Publish default values for null static arrays

src/ZB.MOM.WW.LmxOpcUa.Host/OpcUa/LmxNodeManager.cs

@@ -27,10 +27,18 @@ namespace ZB.MOM.WW.LmxOpcUa.Host.OpcUa
         // Ref-counted MXAccess subscriptions
         private readonly Dictionary<string, int> _subscriptionRefCounts = new Dictionary<string, int>(StringComparer.OrdinalIgnoreCase);
         private readonly Dictionary<string, BaseDataVariableState> _tagToVariableNode = new Dictionary<string, BaseDataVariableState>(StringComparer.OrdinalIgnoreCase);
+        private readonly Dictionary<string, TagMetadata> _tagMetadata = new Dictionary<string, TagMetadata>(StringComparer.OrdinalIgnoreCase);
 
         private readonly object _lock = new object();
         private IDictionary<NodeId, IList<IReference>>? _externalReferences;
 
+        private sealed class TagMetadata
+        {
+            public int MxDataType { get; set; }
+            public bool IsArray { get; set; }
+            public int? ArrayDimension { get; set; }
+        }
+
         /// <summary>
         /// Gets the mapping from OPC UA node identifiers to the Galaxy tag references used for runtime I/O.
         /// </summary>
@@ -91,6 +99,7 @@ namespace ZB.MOM.WW.LmxOpcUa.Host.OpcUa
             {
                 _nodeIdToTagReference.Clear();
                 _tagToVariableNode.Clear();
+                _tagMetadata.Clear();
                 VariableNodeCount = 0;
                 ObjectNodeCount = 0;
 
@@ -198,6 +207,7 @@ namespace ZB.MOM.WW.LmxOpcUa.Host.OpcUa
                 PredefinedNodes.Clear();
                 _nodeIdToTagReference.Clear();
                 _tagToVariableNode.Clear();
+                _tagMetadata.Clear();
                 _subscriptionRefCounts.Clear();
 
                 // Rebuild
@@ -266,12 +276,19 @@ namespace ZB.MOM.WW.LmxOpcUa.Host.OpcUa
 
             variable.AccessLevel = AccessLevels.CurrentReadOrWrite;
             variable.UserAccessLevel = AccessLevels.CurrentReadOrWrite;
+            variable.Value = NormalizePublishedValue(attr.FullTagReference, null);
             variable.StatusCode = StatusCodes.BadWaitingForInitialData;
             variable.Timestamp = DateTime.UtcNow;
 
             AddPredefinedNode(SystemContext, variable);
             _nodeIdToTagReference[nodeIdString] = attr.FullTagReference;
             _tagToVariableNode[attr.FullTagReference] = variable;
+            _tagMetadata[attr.FullTagReference] = new TagMetadata
+            {
+                MxDataType = attr.MxDataType,
+                IsArray = attr.IsArray,
+                ArrayDimension = attr.ArrayDimension
+            };
             VariableNodeCount++;
         }
 
@@ -372,7 +389,7 @@ namespace ZB.MOM.WW.LmxOpcUa.Host.OpcUa
                     try
                     {
                         var vtq = _mxAccessClient.ReadAsync(tagRef).GetAwaiter().GetResult();
-                        results[i] = DataValueConverter.FromVtq(vtq);
+                        results[i] = CreatePublishedDataValue(tagRef, vtq);
                         errors[i] = ServiceResult.Good;
                     }
                     catch (Exception ex)
@@ -446,7 +463,7 @@ namespace ZB.MOM.WW.LmxOpcUa.Host.OpcUa
             if (!int.TryParse(indexRange, out var index) || index < 0)
                 return false;
 
-            var currentValue = _mxAccessClient.ReadAsync(tagRef).GetAwaiter().GetResult().Value;
+            var currentValue = NormalizePublishedValue(tagRef, _mxAccessClient.ReadAsync(tagRef).GetAwaiter().GetResult().Value);
             if (currentValue is not Array currentArray || currentArray.Rank != 1 || index >= currentArray.Length)
                 return false;
 
@@ -491,13 +508,47 @@ namespace ZB.MOM.WW.LmxOpcUa.Host.OpcUa
             if (!_tagToVariableNode.TryGetValue(tagRef, out var variable))
                 return;
 
-            var dataValue = DataValueConverter.FromVtq(Vtq.Good(value));
+            var dataValue = CreatePublishedDataValue(tagRef, Vtq.Good(value));
             variable.Value = dataValue.Value;
             variable.StatusCode = dataValue.StatusCode;
             variable.Timestamp = dataValue.SourceTimestamp;
             variable.ClearChangeMasks(SystemContext, false);
         }
 
+        private DataValue CreatePublishedDataValue(string tagRef, Vtq vtq)
+        {
+            var normalizedValue = NormalizePublishedValue(tagRef, vtq.Value);
+            if (ReferenceEquals(normalizedValue, vtq.Value))
+                return DataValueConverter.FromVtq(vtq);
+
+            return DataValueConverter.FromVtq(new Vtq(normalizedValue, vtq.Timestamp, vtq.Quality));
+        }
+
+        private object? NormalizePublishedValue(string tagRef, object? value)
+        {
+            if (value != null)
+                return value;
+
+            if (!_tagMetadata.TryGetValue(tagRef, out var metadata) || !metadata.IsArray || !metadata.ArrayDimension.HasValue)
+                return null;
+
+            return CreateDefaultArrayValue(metadata);
+        }
+
+        private static Array CreateDefaultArrayValue(TagMetadata metadata)
+        {
+            var elementType = MxDataTypeMapper.MapToClrType(metadata.MxDataType);
+            var values = Array.CreateInstance(elementType, metadata.ArrayDimension!.Value);
+
+            if (elementType == typeof(string))
+            {
+                for (int i = 0; i < values.Length; i++)
+                    values.SetValue(string.Empty, i);
+            }
+
+            return values;
+        }
+
         #endregion
 
         #region Subscription Delivery
@@ -588,7 +639,7 @@ namespace ZB.MOM.WW.LmxOpcUa.Host.OpcUa
             {
                 try
                 {
-                    var dataValue = DataValueConverter.FromVtq(vtq);
+                    var dataValue = CreatePublishedDataValue(address, vtq);
                     variable.Value = dataValue.Value;
                     variable.StatusCode = dataValue.StatusCode;
                     variable.Timestamp = dataValue.SourceTimestamp;

tests/ZB.MOM.WW.LmxOpcUa.Tests/Integration/ArrayWriteTests.cs

@@ -90,6 +90,37 @@ namespace ZB.MOM.WW.LmxOpcUa.Tests.Integration
             }
         }
 
+        /// <summary>
+        /// Confirms that a null runtime value for a statically sized array is exposed as a typed fixed-length array.
+        /// </summary>
+        [Fact]
+        public async Task Read_NullStaticArray_ReturnsDefaultTypedArray()
+        {
+            var fixture = OpcUaServerFixture.WithFakeMxAccessClient();
+            fixture.MxAccessClient!.TagValues["MESReceiver_001.MoveInPartNumbers[]"] = Vtq.Good(null);
+
+            await fixture.InitializeAsync();
+            try
+            {
+                using var client = new OpcUaTestClient();
+                await client.ConnectAsync(fixture.EndpointUrl);
+
+                var nodeId = client.MakeNodeId("MESReceiver_001.MoveInPartNumbers");
+
+                var value = client.Read(nodeId).Value as string[];
+                value.ShouldNotBeNull();
+                value.Length.ShouldBe(50);
+                value.ShouldAllBe(v => v == string.Empty);
+
+                var dimensions = client.ReadAttribute(nodeId, Attributes.ArrayDimensions).Value as uint[];
+                dimensions.ShouldBe(new uint[] { 50 });
+            }
+            finally
+            {
+                await fixture.DisposeAsync();
+            }
+        }
+
         /// <summary>
         /// Confirms that an indexed write also updates the published OPC UA value seen by subscribed clients.
         /// </summary>
@@ -136,5 +167,37 @@ namespace ZB.MOM.WW.LmxOpcUa.Tests.Integration
                 await fixture.DisposeAsync();
             }
         }
+
+        /// <summary>
+        /// Confirms that indexed writes succeed even when the current runtime array value is null.
+        /// </summary>
+        [Fact]
+        public async Task Write_SingleArrayElement_WhenCurrentArrayIsNull_UsesDefaultArray()
+        {
+            var fixture = OpcUaServerFixture.WithFakeMxAccessClient();
+            fixture.MxAccessClient!.TagValues["MESReceiver_001.MoveInPartNumbers[]"] = Vtq.Good(null);
+
+            await fixture.InitializeAsync();
+            try
+            {
+                using var client = new OpcUaTestClient();
+                await client.ConnectAsync(fixture.EndpointUrl);
+
+                var nodeId = client.MakeNodeId("MESReceiver_001.MoveInPartNumbers");
+                var status = client.Write(nodeId, new[] { "UPDATED-PART" }, indexRange: "1");
+                StatusCode.IsGood(status).ShouldBe(true);
+
+                var after = client.Read(nodeId).Value as string[];
+                after.ShouldNotBeNull();
+                after.Length.ShouldBe(50);
+                after[0].ShouldBe(string.Empty);
+                after[1].ShouldBe("UPDATED-PART");
+                after[2].ShouldBe(string.Empty);
+            }
+            finally
+            {
+                await fixture.DisposeAsync();
+            }
+        }
     }
 }