Add stun sniffer

common/sniff/stun.go

@@ -0,0 +1,24 @@
+package sniff
+
+import (
+	"context"
+	"encoding/binary"
+	"os"
+
+	"github.com/sagernet/sing-box/adapter"
+	C "github.com/sagernet/sing-box/constant"
+)
+
+func STUNMessage(ctx context.Context, packet []byte) (*adapter.InboundContext, error) {
+	pLen := len(packet)
+	if pLen < 20 {
+		return nil, os.ErrInvalid
+	}
+	if binary.BigEndian.Uint32(packet[4:8]) != 0x2112A442 {
+		return nil, os.ErrInvalid
+	}
+	if len(packet) < 20+int(binary.BigEndian.Uint16(packet[2:4])) {
+		return nil, os.ErrInvalid
+	}
+	return &adapter.InboundContext{Protocol: C.ProtocolSTUN}, nil
+}