Add native protocol service plugins

plugins/services/modbus_test.go

@@ -0,0 +1,22 @@
+//go:build plugin_modbus || !plugin_selective
+
+package services
+
+import (
+	"encoding/binary"
+	"strings"
+	"testing"
+)
+
+func TestModbusDeviceIDRequestAndResponse(t *testing.T) {
+	req := buildModbusDeviceIDRequest(0x1001)
+	if len(req) != 11 || binary.BigEndian.Uint16(req[0:2]) != 0x1001 || req[7] != 0x2b {
+		t.Fatalf("unexpected modbus request: %#v", req)
+	}
+
+	header := []byte{0x10, 0x01, 0x00, 0x00, 0x00, 0x03, 0xff}
+	banner, ok := parseModbusResponse(header, []byte{0x2b, 0x0e}, 0x1001)
+	if !ok || !strings.Contains(banner, "Modbus TCP") {
+		t.Fatalf("unexpected modbus banner: %q ok=%v", banner, ok)
+	}
+}