (c *Conn) handleNewSessionTicket(msg *newSessionTicketMsgTLS13) error {
 	if !c.isClient {
 		c.sendAlert(alertUnexpectedMessage)

u_common.go

@@ -16,6 +16,14 @@ import (
 // Things, supported by utls, but not crypto/tls' are prefixed with "utls"
 // Supported things, that have changed their ID are prefixed with "Old"
 // Supported but disabled things are prefixed with "Disabled". We will _enable_ them.
+
+// TLS handshake message types.
+const (
+	// https://datatracker.ietf.org/doc/html/rfc8879#section-7.2
+	typeCompressedCertificate uint8 = 25
+)
+
+// TLS
 const (
 	utlsExtensionPadding              uint16 = 21
 	utlsExtensionExtendedMasterSecret uint16 = 23 // https://tools.ietf.org/html/rfc7627
@@ -25,15 +33,10 @@ const (
 
 	// extensions with 'fake' prefix break connection, if server echoes them back
 	fakeExtensionTokenBinding         uint16 = 24
-	fakeExtensionChannelIDOld         uint16 = 30031 // not IANA assigned
+	fakeOldExtensionChannelID         uint16 = 30031 // not IANA assigned
 	fakeExtensionChannelID            uint16 = 30032 // not IANA assigned
 	fakeExtensionALPS                 uint16 = 17513 // not IANA assigned
 	fakeExtensionDelegatedCredentials uint16 = 34
-
-	fakeRecordSizeLimit uint16 = 0x001c
-
-	// https://datatracker.ietf.org/doc/html/rfc8879#section-7.2
-	typeCompressedCertificate uint8 = 25
 )
 
 const (
@@ -60,6 +63,11 @@ const (
 	FAKE_TLS_ECDHE_ECDSA_WITH_3DES_EDE_CBC_SHA = uint16(0xc008)
 )
 
+// Other things
+const (
+	fakeRecordSizeLimit uint16 = 0x001c
+)
+
 // newest signatures
 var (
 	FakePKCS1WithSHA224 SignatureScheme = 0x0301

u_conn.go

@@ -710,3 +710,13 @@ func makeSupportedVersions(minVers, maxVers uint16) []uint16 {
 	}
 	return a
 }
+
+// Extending (*Conn).readHandshake() to support more customized handshake messages.
+func (c *Conn) utlsHandshakeMessageType(msgType byte) (handshakeMessage, error) {
+	switch msgType {
+	case typeCompressedCertificate:
+		return new(compressedCertificateMsg), nil
+	default:
+		return nil, c.in.setErrorLocked(c.sendAlert(alertUnexpectedMessage))
+	}
+}

u_fingerprinter.go

@@ -321,7 +321,7 @@ func (f *Fingerprinter) FingerprintClientHello(data []byte) (*ClientHelloSpec, e
 		case fakeExtensionChannelID:
 			clientHelloSpec.Extensions = append(clientHelloSpec.Extensions, &FakeChannelIDExtension{})
 
-		case fakeExtensionChannelIDOld:
+		case fakeOldExtensionChannelID:
 			clientHelloSpec.Extensions = append(clientHelloSpec.Extensions, &FakeChannelIDExtension{true})
 
 		case fakeExtensionTokenBinding:

u_handshake_client.go

@@ -0,0 +1,113 @@
+// Copyright 2022 uTLS Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package tls
+
+import (
+	"bytes"
+	"compress/zlib"
+	"fmt"
+	"io"
+
+	"github.com/andybalholm/brotli"
+	"github.com/klauspost/compress/zstd"
+)
+
+// This function is called by (*clientHandshakeStateTLS13.)readServerCertificate()
+// to retrieve the certificate out of a message read by (*Conn.)readHandshake()
+func (hs *clientHandshakeStateTLS13) utlsReadServerCertificate(msg any) (processedMsg any, err error) {
+	for _, ext := range hs.uconn.Extensions {
+		switch ext.(type) {
+		case *UtlsCompressCertExtension:
+			// Included Compressed Certificate extension
+			if len(hs.uconn.certCompressionAlgs) > 0 {
+				compressedCertMsg, ok := msg.(*compressedCertificateMsg)
+				if ok {
+					hs.transcript.Write(compressedCertMsg.marshal())
+					msg, err = hs.decompressCert(*compressedCertMsg)
+					if err != nil {
+						return nil, fmt.Errorf("tls: failed to decompress certificate message: %w", err)
+					} else {
+						return msg, nil
+					}
+				}
+			}
+		default:
+			continue
+		}
+	}
+	return nil, nil
+}
+
+// called by (*clientHandshakeStateTLS13.)utlsReadServerCertificate() when UtlsCompressCertExtension is used
+func (hs *clientHandshakeStateTLS13) decompressCert(m compressedCertificateMsg) (*certificateMsgTLS13, error) {
+	var (
+		decompressed io.Reader
+		compressed   = bytes.NewReader(m.compressedCertificateMessage)
+		c            = hs.c
+	)
+
+	// Check to see if the peer responded with an algorithm we advertised.
+	supportedAlg := false
+	for _, alg := range hs.uconn.certCompressionAlgs {
+		if m.algorithm == uint16(alg) {
+			supportedAlg = true
+		}
+	}
+	if !supportedAlg {
+		c.sendAlert(alertBadCertificate)
+		return nil, fmt.Errorf("unadvertised algorithm (%d)", m.algorithm)
+	}
+
+	switch CertCompressionAlgo(m.algorithm) {
+	case CertCompressionBrotli:
+		decompressed = brotli.NewReader(compressed)
+
+	case CertCompressionZlib:
+		rc, err := zlib.NewReader(compressed)
+		if err != nil {
+			c.sendAlert(alertBadCertificate)
+			return nil, fmt.Errorf("failed to open zlib reader: %w", err)
+		}
+		defer rc.Close()
+		decompressed = rc
+
+	case CertCompressionZstd:
+		rc, err := zstd.NewReader(compressed)
+		if err != nil {
+			c.sendAlert(alertBadCertificate)
+			return nil, fmt.Errorf("failed to open zstd reader: %w", err)
+		}
+		defer rc.Close()
+		decompressed = rc
+
+	default:
+		c.sendAlert(alertBadCertificate)
+		return nil, fmt.Errorf("unsupported algorithm (%d)", m.algorithm)
+	}
+
+	rawMsg := make([]byte, m.uncompressedLength+4) // +4 for message type and uint24 length field
+	rawMsg[0] = typeCertificate
+	rawMsg[1] = uint8(m.uncompressedLength >> 16)
+	rawMsg[2] = uint8(m.uncompressedLength >> 8)
+	rawMsg[3] = uint8(m.uncompressedLength)
+
+	n, err := decompressed.Read(rawMsg[4:])
+	if err != nil {
+		c.sendAlert(alertBadCertificate)
+		return nil, err
+	}
+	if n < len(rawMsg)-4 {
+		// If, after decompression, the specified length does not match the actual length, the party
+		// receiving the invalid message MUST abort the connection with the "bad_certificate" alert.
+		// https://datatracker.ietf.org/doc/html/rfc8879#section-4
+		c.sendAlert(alertBadCertificate)
+		return nil, fmt.Errorf("decompressed len (%d) does not match specified len (%d)", n, m.uncompressedLength)
+	}
+	certMsg := new(certificateMsgTLS13)
+	if !certMsg.unmarshal(rawMsg) {
+		return nil, c.sendAlert(alertUnexpectedMessage)
+	}
+	return certMsg, nil
+}

u_handshake_messages.go

@@ -1,3 +1,7 @@
+// Copyright 2022 uTLS Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
 package tls
 
 import (

u_tls_extensions.go

@@ -863,7 +863,7 @@ func (e *FakeChannelIDExtension) Read(b []byte) (int, error) {
 	}
 	extensionID := fakeExtensionChannelID
 	if e.OldExtensionID {
-		extensionID = fakeExtensionChannelIDOld
+		extensionID = fakeOldExtensionChannelID
 	}
 	// https://tools.ietf.org/html/draft-balfanz-tls-channelid-00
 	b[0] = byte(extensionID >> 8)