chore: rollback to the generic method for handling UTLS fingerprints

component/tls/reality.go

@@ -49,10 +49,6 @@ func GetRealityConn(ctx context.Context, conn net.Conn, fingerprint UClientHello
 			VerifyPeerCertificate:  verifier.VerifyPeerCertificate,
 		}
 
-		if !realityConfig.SupportX25519MLKEM768 && fingerprint == HelloChrome_Auto {
-			fingerprint = HelloChrome_120 // old reality server doesn't work with X25519MLKEM768
-		}
-
 		uConn := utls.UClient(conn, uConfig, fingerprint)
 		verifier.UConn = uConn
 		err := uConn.BuildHandshakeState()
@@ -60,6 +56,13 @@ func GetRealityConn(ctx context.Context, conn net.Conn, fingerprint UClientHello
 			return nil, err
 		}
 
+		if !realityConfig.SupportX25519MLKEM768 { // for X25519MLKEM768 does not work properly with the old reality server
+			err = BuildRemovedX25519MLKEM768HandshakeState(uConn)
+			if err != nil {
+				return nil, err
+			}
+		}
+
 		hello := uConn.HandshakeState.Hello
 		rawSessionID := hello.Raw[39 : 39+32] // the location of session ID
 		for i := range rawSessionID {         // https://github.com/golang/go/issues/5373

component/tls/utls.go

@@ -13,6 +13,7 @@ import (
 	"github.com/metacubex/tls"
 	utls "github.com/metacubex/utls"
 	"github.com/mroth/weightedrand/v2"
+	"golang.org/x/exp/slices"
 )
 
 type Conn = utls.Conn
@@ -279,6 +280,32 @@ func BuildWebsocketHandshakeState(c *UConn) error {
 	return nil
 }
 
+func BuildRemovedX25519MLKEM768HandshakeState(c *UConn) error {
+	// Build the handshake state. This will apply every variable of the TLS of the
+	// fingerprint in the UConn
+	if err := c.BuildHandshakeState(); err != nil {
+		return err
+	}
+	// Iterate over extensions and check
+	for _, extension := range c.Extensions {
+		if ce, ok := extension.(*utls.SupportedCurvesExtension); ok {
+			ce.Curves = slices.DeleteFunc(ce.Curves, func(curveID utls.CurveID) bool {
+				return curveID == utls.X25519MLKEM768
+			})
+		}
+		if ks, ok := extension.(*utls.KeyShareExtension); ok {
+			ks.KeyShares = slices.DeleteFunc(ks.KeyShares, func(share utls.KeyShare) bool {
+				return share.Group == utls.X25519MLKEM768
+			})
+		}
+	}
+	// Rebuild the client hello
+	if err := c.BuildHandshakeState(); err != nil {
+		return err
+	}
+	return nil
+}
+
 var globalFingerprint string
 
 func SetGlobalFingerprint(fingerprint string) {