From bada93d634a08e0cb639fa00de6c620ddc1ab777 Mon Sep 17 00:00:00 2001
From: Frank Schroeder <frank.schroeder@gmail.com>
Date: Mon, 9 Dec 2024 13:49:06 +0100
Subject: [PATCH] Issue #722: Set DataValue.Value to Variant(nil) for no value

This patch ensures that DataValue.Value contains a Variant(nil) if there
is no value.

Closes #722
---
 ua/datatypes.go      |  2 +-
 ua/datatypes_test.go | 45 ++++++++++++++++++++++++++++++++++++++++++--
 2 files changed, 44 insertions(+), 3 deletions(-)

diff --git a/ua/datatypes.go b/ua/datatypes.go
index c298841c..47117c00 100644
--- a/ua/datatypes.go
+++ b/ua/datatypes.go
@@ -39,8 +39,8 @@ type DataValue struct {
 func (d *DataValue) Decode(b []byte) (int, error) {
 	buf := NewBuffer(b)
 	d.EncodingMask = buf.ReadByte()
+	d.Value = new(Variant)
 	if d.Has(DataValueValue) {
-		d.Value = new(Variant)
 		buf.ReadStruct(d.Value)
 	}
 	if d.Has(DataValueStatusCode) {
diff --git a/ua/datatypes_test.go b/ua/datatypes_test.go
index 937bb1bf..180a59ea 100644
--- a/ua/datatypes_test.go
+++ b/ua/datatypes_test.go
@@ -11,6 +11,17 @@ import (
 
 func TestDataValue(t *testing.T) {
 	cases := []CodecTestCase{
+		{
+			Name: "no value",
+			Struct: &DataValue{
+				EncodingMask: 0x00,
+				Value:        MustVariant(nil),
+			},
+			Bytes: []byte{
+				// EncodingMask
+				0x00,
+			},
+		},
 		{
 			Name: "value only",
 			Struct: &DataValue{
@@ -45,6 +56,23 @@ func TestDataValue(t *testing.T) {
 				0x80, 0x3b, 0xe8, 0xb3, 0x92, 0x4e, 0xd4, 0x01,
 			},
 		},
+		{
+			Name: "source timestamp, server timestamp",
+			Struct: &DataValue{
+				EncodingMask:    0x0c,
+				Value:           MustVariant(nil),
+				SourceTimestamp: time.Date(2018, time.September, 17, 14, 28, 29, 112000000, time.UTC),
+				ServerTimestamp: time.Date(2018, time.September, 17, 14, 28, 29, 112000000, time.UTC),
+			},
+			Bytes: []byte{
+				// EncodingMask
+				0x0c,
+				// SourceTimestamp
+				0x80, 0x3b, 0xe8, 0xb3, 0x92, 0x4e, 0xd4, 0x01,
+				// SeverTimestamp
+				0x80, 0x3b, 0xe8, 0xb3, 0x92, 0x4e, 0xd4, 0x01,
+			},
+		},
 	}
 	RunCodecTest(t, cases)
 }
@@ -52,7 +80,7 @@ func TestDataValue(t *testing.T) {
 func TestDataValueArray(t *testing.T) {
 	cases := []CodecTestCase{
 		{
-			Name: "value only and value, source timestamp, server timestamp",
+			Name: "value only; value, source timestamp, server timestamp; source timestamp, server timestamp",
 			Struct: []*DataValue{
 				{
 					EncodingMask: 0x01,
@@ -64,10 +92,16 @@ func TestDataValueArray(t *testing.T) {
 					SourceTimestamp: time.Date(2018, time.September, 17, 14, 28, 29, 112000000, time.UTC),
 					ServerTimestamp: time.Date(2018, time.September, 17, 14, 28, 29, 112000000, time.UTC),
 				},
+				{
+					EncodingMask:    0x0c,
+					Value:           MustVariant(nil),
+					SourceTimestamp: time.Date(2018, time.September, 17, 14, 28, 29, 112000000, time.UTC),
+					ServerTimestamp: time.Date(2018, time.September, 17, 14, 28, 29, 112000000, time.UTC),
+				},
 			},
 			Bytes: []byte{
 				// length
-				0x02, 0x00, 0x00, 0x00,
+				0x03, 0x00, 0x00, 0x00,
 
 				// EncodingMask
 				0x01,
@@ -84,6 +118,13 @@ func TestDataValueArray(t *testing.T) {
 				0x80, 0x3b, 0xe8, 0xb3, 0x92, 0x4e, 0xd4, 0x01,
 				// ServerTimestamp
 				0x80, 0x3b, 0xe8, 0xb3, 0x92, 0x4e, 0xd4, 0x01,
+
+				// EncodingMask
+				0x0c,
+				// SourceTimestamp
+				0x80, 0x3b, 0xe8, 0xb3, 0x92, 0x4e, 0xd4, 0x01,
+				// ServerTimestamp
+				0x80, 0x3b, 0xe8, 0xb3, 0x92, 0x4e, 0xd4, 0x01,
 			},
 		},
 	}