feat: bridge mixed wire protocol SUDP payloads (#5347)

SUDP payload codec follows transport wireProtocol; same-protocol v1/v1 and v2/v2 keep raw join; only mixed proxy/visitor protocols use message-aware bridge; no new capability/selection field.

server/visitor/visitor.go

@@ -65,6 +65,7 @@ func (vm *Manager) Listen(name string, sk string, allowUsers []string) (*netpkg.
 
 func (vm *Manager) NewConn(name string, conn net.Conn, timestamp int64, signKey string,
 	useEncryption bool, useCompression bool, visitorUser string,
+	wireProtocol string,
 ) (err error) {
 	vm.mu.RLock()
 	defer vm.mu.RUnlock()
@@ -90,7 +91,11 @@ func (vm *Manager) NewConn(name string, conn net.Conn, timestamp int64, signKey
 		if useCompression {
 			rwc = libio.WithCompression(rwc)
 		}
-		err = l.l.PutConn(netpkg.WrapReadWriteCloserToConn(rwc, conn))
+		visitorConn := netpkg.WrapReadWriteCloserToConn(rwc, conn)
+		err = l.l.PutConn(&wireProtocolConn{
+			Conn:         visitorConn,
+			wireProtocol: wireProtocol,
+		})
 	} else {
 		err = fmt.Errorf("custom listener for [%s] doesn't exist", name)
 		return
@@ -98,6 +103,15 @@ func (vm *Manager) NewConn(name string, conn net.Conn, timestamp int64, signKey
 	return
 }
 
+type wireProtocolConn struct {
+	net.Conn
+	wireProtocol string
+}
+
+func (c *wireProtocolConn) WireProtocol() string {
+	return c.wireProtocol
+}
+
 func (vm *Manager) CloseListener(name string) {
 	vm.mu.Lock()
 	defer vm.mu.Unlock()

server/visitor/visitor_test.go

@@ -0,0 +1,61 @@
+// Copyright 2026 The frp Authors
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package visitor
+
+import (
+	"net"
+	"testing"
+	"time"
+
+	"github.com/stretchr/testify/require"
+
+	"github.com/fatedier/frp/pkg/proto/wire"
+	"github.com/fatedier/frp/pkg/util/util"
+)
+
+func TestManagerNewConnCarriesWireProtocol(t *testing.T) {
+	vm := NewManager()
+	listener, err := vm.Listen("sudp", "secret", []string{"*"})
+	require.NoError(t, err)
+	defer listener.Close()
+
+	client, server := net.Pipe()
+	defer client.Close()
+	defer server.Close()
+
+	now := time.Now().Unix()
+	errCh := make(chan error, 1)
+	go func() {
+		errCh <- vm.NewConn(
+			"sudp",
+			server,
+			now,
+			util.GetAuthKey("secret", now),
+			false,
+			false,
+			"user",
+			wire.ProtocolV2,
+		)
+	}()
+
+	acceptedConn, err := listener.Accept()
+	require.NoError(t, err)
+	defer acceptedConn.Close()
+
+	getter, ok := acceptedConn.(interface{ WireProtocol() string })
+	require.True(t, ok)
+	require.Equal(t, wire.ProtocolV2, getter.WireProtocol())
+	require.NoError(t, <-errCh)
+}