frpc: support nathole discover (#3381)

pkg/nathole/classify.go

@@ -0,0 +1,74 @@
+// Copyright 2023 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 nathole
+
+import (
+	"fmt"
+	"net"
+)
+
+const (
+	EasyNAT = "EasyNAT"
+	HardNAT = "HardNAT"
+
+	BehaviorNoChange    = "BehaviorNoChange"
+	BehaviorIPChanged   = "BehaviorIPChanged"
+	BehaviorPortChanged = "BehaviorPortChanged"
+	BehaviorBothChanged = "BehaviorBothChanged"
+)
+
+// ClassifyNATType classify NAT type by given addresses.
+func ClassifyNATType(addresses []string) (string, string, error) {
+	if len(addresses) <= 1 {
+		return "", "", fmt.Errorf("not enough addresses")
+	}
+	ipChanged := false
+	portChanged := false
+
+	var baseIP, basePort string
+	for _, addr := range addresses {
+		ip, port, err := net.SplitHostPort(addr)
+		if err != nil {
+			return "", "", err
+		}
+		if baseIP == "" {
+			baseIP = ip
+			basePort = port
+			continue
+		}
+
+		if baseIP != ip {
+			ipChanged = true
+		}
+		if basePort != port {
+			portChanged = true
+		}
+
+		if ipChanged && portChanged {
+			break
+		}
+	}
+
+	switch {
+	case ipChanged && portChanged:
+		return HardNAT, BehaviorBothChanged, nil
+	case ipChanged:
+		return HardNAT, BehaviorIPChanged, nil
+	case portChanged:
+		return HardNAT, BehaviorPortChanged, nil
+	default:
+		return EasyNAT, BehaviorNoChange, nil
+	}
+}