fix(tunnel): resolve UDP stream interruption and add KCP protocol support

- Increase UDP listener default TTL from 5s to 30s to prevent idle disconnect
- Add mux keepalive config (15s interval, 45s timeout) to tunnel relay handler
- Add KCP as tunnel chain transport protocol with keepalive and UDP mode default
- Add KCP protocol option to tunnel UI (frontend)
- Remove generic 'tcp' fallback key from KCP metadata to prevent false TCP mode
- Simplify forward service config by removing unused tunnelTLSProtocol parameter

go-backend/internal/http/handler/control_plane.go

@@ -185,14 +185,6 @@ func (h *Handler) listForwardPorts(forwardID int64) ([]forwardPortRecord, error)
 	return h.repo.ListForwardPorts(forwardID)
 }
 
-func (h *Handler) isTunnelSelectedTLSProtocol(tunnelID int64) (bool, error) {
-	protocol, err := h.repo.GetTunnelOutProtocol(tunnelID)
-	if err != nil {
-		return false, err
-	}
-	return isTLSTunnelProtocol(protocol), nil
-}
-
 func (h *Handler) getNodeRecord(nodeID int64) (*nodeRecord, error) {
 	n, err := h.repo.GetNodeRecord(nodeID)
 	if err != nil {
@@ -272,10 +264,6 @@ func (h *Handler) syncForwardServicesWithWarnings(forward *forwardRecord, method
 	}
 
 	serviceBase := buildForwardServiceBaseWithResolvedUserTunnel(forward.ID, forward.UserID, userTunnelID)
-	tunnelTLSProtocol, err := h.isTunnelSelectedTLSProtocol(forward.TunnelID)
-	if err != nil {
-		return nil, err
-	}
 
 	for _, fp := range ports {
 		if limiterID != nil && speed != nil {
@@ -298,7 +286,7 @@ func (h *Handler) syncForwardServicesWithWarnings(forward *forwardRecord, method
 		if err != nil {
 			return nil, err
 		}
-		services := buildForwardServiceConfigs(serviceBase, forward, tunnel, node, fp.Port, strings.TrimSpace(fp.InIP), limiterID, tunnelTLSProtocol)
+		services := buildForwardServiceConfigs(serviceBase, forward, tunnel, node, fp.Port, strings.TrimSpace(fp.InIP), limiterID)
 		_, err = h.sendNodeCommand(node.ID, method, services, true, false)
 		if err != nil && allowFallbackAdd && method == "UpdateService" {
 			if isNotFoundError(err) {
@@ -313,7 +301,7 @@ func (h *Handler) syncForwardServicesWithWarnings(forward *forwardRecord, method
 		}
 		if err != nil && strings.EqualFold(strings.TrimSpace(method), "UpdateService") && isCannotAssignRequestedAddressError(err) {
 			var warning string
-			warning, err = h.fallbackForwardPortToDefaultBind(forward, tunnel, node, fp, serviceBase, limiterID, tunnelTLSProtocol)
+			warning, err = h.fallbackForwardPortToDefaultBind(forward, tunnel, node, fp, serviceBase, limiterID)
 			if err == nil && warning != "" {
 				warnings = append(warnings, warning)
 			}
@@ -339,7 +327,7 @@ func (h *Handler) syncForwardServicesWithWarnings(forward *forwardRecord, method
 	return warnings, nil
 }
 
-func (h *Handler) fallbackForwardPortToDefaultBind(forward *forwardRecord, tunnel *tunnelRecord, node *nodeRecord, fp forwardPortRecord, serviceBase string, limiterID *int64, tunnelTLSProtocol bool) (string, error) {
+func (h *Handler) fallbackForwardPortToDefaultBind(forward *forwardRecord, tunnel *tunnelRecord, node *nodeRecord, fp forwardPortRecord, serviceBase string, limiterID *int64) (string, error) {
 	if h == nil || forward == nil || tunnel == nil || node == nil {
 		return "", errors.New("invalid bind fallback context")
 	}
@@ -356,7 +344,7 @@ func (h *Handler) fallbackForwardPortToDefaultBind(forward *forwardRecord, tunne
 	}
 
 	time.Sleep(150 * time.Millisecond)
-	defaultServices := buildForwardServiceConfigs(serviceBase, forward, tunnel, node, fp.Port, "", limiterID, tunnelTLSProtocol)
+	defaultServices := buildForwardServiceConfigs(serviceBase, forward, tunnel, node, fp.Port, "", limiterID)
 	if _, err := h.sendNodeCommand(node.ID, "AddService", defaultServices, true, false); err != nil {
 		return "", err
 	}
@@ -1561,7 +1549,7 @@ func compactErrorMessage(msg string) string {
 	return strings.Join(strings.Fields(strings.ToLower(msg)), "")
 }
 
-func buildForwardServiceConfigs(baseName string, forward *forwardRecord, tunnel *tunnelRecord, node *nodeRecord, port int, bindIP string, limiterID *int64, tunnelTLSProtocol bool) []map[string]interface{} {
+func buildForwardServiceConfigs(baseName string, forward *forwardRecord, tunnel *tunnelRecord, node *nodeRecord, port int, bindIP string, limiterID *int64) []map[string]interface{} {
 	protocols := []string{"tcp", "udp"}
 	services := make([]map[string]interface{}, 0, 2)
 	targets := splitRemoteTargets(forward.RemoteAddr)
@@ -1605,9 +1593,9 @@ func buildForwardServiceConfigs(baseName string, forward *forwardRecord, tunnel
 			},
 		}
 		if protocol == "udp" {
-			listenerMetadata := map[string]interface{}{"keepAlive": true}
-			if tunnelTLSProtocol {
-				listenerMetadata["ttl"] = "10s"
+			listenerMetadata := map[string]interface{}{
+				"keepAlive": true,
+				"ttl":       "30s",
 			}
 			service["listener"].(map[string]interface{})["metadata"] = listenerMetadata
 		}

go-backend/internal/http/handler/control_plane_test.go

@@ -378,7 +378,7 @@ func TestRetryTunnelServiceAddWithCleanupReturnsCleanupError(t *testing.T) {
 func TestBuildForwardServiceConfigs_UsesBindIPForListen(t *testing.T) {
 	forward := &forwardRecord{RemoteAddr: "1.2.3.4:80", Strategy: "fifo", TunnelID: 7}
 	node := &nodeRecord{TCPListenAddr: "[::]", UDPListenAddr: "[::]"}
-	services := buildForwardServiceConfigs("1_2_0", forward, nil, node, 22000, "10.9.8.7", nil, false)
+	services := buildForwardServiceConfigs("1_2_0", forward, nil, node, 22000, "10.9.8.7", nil)
 	if len(services) != 2 {
 		t.Fatalf("expected 2 services, got %d", len(services))
 	}
@@ -393,7 +393,7 @@ func TestBuildForwardServiceConfigs_UsesBindIPForListen(t *testing.T) {
 func TestBuildForwardServiceConfigs_DefaultListenAddrWhenBindIPEmpty(t *testing.T) {
 	forward := &forwardRecord{RemoteAddr: "1.2.3.4:80", Strategy: "fifo", TunnelID: 7}
 	node := &nodeRecord{TCPListenAddr: "0.0.0.0", UDPListenAddr: "[::]"}
-	services := buildForwardServiceConfigs("1_2_0", forward, nil, node, 22001, "", nil, false)
+	services := buildForwardServiceConfigs("1_2_0", forward, nil, node, 22001, "", nil)
 	if len(services) != 2 {
 		t.Fatalf("expected 2 services, got %d", len(services))
 	}
@@ -409,7 +409,7 @@ func TestBuildForwardServiceConfigs_DefaultListenAddrWhenBindIPEmpty(t *testing.
 func TestBuildForwardServiceConfigs_BindIPAlreadyContainsPort(t *testing.T) {
 	forward := &forwardRecord{RemoteAddr: "1.2.3.4:80", Strategy: "fifo", TunnelID: 7}
 	node := &nodeRecord{TCPListenAddr: "[::]", UDPListenAddr: "[::]"}
-	services := buildForwardServiceConfigs("1_2_0", forward, nil, node, 55555, "3.3.3.3:12345", nil, false)
+	services := buildForwardServiceConfigs("1_2_0", forward, nil, node, 55555, "3.3.3.3:12345", nil)
 	if len(services) != 2 {
 		t.Fatalf("expected 2 services, got %d", len(services))
 	}
@@ -464,7 +464,7 @@ func TestBuildForwardServiceConfigs_IPv6BindIP(t *testing.T) {
 		t.Run(tt.name, func(t *testing.T) {
 			forward := &forwardRecord{RemoteAddr: "1.2.3.4:80", Strategy: "fifo", TunnelID: 7}
 			node := &nodeRecord{TCPListenAddr: "[::]", UDPListenAddr: "[::]"}
-			services := buildForwardServiceConfigs("1_2_0", forward, nil, node, tt.port, tt.bindIP, nil, false)
+			services := buildForwardServiceConfigs("1_2_0", forward, nil, node, tt.port, tt.bindIP, nil)
 			if len(services) != 2 {
 				t.Fatalf("expected 2 services, got %d", len(services))
 			}

go-backend/internal/http/handler/federation.go

@@ -144,17 +144,24 @@ type remoteUsageNodeItem struct {
 
 func buildFederationServiceConfig(serviceName, addr, protocol, role, chainName string, targetCount int, interfaceName string) map[string]interface{} {
 	service := map[string]interface{}{
-		"name": serviceName,
-		"addr": addr,
+		"name":     serviceName,
+		"addr":     addr,
 		"handler": map[string]interface{}{
 			"type": "relay",
 		},
-		"listener": map[string]interface{}{
-			"type": protocol,
-		},
+		"listener": buildTunnelListenerConfig(protocol),
 	}
-	if isTLSTunnelProtocol(protocol) {
-		service["handler"].(map[string]interface{})["metadata"] = map[string]interface{}{"nodelay": true}
+	if isTCPTunnelProtocol(protocol) {
+		service["handler"].(map[string]interface{})["metadata"] = map[string]interface{}{
+			"nodelay":               true,
+			"mux.keepaliveInterval": "15s",
+			"mux.keepaliveTimeout":  "45s",
+		}
+	}
+	if isKCPTunnelProtocol(protocol) {
+		service["handler"].(map[string]interface{})["metadata"] = map[string]interface{}{
+			"connectTimeout": "30s",
+		}
 	}
 	if role == "middle" {
 		service["handler"].(map[string]interface{})["chain"] = chainName
@@ -1095,16 +1102,23 @@ func (h *Handler) federationRuntimeApplyRole(w http.ResponseWriter, r *http.Requ
 			connector := map[string]interface{}{
 				"type": "relay",
 			}
-			if isTLSTunnelProtocol(targetProtocol) {
-				connector["metadata"] = map[string]interface{}{"nodelay": true}
+			if isTCPTunnelProtocol(targetProtocol) {
+				connector["metadata"] = map[string]interface{}{
+					"nodelay":               true,
+					"mux.keepaliveInterval": "15s",
+					"mux.keepaliveTimeout":  "45s",
+				}
+			}
+			if isKCPTunnelProtocol(targetProtocol) {
+				connector["metadata"] = map[string]interface{}{
+					"connectTimeout": "30s",
+				}
 			}
 			nodeItems = append(nodeItems, map[string]interface{}{
 				"name":      fmt.Sprintf("node_%d", i+1),
 				"addr":      processServerAddress(fmt.Sprintf("%s:%d", host, target.Port)),
 				"connector": connector,
-				"dialer": map[string]interface{}{
-					"type": targetProtocol,
-				},
+				"dialer":    buildTunnelDialerConfig(targetProtocol),
 			})
 		}
 

go-backend/internal/http/handler/mutations.go

@@ -3452,16 +3452,23 @@ func buildTunnelChainConfig(tunnelID int64, fromNodeID int64, targets []tunnelRu
 		connector := map[string]interface{}{
 			"type": "relay",
 		}
-		if isTLSTunnelProtocol(protocol) {
-			connector["metadata"] = map[string]interface{}{"nodelay": true}
+		connectorMetadata := map[string]interface{}{}
+		if isTCPTunnelProtocol(protocol) {
+			connectorMetadata["nodelay"] = true
+			connectorMetadata["mux.keepaliveInterval"] = "15s"
+			connectorMetadata["mux.keepaliveTimeout"] = "45s"
+		}
+		if isKCPTunnelProtocol(protocol) {
+			connectorMetadata["connectTimeout"] = "30s"
+		}
+		if len(connectorMetadata) > 0 {
+			connector["metadata"] = connectorMetadata
 		}
 		nodeItems = append(nodeItems, map[string]interface{}{
 			"name":      fmt.Sprintf("node_%d", idx+1),
 			"addr":      processServerAddress(fmt.Sprintf("%s:%d", host, port)),
 			"connector": connector,
-			"dialer": map[string]interface{}{
-				"type": protocol,
-			},
+			"dialer":    buildTunnelDialerConfig(protocol),
 		})
 	}
 
@@ -3493,19 +3500,26 @@ func buildTunnelChainServiceConfig(tunnelID int64, chainNode tunnelRuntimeNode,
 	handlerCfg := map[string]interface{}{
 		"type": "relay",
 	}
-	if isTLSTunnelProtocol(protocol) {
-		handlerCfg["metadata"] = map[string]interface{}{"nodelay": true}
+	handlerMetadata := map[string]interface{}{}
+	if isTCPTunnelProtocol(protocol) {
+		handlerMetadata["nodelay"] = true
+		handlerMetadata["mux.keepaliveInterval"] = "15s"
+		handlerMetadata["mux.keepaliveTimeout"] = "45s"
+	}
+	if isKCPTunnelProtocol(protocol) {
+		handlerMetadata["connectTimeout"] = "30s"
+	}
+	if len(handlerMetadata) > 0 {
+		handlerCfg["metadata"] = handlerMetadata
 	}
 	if nextHopCandidateCount > 1 {
 		handlerCfg["retries"] = nextHopCandidateCount - 1
 	}
 	service := map[string]interface{}{
-		"name":    fmt.Sprintf("%d_tls", tunnelID),
-		"addr":    processServerAddress(fmt.Sprintf("%s:%d", defaultString(strings.TrimSpace(chainNode.ConnectIP), node.TCPListenAddr), chainNode.Port)),
-		"handler": handlerCfg,
-		"listener": map[string]interface{}{
-			"type": protocol,
-		},
+		"name":     fmt.Sprintf("%d_%s", tunnelID, protocol),
+		"addr":     processServerAddress(fmt.Sprintf("%s:%d", defaultString(strings.TrimSpace(chainNode.ConnectIP), node.TCPListenAddr), chainNode.Port)),
+		"handler":  handlerCfg,
+		"listener": buildTunnelListenerConfig(protocol),
 	}
 	if chainNode.ChainType == 2 {
 		service["handler"].(map[string]interface{})["chain"] = fmt.Sprintf("chains_%d", tunnelID)
@@ -3588,10 +3602,45 @@ func nodeDisplayName(node *nodeRecord) string {
 	return fmt.Sprintf("node_%d", node.ID)
 }
 
+func isTCPTunnelProtocol(protocol string) bool {
+	p := strings.ToLower(strings.TrimSpace(defaultString(protocol, "tls")))
+	return p == "tls" || p == "mtls" || p == "mtcp"
+}
+
+func isKCPTunnelProtocol(protocol string) bool {
+	return strings.EqualFold(strings.TrimSpace(protocol), "kcp")
+}
+
 func isTLSTunnelProtocol(protocol string) bool {
 	return strings.EqualFold(strings.TrimSpace(defaultString(protocol, "tls")), "tls")
 }
 
+func buildTunnelDialerConfig(protocol string) map[string]interface{} {
+	dialer := map[string]interface{}{
+		"type": protocol,
+	}
+	if isKCPTunnelProtocol(protocol) {
+		dialer["metadata"] = map[string]interface{}{
+			"kcp.keepalive": 10,
+			"kcp.tcp":       false,
+		}
+	}
+	return dialer
+}
+
+func buildTunnelListenerConfig(protocol string) map[string]interface{} {
+	listener := map[string]interface{}{
+		"type": protocol,
+	}
+	if isKCPTunnelProtocol(protocol) {
+		listener["metadata"] = map[string]interface{}{
+			"kcp.keepalive": 10,
+			"kcp.tcp":       false,
+		}
+	}
+	return listener
+}
+
 func nodeSupportsV4(node *nodeRecord) bool {
 	if node == nil {
 		return false