fix(kcp): enable congestion control, add FEC, and fix remote node UDP diagnosis

- KCP: switch from fast3 to fast2 mode, enable FEC (10/3), enable
  congestion control (nc=0) for automatic rate adaptation
- go-gost/x: support kcp.nc metadata to override mode-initialized
  NoCongestion value in dialer and listener Init()
- Diagnosis: add udpPingViaRemoteNode, fix pingViaRemoteNode to
  dispatch based on protocol, add Protocol field to federation
  diagnose request structs

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

@@ -71,10 +71,11 @@ type RuntimeReleaseRoleRequest struct {
 }
 
 type RuntimeDiagnoseRequest struct {
-	IP      string `json:"ip"`
+	IP       string `json:"ip"`
-	Port    int    `json:"port"`
+	Port     int    `json:"port"`
-	Count   int    `json:"count"`
+	Count    int    `json:"count"`
-	Timeout int    `json:"timeout"`
+	Timeout  int    `json:"timeout"`
+	Protocol string `json:"protocol"`
 }
 
 type RuntimeNodeCommandRequest struct {

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

@@ -1402,10 +1402,37 @@ func (h *Handler) tcpPingViaRemoteNode(node *nodeRecord, ip string, port int, op
 
 	fc := client.NewFederationClientWithTimeout(options.commandTimeout)
 	return fc.Diagnose(remoteURL, remoteToken, h.federationLocalDomain(), client.RuntimeDiagnoseRequest{
-		IP:      strings.TrimSpace(ip),
+		IP:       strings.TrimSpace(ip),
-		Port:    port,
+		Port:     port,
-		Count:   4,
+		Count:    4,
-		Timeout: options.pingTimeoutMS,
+		Timeout:  options.pingTimeoutMS,
+		Protocol: "tcp",
+	})
+}
+
+func (h *Handler) udpPingViaRemoteNode(node *nodeRecord, ip string, port int, options diagnosisExecOptions) (map[string]interface{}, error) {
+	if node == nil {
+		return nil, errors.New("节点不存在")
+	}
+	remoteURL := strings.TrimSpace(node.RemoteURL)
+	remoteToken := strings.TrimSpace(node.RemoteToken)
+	if remoteURL == "" || remoteToken == "" {
+		return nil, errors.New("远程节点缺少共享配置")
+	}
+	if options.commandTimeout <= 0 {
+		options.commandTimeout = diagnosisCommandTimeout
+	}
+	if options.pingTimeoutMS <= 0 {
+		options.pingTimeoutMS = int(diagnosisCommandTimeout / time.Millisecond)
+	}
+
+	fc := client.NewFederationClientWithTimeout(options.commandTimeout)
+	return fc.Diagnose(remoteURL, remoteToken, h.federationLocalDomain(), client.RuntimeDiagnoseRequest{
+		IP:       strings.TrimSpace(ip),
+		Port:     port,
+		Count:    4,
+		Timeout:  options.pingTimeoutMS,
+		Protocol: "udp",
 	})
 }
 
@@ -1422,6 +1449,9 @@ func (h *Handler) pingViaNode(nodeID int64, ip string, port int, protocol string
 }
 
 func (h *Handler) pingViaRemoteNode(node *nodeRecord, ip string, port int, protocol string, options diagnosisExecOptions) (map[string]interface{}, error) {
+	if isUDPBasedProtocol(protocol) {
+		return h.udpPingViaRemoteNode(node, ip, port, options)
+	}
 	return h.tcpPingViaRemoteNode(node, ip, port, options)
 }
 

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

@@ -86,10 +86,11 @@ type federationRuntimeReleaseRoleRequest struct {
 }
 
 type federationRuntimeDiagnoseRequest struct {
-	IP      string `json:"ip"`
+	IP       string `json:"ip"`
-	Port    int    `json:"port"`
+	Port     int    `json:"port"`
-	Count   int    `json:"count"`
+	Count    int    `json:"count"`
-	Timeout int    `json:"timeout"`
+	Timeout  int    `json:"timeout"`
+	Protocol string `json:"protocol"`
 }
 
 type federationRuntimeCommandRequest struct {
@@ -1281,7 +1282,12 @@ func (h *Handler) federationRuntimeDiagnose(w http.ResponseWriter, r *http.Reque
 		commandTimeout = diagnosisCommandTimeout
 	}
 
-	res, err := h.sendNodeCommandWithTimeout(share.NodeID, "TcpPing", map[string]interface{}{
+	commandType := "TcpPing"
+	if isUDPBasedProtocol(req.Protocol) {
+		commandType = "UdpPing"
+	}
+
+	res, err := h.sendNodeCommandWithTimeout(share.NodeID, commandType, map[string]interface{}{
 		"ip":      req.IP,
 		"port":    req.Port,
 		"count":   req.Count,

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

@@ -3635,13 +3635,14 @@ func buildTunnelDialerConfig(protocol string) map[string]interface{} {
 		dialer["metadata"] = map[string]interface{}{
 			"kcp.keepalive":   10,
 			"kcp.tcp":         false,
-			"kcp.mode":        "fast3",
+			"kcp.mode":        "fast2",
 			"kcp.sndwnd":      2048,
 			"kcp.rcvwnd":      2048,
 			"kcp.mtu":         1400,
-			"kcp.datashard":   0,
+			"kcp.datashard":   10,
-			"kcp.parityshard": 0,
+			"kcp.parityshard": 3,
 			"kcp.nocomp":      true,
+			"kcp.nc":          0,
 		}
 	}
 	return dialer
@@ -3655,13 +3656,14 @@ func buildTunnelListenerConfig(protocol string) map[string]interface{} {
 		listener["metadata"] = map[string]interface{}{
 			"kcp.keepalive":   10,
 			"kcp.tcp":         false,
-			"kcp.mode":        "fast3",
+			"kcp.mode":        "fast2",
 			"kcp.sndwnd":      2048,
 			"kcp.rcvwnd":      2048,
 			"kcp.mtu":         1400,
-			"kcp.datashard":   0,
+			"kcp.datashard":   10,
-			"kcp.parityshard": 0,
+			"kcp.parityshard": 3,
 			"kcp.nocomp":      true,
+			"kcp.nc":          0,
 		}
 	}
 	return listener

go-gost/x/dialer/kcp/dialer.go

@@ -11,6 +11,7 @@ import (
 	"github.com/go-gost/core/logger"
 	md "github.com/go-gost/core/metadata"
 	kcp_util "github.com/go-gost/x/internal/util/kcp"
+	mdutil "github.com/go-gost/x/metadata/util"
 	"github.com/go-gost/x/registry"
 	"github.com/xtaci/kcp-go/v5"
 	"github.com/xtaci/smux"
@@ -48,6 +49,9 @@ func (d *kcpDialer) Init(md md.Metadata) (err error) {
 	}
 
 	d.md.config.Init()
+	if md != nil && md.IsExists("kcp.nc") {
+		d.md.config.NoCongestion = mdutil.GetInt(md, "kcp.nc")
+	}
 
 	return nil
 }

go-gost/x/listener/kcp/listener.go

@@ -15,6 +15,7 @@ import (
 	limiter_wrapper "github.com/go-gost/x/limiter/traffic/wrapper"
 	metrics "github.com/go-gost/x/metrics/wrapper"
 	stats "github.com/go-gost/x/observer/stats/wrapper"
+	mdutil "github.com/go-gost/x/metadata/util"
 	"github.com/go-gost/x/registry"
 	"github.com/xtaci/kcp-go/v5"
 	"github.com/xtaci/smux"
@@ -53,6 +54,9 @@ func (l *kcpListener) Init(md md.Metadata) (err error) {
 
 	config := l.md.config
 	config.Init()
+	if md != nil && md.IsExists("kcp.nc") {
+		config.NoCongestion = mdutil.GetInt(md, "kcp.nc")
+	}
 
 	var conn net.PacketConn
 	if config.TCP {