xtcp: when connection timeout occurs, support fallback to STCP (#3460)

client/service.go

@@ -369,7 +369,8 @@ func (cm *ConnectionManager) OpenConnection() error {
 		}
 		tlsConfig.NextProtos = []string{"frp"}
 
-		conn, err := quic.DialAddr(
+		conn, err := quic.DialAddrContext(
+			cm.ctx,
 			net.JoinHostPort(cm.cfg.ServerAddr, strconv.Itoa(cm.cfg.ServerPort)),
 			tlsConfig, &quic.Config{
 				MaxIdleTimeout:     time.Duration(cm.cfg.QUICMaxIdleTimeout) * time.Second,
@@ -467,7 +468,8 @@ func (cm *ConnectionManager) realConnect() (net.Conn, error) {
 			Hook: utilnet.DialHookCustomTLSHeadByte(tlsConfig != nil, cm.cfg.DisableCustomTLSFirstByte),
 		}),
 	)
-	conn, err := libdial.Dial(
+	conn, err := libdial.DialContext(
+		cm.ctx,
 		net.JoinHostPort(cm.cfg.ServerAddr, strconv.Itoa(cm.cfg.ServerPort)),
 		dialOptions...,
 	)

client/visitor/stcp.go

@@ -35,17 +35,20 @@ type STCPVisitor struct {
 }
 
 func (sv *STCPVisitor) Run() (err error) {
-	sv.l, err = net.Listen("tcp", net.JoinHostPort(sv.cfg.BindAddr, strconv.Itoa(sv.cfg.BindPort)))
+	if sv.cfg.BindPort > 0 {
-	if err != nil {
+		sv.l, err = net.Listen("tcp", net.JoinHostPort(sv.cfg.BindAddr, strconv.Itoa(sv.cfg.BindPort)))
-		return
+		if err != nil {
+			return
+		}
+		go sv.worker()
 	}
 
-	go sv.worker()
+	go sv.internalConnWorker()
 	return
 }
 
 func (sv *STCPVisitor) Close() {
-	sv.l.Close()
+	sv.BaseVisitor.Close()
 }
 
 func (sv *STCPVisitor) worker() {
@@ -56,7 +59,18 @@ func (sv *STCPVisitor) worker() {
 			xl.Warn("stcp local listener closed")
 			return
 		}
+		go sv.handleConn(conn)
+	}
+}
 
+func (sv *STCPVisitor) internalConnWorker() {
+	xl := xlog.FromContextSafe(sv.ctx)
+	for {
+		conn, err := sv.internalLn.Accept()
+		if err != nil {
+			xl.Warn("stcp internal listener closed")
+			return
+		}
 		go sv.handleConn(conn)
 	}
 }

client/visitor/sudp.go

@@ -254,6 +254,7 @@ func (sv *SUDPVisitor) Close() {
 	default:
 		close(sv.checkCloseCh)
 	}
+	sv.BaseVisitor.Close()
 	if sv.udpConn != nil {
 		sv.udpConn.Close()
 	}

client/visitor/visitor.go

@@ -21,12 +21,14 @@ import (
 
 	"github.com/fatedier/frp/pkg/config"
 	"github.com/fatedier/frp/pkg/transport"
+	utilnet "github.com/fatedier/frp/pkg/util/net"
 	"github.com/fatedier/frp/pkg/util/xlog"
 )
 
 // Visitor is used for forward traffics from local port tot remote service.
 type Visitor interface {
 	Run() error
+	AcceptConn(conn net.Conn) error
 	Close()
 }
 
@@ -35,14 +37,17 @@ func NewVisitor(
 	cfg config.VisitorConf,
 	clientCfg config.ClientCommonConf,
 	connectServer func() (net.Conn, error),
+	transferConn func(string, net.Conn) error,
 	msgTransporter transport.MessageTransporter,
 ) (visitor Visitor) {
 	xl := xlog.FromContextSafe(ctx).Spawn().AppendPrefix(cfg.GetBaseInfo().ProxyName)
 	baseVisitor := BaseVisitor{
 		clientCfg:      clientCfg,
 		connectServer:  connectServer,
+		transferConn:   transferConn,
 		msgTransporter: msgTransporter,
 		ctx:            xlog.NewContext(ctx, xl),
+		internalLn:     utilnet.NewInternalListener(),
 	}
 	switch cfg := cfg.(type) {
 	case *config.STCPVisitorConf:
@@ -69,9 +74,24 @@ func NewVisitor(
 type BaseVisitor struct {
 	clientCfg      config.ClientCommonConf
 	connectServer  func() (net.Conn, error)
+	transferConn   func(string, net.Conn) error
 	msgTransporter transport.MessageTransporter
 	l              net.Listener
+	internalLn     *utilnet.InternalListener
 
 	mu  sync.RWMutex
 	ctx context.Context
 }
+
+func (v *BaseVisitor) AcceptConn(conn net.Conn) error {
+	return v.internalLn.PutConn(conn)
+}
+
+func (v *BaseVisitor) Close() {
+	if v.l != nil {
+		v.l.Close()
+	}
+	if v.internalLn != nil {
+		v.internalLn.Close()
+	}
+}

client/visitor/visitor_manager.go

@@ -16,6 +16,7 @@ package visitor
 
 import (
 	"context"
+	"fmt"
 	"net"
 	"sync"
 	"time"
@@ -34,7 +35,7 @@ type Manager struct {
 
 	checkInterval time.Duration
 
-	mu  sync.Mutex
+	mu  sync.RWMutex
 	ctx context.Context
 
 	stopCh chan struct{}
@@ -83,11 +84,24 @@ func (vm *Manager) Run() {
 	}
 }
 
+func (vm *Manager) Close() {
+	vm.mu.Lock()
+	defer vm.mu.Unlock()
+	for _, v := range vm.visitors {
+		v.Close()
+	}
+	select {
+	case <-vm.stopCh:
+	default:
+		close(vm.stopCh)
+	}
+}
+
 // Hold lock before calling this function.
 func (vm *Manager) startVisitor(cfg config.VisitorConf) (err error) {
 	xl := xlog.FromContextSafe(vm.ctx)
 	name := cfg.GetBaseInfo().ProxyName
-	visitor := NewVisitor(vm.ctx, cfg, vm.clientCfg, vm.connectServer, vm.msgTransporter)
+	visitor := NewVisitor(vm.ctx, cfg, vm.clientCfg, vm.connectServer, vm.TransferConn, vm.msgTransporter)
 	err = visitor.Run()
 	if err != nil {
 		xl.Warn("start error: %v", err)
@@ -139,15 +153,13 @@ func (vm *Manager) Reload(cfgs map[string]config.VisitorConf) {
 	}
 }
 
-func (vm *Manager) Close() {
+// TransferConn transfers a connection to a visitor.
-	vm.mu.Lock()
+func (vm *Manager) TransferConn(name string, conn net.Conn) error {
-	defer vm.mu.Unlock()
+	vm.mu.RLock()
-	for _, v := range vm.visitors {
+	defer vm.mu.RUnlock()
-		v.Close()
+	v, ok := vm.visitors[name]
-	}
+	if !ok {
-	select {
+		return fmt.Errorf("visitor [%s] not found", name)
-	case <-vm.stopCh:
-	default:
-		close(vm.stopCh)
 	}
+	return v.AcceptConn(conn)
 }

client/visitor/xtcp.go

@@ -59,12 +59,15 @@ func (sv *XTCPVisitor) Run() (err error) {
 		sv.session = NewQUICTunnelSession(&sv.clientCfg)
 	}
 
-	sv.l, err = net.Listen("tcp", net.JoinHostPort(sv.cfg.BindAddr, strconv.Itoa(sv.cfg.BindPort)))
+	if sv.cfg.BindPort > 0 {
-	if err != nil {
+		sv.l, err = net.Listen("tcp", net.JoinHostPort(sv.cfg.BindAddr, strconv.Itoa(sv.cfg.BindPort)))
-		return
+		if err != nil {
+			return
+		}
+		go sv.worker()
 	}
 
-	go sv.worker()
+	go sv.internalConnWorker()
 	go sv.processTunnelStartEvents()
 	if sv.cfg.KeepTunnelOpen {
 		sv.retryLimiter = rate.NewLimiter(rate.Every(time.Hour/time.Duration(sv.cfg.MaxRetriesAnHour)), sv.cfg.MaxRetriesAnHour)
@@ -74,8 +77,12 @@ func (sv *XTCPVisitor) Run() (err error) {
 }
 
 func (sv *XTCPVisitor) Close() {
-	sv.l.Close()
+	sv.mu.Lock()
-	sv.cancel()
+	defer sv.mu.Unlock()
+	sv.BaseVisitor.Close()
+	if sv.cancel != nil {
+		sv.cancel()
+	}
 	if sv.session != nil {
 		sv.session.Close()
 	}
@@ -89,7 +96,18 @@ func (sv *XTCPVisitor) worker() {
 			xl.Warn("xtcp local listener closed")
 			return
 		}
+		go sv.handleConn(conn)
+	}
+}
 
+func (sv *XTCPVisitor) internalConnWorker() {
+	xl := xlog.FromContextSafe(sv.ctx)
+	for {
+		conn, err := sv.internalLn.Accept()
+		if err != nil {
+			xl.Warn("xtcp internal listener closed")
+			return
+		}
 		go sv.handleConn(conn)
 	}
 }
@@ -139,15 +157,37 @@ func (sv *XTCPVisitor) keepTunnelOpenWorker() {
 
 func (sv *XTCPVisitor) handleConn(userConn net.Conn) {
 	xl := xlog.FromContextSafe(sv.ctx)
-	defer userConn.Close()
+	isConnTrasfered := false
+	defer func() {
+		if !isConnTrasfered {
+			userConn.Close()
+		}
+	}()
 
 	xl.Debug("get a new xtcp user connection")
 
 	// Open a tunnel connection to the server. If there is already a successful hole-punching connection,
 	// it will be reused. Otherwise, it will block and wait for a successful hole-punching connection until timeout.
-	tunnelConn, err := sv.openTunnel()
+	ctx := context.Background()
+	if sv.cfg.FallbackTo != "" {
+		timeoutCtx, cancel := context.WithTimeout(ctx, time.Duration(sv.cfg.FallbackTimeoutMs)*time.Millisecond)
+		defer cancel()
+		ctx = timeoutCtx
+	}
+	tunnelConn, err := sv.openTunnel(ctx)
 	if err != nil {
 		xl.Error("open tunnel error: %v", err)
+		// no fallback, just return
+		if sv.cfg.FallbackTo == "" {
+			return
+		}
+
+		xl.Debug("try to transfer connection to visitor: %s", sv.cfg.FallbackTo)
+		if err := sv.transferConn(sv.cfg.FallbackTo, userConn); err != nil {
+			xl.Error("transfer connection to visitor %s error: %v", sv.cfg.FallbackTo, err)
+			return
+		}
+		isConnTrasfered = true
 		return
 	}
 
@@ -171,7 +211,7 @@ func (sv *XTCPVisitor) handleConn(userConn net.Conn) {
 }
 
 // openTunnel will open a tunnel connection to the target server.
-func (sv *XTCPVisitor) openTunnel() (conn net.Conn, err error) {
+func (sv *XTCPVisitor) openTunnel(ctx context.Context) (conn net.Conn, err error) {
 	xl := xlog.FromContextSafe(sv.ctx)
 	ticker := time.NewTicker(500 * time.Millisecond)
 	defer ticker.Stop()
@@ -185,6 +225,8 @@ func (sv *XTCPVisitor) openTunnel() (conn net.Conn, err error) {
 		select {
 		case <-sv.ctx.Done():
 			return nil, sv.ctx.Err()
+		case <-ctx.Done():
+			return nil, ctx.Err()
 		case <-immediateTrigger:
 			conn, err = sv.getTunnelConn()
 		case <-ticker.C:

cmd/frpc/sub/root.go

@@ -117,7 +117,6 @@ var rootCmd = &cobra.Command{
 		// Do not show command usage here.
 		err := runClient(cfgFile)
 		if err != nil {
-			fmt.Println(err)
 			os.Exit(1)
 		}
 		return nil
@@ -199,6 +198,7 @@ func parseClientCommonCfgFromCmd() (cfg config.ClientCommonConf, err error) {
 func runClient(cfgFilePath string) error {
 	cfg, pxyCfgs, visitorCfgs, err := config.ParseClientConfig(cfgFilePath)
 	if err != nil {
+		fmt.Println(err)
 		return err
 	}
 	return startService(cfg, pxyCfgs, visitorCfgs, cfgFilePath)
@@ -214,8 +214,8 @@ func startService(
 		cfg.LogMaxDays, cfg.DisableLogColor)
 
 	if cfgFile != "" {
-		log.Trace("start frpc service for config file [%s]", cfgFile)
+		log.Info("start frpc service for config file [%s]", cfgFile)
-		defer log.Trace("frpc service for config file [%s] stopped", cfgFile)
+		defer log.Info("frpc service for config file [%s] stopped", cfgFile)
 	}
 	svr, errRet := client.NewService(cfg, pxyCfgs, visitorCfgs, cfgFile)
 	if errRet != nil {

conf/frpc_full.ini

@@ -337,6 +337,8 @@ server_name = secret_tcp
 sk = abcdefg
 # connect this address to visitor stcp server
 bind_addr = 127.0.0.1
+# bind_port can be less than 0, it means don't bind to the port and only receive connections redirected from
+# other visitors. (This is not supported for SUDP now)
 bind_port = 9000
 use_encryption = false
 use_compression = false
@@ -355,6 +357,8 @@ type = xtcp
 server_name = p2p_tcp
 sk = abcdefg
 bind_addr = 127.0.0.1
+# bind_port can be less than 0, it means don't bind to the port and only receive connections redirected from
+# other visitors. (This is not supported for SUDP now)
 bind_port = 9001
 use_encryption = false
 use_compression = false
@@ -363,6 +367,8 @@ keep_tunnel_open = false
 # effective when keep_tunnel_open is set to true, the number of attempts to punch through per hour
 max_retries_an_hour = 8
 min_retry_interval = 90
+# fallback_to = stcp_visitor
+# fallback_timeout_ms = 500
 
 [tcpmuxhttpconnect]
 type = tcpmux

pkg/config/client_test.go

@@ -661,9 +661,10 @@ func Test_LoadClientBasicConf(t *testing.T) {
 				BindAddr:   "127.0.0.1",
 				BindPort:   9001,
 			},
-			Protocol:         "quic",
+			Protocol:          "quic",
-			MaxRetriesAnHour: 8,
+			MaxRetriesAnHour:  8,
-			MinRetryInterval: 90,
+			MinRetryInterval:  90,
+			FallbackTimeoutMs: 1000,
 		},
 	}
 

pkg/config/visitor.go

@@ -49,7 +49,10 @@ type BaseVisitorConf struct {
 	Sk             string `ini:"sk" json:"sk"`
 	ServerName     string `ini:"server_name" json:"server_name"`
 	BindAddr       string `ini:"bind_addr" json:"bind_addr"`
-	BindPort       int    `ini:"bind_port" json:"bind_port"`
+	// BindPort is the port that visitor listens on.
+	// It can be less than 0, it means don't bind to the port and only receive connections redirected from
+	// other visitors. (This is not supported for SUDP now)
+	BindPort int `ini:"bind_port" json:"bind_port"`
 }
 
 type SUDPVisitorConf struct {
@@ -63,10 +66,12 @@ type STCPVisitorConf struct {
 type XTCPVisitorConf struct {
 	BaseVisitorConf `ini:",extends"`
 
-	Protocol         string `ini:"protocol" json:"protocol,omitempty"`
+	Protocol          string `ini:"protocol" json:"protocol,omitempty"`
-	KeepTunnelOpen   bool   `ini:"keep_tunnel_open" json:"keep_tunnel_open,omitempty"`
+	KeepTunnelOpen    bool   `ini:"keep_tunnel_open" json:"keep_tunnel_open,omitempty"`
-	MaxRetriesAnHour int    `ini:"max_retries_an_hour" json:"max_retries_an_hour,omitempty"`
+	MaxRetriesAnHour  int    `ini:"max_retries_an_hour" json:"max_retries_an_hour,omitempty"`
-	MinRetryInterval int    `ini:"min_retry_interval" json:"min_retry_interval,omitempty"`
+	MinRetryInterval  int    `ini:"min_retry_interval" json:"min_retry_interval,omitempty"`
+	FallbackTo        string `ini:"fallback_to" json:"fallback_to,omitempty"`
+	FallbackTimeoutMs int    `ini:"fallback_timeout_ms" json:"fallback_timeout_ms,omitempty"`
 }
 
 // DefaultVisitorConf creates a empty VisitorConf object by visitorType.
@@ -134,7 +139,9 @@ func (cfg *BaseVisitorConf) check() (err error) {
 		err = fmt.Errorf("bind_addr shouldn't be empty")
 		return
 	}
-	if cfg.BindPort <= 0 {
+	// BindPort can be less than 0, it means don't bind to the port and only receive connections redirected from
+	// other visitors
+	if cfg.BindPort == 0 {
 		err = fmt.Errorf("bind_port is required")
 		return
 	}
@@ -155,7 +162,6 @@ func (cfg *BaseVisitorConf) unmarshalFromIni(prefix string, name string, section
 	if cfg.BindAddr == "" {
 		cfg.BindAddr = "127.0.0.1"
 	}
-
 	return nil
 }
 
@@ -169,7 +175,6 @@ func preVisitorUnmarshalFromIni(cfg VisitorConf, prefix string, name string, sec
 	if err != nil {
 		return err
 	}
-
 	return nil
 }
 
@@ -268,7 +273,9 @@ func (cfg *XTCPVisitorConf) Compare(cmp VisitorConf) bool {
 	if cfg.Protocol != cmpConf.Protocol ||
 		cfg.KeepTunnelOpen != cmpConf.KeepTunnelOpen ||
 		cfg.MaxRetriesAnHour != cmpConf.MaxRetriesAnHour ||
-		cfg.MinRetryInterval != cmpConf.MinRetryInterval {
+		cfg.MinRetryInterval != cmpConf.MinRetryInterval ||
+		cfg.FallbackTo != cmpConf.FallbackTo ||
+		cfg.FallbackTimeoutMs != cmpConf.FallbackTimeoutMs {
 		return false
 	}
 	return true
@@ -290,6 +297,9 @@ func (cfg *XTCPVisitorConf) UnmarshalFromIni(prefix string, name string, section
 	if cfg.MinRetryInterval <= 0 {
 		cfg.MinRetryInterval = 90
 	}
+	if cfg.FallbackTimeoutMs <= 0 {
+		cfg.FallbackTimeoutMs = 1000
+	}
 	return
 }
 

pkg/config/visitor_test.go

@@ -87,9 +87,10 @@ func Test_Visitor_UnmarshalFromIni(t *testing.T) {
 					BindAddr:   "127.0.0.1",
 					BindPort:   9001,
 				},
-				Protocol:         "quic",
+				Protocol:          "quic",
-				MaxRetriesAnHour: 8,
+				MaxRetriesAnHour:  8,
-				MinRetryInterval: 90,
+				MinRetryInterval:  90,
+				FallbackTimeoutMs: 1000,
 			},
 		},
 	}

pkg/nathole/analysis.go

@@ -63,20 +63,20 @@ var (
 	}
 
 	// mode 2, HardNAT is receiver, EasyNAT is sender
-	// sender, portsRandomNumber 1000, sendDelayMs 2000 | receiver, listen 256 ports, ttl 7
+	// sender, portsRandomNumber 1000, sendDelayMs 3000 | receiver, listen 256 ports, ttl 7
-	// sender, portsRandomNumber 1000, sendDelayMs 2000 | receiver, listen 256 ports, ttl 4
+	// sender, portsRandomNumber 1000, sendDelayMs 3000 | receiver, listen 256 ports, ttl 4
-	// sender, portsRandomNumber 1000, sendDelayMs 2000 | receiver, listen 256 ports
+	// sender, portsRandomNumber 1000, sendDelayMs 3000 | receiver, listen 256 ports
 	mode2Behaviors = []lo.Tuple2[RecommandBehavior, RecommandBehavior]{
 		lo.T2(
-			RecommandBehavior{Role: DetectRoleSender, PortsRandomNumber: 1000, SendDelayMs: 2000},
+			RecommandBehavior{Role: DetectRoleSender, PortsRandomNumber: 1000, SendDelayMs: 3000},
 			RecommandBehavior{Role: DetectRoleReceiver, ListenRandomPorts: 256, TTL: 7},
 		),
 		lo.T2(
-			RecommandBehavior{Role: DetectRoleSender, PortsRandomNumber: 1000, SendDelayMs: 2000},
+			RecommandBehavior{Role: DetectRoleSender, PortsRandomNumber: 1000, SendDelayMs: 3000},
 			RecommandBehavior{Role: DetectRoleReceiver, ListenRandomPorts: 256, TTL: 4},
 		),
 		lo.T2(
-			RecommandBehavior{Role: DetectRoleSender, PortsRandomNumber: 1000, SendDelayMs: 2000},
+			RecommandBehavior{Role: DetectRoleSender, PortsRandomNumber: 1000, SendDelayMs: 3000},
 			RecommandBehavior{Role: DetectRoleReceiver, ListenRandomPorts: 256},
 		),
 	}
@@ -98,21 +98,21 @@ var (
 	}
 
 	// mode 4, Regular ports changes are usually the sender.
-	// sender, portsRandomNumber 1000, sendDelayMs: 2000 | receiver, listen 256 ports, ttl 7, portsRangeNumber 10
+	// sender, portsRandomNumber 1000, sendDelayMs: 2000 | receiver, listen 256 ports, ttl 7, portsRangeNumber 2
-	// sender, portsRandomNumber 1000, sendDelayMs: 2000 | receiver, listen 256 ports, ttl 4, portsRangeNumber 10
+	// sender, portsRandomNumber 1000, sendDelayMs: 2000 | receiver, listen 256 ports, ttl 4, portsRangeNumber 2
-	// sender, portsRandomNumber 1000, SendDelayMs: 2000 | receiver, listen 256 ports, portsRangeNumber 10
+	// sender, portsRandomNumber 1000, SendDelayMs: 2000 | receiver, listen 256 ports, portsRangeNumber 2
 	mode4Behaviors = []lo.Tuple2[RecommandBehavior, RecommandBehavior]{
 		lo.T2(
-			RecommandBehavior{Role: DetectRoleSender, PortsRandomNumber: 1000, SendDelayMs: 2000},
+			RecommandBehavior{Role: DetectRoleSender, PortsRandomNumber: 1000, SendDelayMs: 3000},
-			RecommandBehavior{Role: DetectRoleReceiver, ListenRandomPorts: 256, TTL: 7, PortsRangeNumber: 10},
+			RecommandBehavior{Role: DetectRoleReceiver, ListenRandomPorts: 256, TTL: 7, PortsRangeNumber: 2},
 		),
 		lo.T2(
-			RecommandBehavior{Role: DetectRoleSender, PortsRandomNumber: 1000, SendDelayMs: 2000},
+			RecommandBehavior{Role: DetectRoleSender, PortsRandomNumber: 1000, SendDelayMs: 3000},
-			RecommandBehavior{Role: DetectRoleReceiver, ListenRandomPorts: 256, TTL: 4, PortsRangeNumber: 10},
+			RecommandBehavior{Role: DetectRoleReceiver, ListenRandomPorts: 256, TTL: 4, PortsRangeNumber: 2},
 		),
 		lo.T2(
-			RecommandBehavior{Role: DetectRoleSender, PortsRandomNumber: 1000, SendDelayMs: 2000},
+			RecommandBehavior{Role: DetectRoleSender, PortsRandomNumber: 1000, SendDelayMs: 3000},
-			RecommandBehavior{Role: DetectRoleReceiver, ListenRandomPorts: 256, PortsRangeNumber: 10},
+			RecommandBehavior{Role: DetectRoleReceiver, ListenRandomPorts: 256, PortsRangeNumber: 2},
 		),
 	}
 )

pkg/nathole/classify.go

@@ -85,11 +85,6 @@ func ClassifyNATFeature(addresses []string, localIPs []string) (*NatFeature, err
 		}
 	}
 
-	natFeature.PortsDifference = portMax - portMin
-	if natFeature.PortsDifference <= 10 && natFeature.PortsDifference >= 1 {
-		natFeature.RegularPortsChange = true
-	}
-
 	switch {
 	case ipChanged && portChanged:
 		natFeature.NatType = HardNAT
@@ -104,6 +99,12 @@ func ClassifyNATFeature(addresses []string, localIPs []string) (*NatFeature, err
 		natFeature.NatType = EasyNAT
 		natFeature.Behavior = BehaviorNoChange
 	}
+	if natFeature.Behavior == BehaviorPortChanged {
+		natFeature.PortsDifference = portMax - portMin
+		if natFeature.PortsDifference <= 5 && natFeature.PortsDifference >= 1 {
+			natFeature.RegularPortsChange = true
+		}
+	}
 	return natFeature, nil
 }
 

pkg/nathole/nathole.go

@@ -384,7 +384,7 @@ func sendSidMessageToRangePorts(
 				if err := sendFunc(conn, detectAddr); err != nil {
 					xl.Trace("send sid message from %s to %s error: %v", conn.LocalAddr(), detectAddr, err)
 				}
-				time.Sleep(5 * time.Millisecond)
+				time.Sleep(2 * time.Millisecond)
 			}
 		}
 	}

test/e2e/basic/basic.go

@@ -376,7 +376,7 @@ var _ = ginkgo.Describe("[Feature: Basic]", func() {
 				for _, test := range tests {
 					framework.NewRequestExpect(f).
 						RequestModify(func(r *request.Request) {
-							r.Timeout(5 * time.Second)
+							r.Timeout(10 * time.Second)
 						}).
 						Protocol(protocol).
 						PortName(test.bindPortName).

test/e2e/basic/xtcp.go

@@ -0,0 +1,52 @@
+package basic
+
+import (
+	"fmt"
+	"time"
+
+	"github.com/onsi/ginkgo/v2"
+
+	"github.com/fatedier/frp/test/e2e/framework"
+	"github.com/fatedier/frp/test/e2e/framework/consts"
+	"github.com/fatedier/frp/test/e2e/pkg/port"
+	"github.com/fatedier/frp/test/e2e/pkg/request"
+)
+
+var _ = ginkgo.Describe("[Feature: XTCP]", func() {
+	f := framework.NewDefaultFramework()
+
+	ginkgo.It("Fallback To STCP", func() {
+		serverConf := consts.DefaultServerConfig
+		clientConf := consts.DefaultClientConfig
+
+		bindPortName := port.GenName("XTCP")
+		clientConf += fmt.Sprintf(`
+			[foo]
+			type = stcp
+			local_port = {{ .%s }}
+
+			[foo-visitor]
+			type = stcp
+			role = visitor
+			server_name = foo
+			bind_port = -1
+
+			[bar-visitor]
+			type = xtcp
+			role = visitor
+			server_name = bar
+			bind_port = {{ .%s }}
+			keep_tunnel_open = true
+			fallback_to = foo-visitor
+			fallback_timeout_ms = 200
+			`, framework.TCPEchoServerPort, bindPortName)
+
+		f.RunProcesses([]string{serverConf}, []string{clientConf})
+		framework.NewRequestExpect(f).
+			RequestModify(func(r *request.Request) {
+				r.Timeout(time.Second)
+			}).
+			PortName(bindPortName).
+			Ensure()
+	})
+})