Add native protocol service plugins

plugins/services/dns_shared.go

@@ -0,0 +1,46 @@
+//go:build plugin_dns || plugin_dnstcp || plugin_modbus || !plugin_selective
+
+package services
+
+import (
+	"crypto/rand"
+	"encoding/binary"
+	"fmt"
+	"time"
+)
+
+func randomUint16() uint16 {
+	var b [2]byte
+	if _, err := rand.Read(b[:]); err == nil {
+		return binary.BigEndian.Uint16(b[:])
+	}
+	return uint16(time.Now().UnixNano())
+}
+
+func buildDNSRootNSQuery(id uint16) []byte {
+	query := make([]byte, 17)
+	binary.BigEndian.PutUint16(query[0:2], id)
+	binary.BigEndian.PutUint16(query[2:4], 0x0100)
+	binary.BigEndian.PutUint16(query[4:6], 1)
+	query[12] = 0x00
+	binary.BigEndian.PutUint16(query[13:15], 2)
+	binary.BigEndian.PutUint16(query[15:17], 1)
+	return query
+}
+
+func parseDNSResponse(data []byte, id uint16) (string, bool) {
+	if len(data) < 12 || binary.BigEndian.Uint16(data[0:2]) != id {
+		return "", false
+	}
+	flags := binary.BigEndian.Uint16(data[2:4])
+	if flags&0x8000 == 0 {
+		return "", false
+	}
+
+	rcode := flags & 0x000f
+	qd := binary.BigEndian.Uint16(data[4:6])
+	an := binary.BigEndian.Uint16(data[6:8])
+	ns := binary.BigEndian.Uint16(data[8:10])
+	ar := binary.BigEndian.Uint16(data[10:12])
+	return fmt.Sprintf("DNS response rcode=%d qd=%d an=%d ns=%d ar=%d", rcode, qd, an, ns, ar), true
+}