XmlDecoder/XmlParser: throw BadDecodingError for empty/non-element enumerated arrays

Stack/Opc.Ua.Types/Encoders/XmlDecoder.cs

@@ -1998,10 +1998,15 @@ public ArrayOf<EnumValue> ReadEnumeratedArray(string fieldName)
             {
                 var enums = new List<EnumValue>();
 
-                // TODO: We need to blindly discover the structure of the enumeration array
-                // We peek the first element and push the namespace, then move to it. But
-                // what if there is no first element?  We need test coverage here.
                 XmlQualifiedName xmlName = Peek(XmlNodeType.Element);
+                if (xmlName is null)
+                {
+                    throw ServiceResultException.Create(
+                        StatusCodes.BadDecodingError,
+                        "Unable to read field {0} in function {1}: The enumerated array does not contain any elements.",
+                        fieldName,
+                        nameof(ReadEnumeratedArray));
+                }
                 PushNamespace(xmlName.Namespace);
 
                 while (MoveToElement(xmlName.Name))

Stack/Opc.Ua.Types/Encoders/XmlParser.cs

@@ -2004,9 +2004,15 @@ public ArrayOf<EnumValue> ReadEnumeratedArray(string fieldName)
             {
                 var enums = new List<EnumValue>();
 
-                // TODO: We need to blindly discover the structure of the enumeration array
-                // We peek the first element and push the namespace, then move to it. But
-                // what if there is no first element?  We need test coverage here.
+                if (!MoveToElement(null))
+                {
+                    throw ServiceResultException.Create(
+                        StatusCodes.BadDecodingError,
+                        "Unable to read field {0} in function {1}: The enumerated array does not contain any elements.",
+                        fieldName,
+                        nameof(ReadEnumeratedArray));
+                }
+
                 XmlQualifiedName xmlName = Peek(XmlNodeType.Element);
                 PushNamespace(xmlName.Namespace);
 
@@ -2025,6 +2031,16 @@ public ArrayOf<EnumValue> ReadEnumeratedArray(string fieldName)
                 EndField(fieldName);
                 return enums.ToArrayOf();
             }
+
+            if (LastFieldWasEmpty)
+            {
+                throw ServiceResultException.Create(
+                    StatusCodes.BadDecodingError,
+                    "Unable to read field {0} in function {1}: The enumerated array does not contain any elements.",
+                    fieldName,
+                    nameof(ReadEnumeratedArray));
+            }
+
             return isNil ? default : [];
         }
 

Tests/Opc.Ua.Types.Tests/Encoders/XmlDecoderTests.cs

@@ -2140,6 +2140,28 @@ public void ReadEnumeratedArrayThrowsWhenMaxArrayLengthExceeded()
             Assert.That(ex.StatusCode, Is.EqualTo(StatusCodes.BadEncodingLimitsExceeded));
         }
 
+        [Test]
+        public void ReadEnumeratedArrayThrowsWhenNoElementsPresent()
+        {
+            // Arrange
+            ServiceMessageContext messageContext = CreateMockContext();
+            const string xml = """
+            <ListOfTestEnum xmlns="http://opcfoundation.org/UA/2008/02/Types.xsd">
+                <![CDATA[]]>
+            </ListOfTestEnum>
+            """;
+            using var reader = XmlReader.Create(new StringReader(xml));
+            using var decoder = new XmlDecoder(reader, messageContext);
+            decoder.PushNamespace(Namespaces.OpcUaXsd);
+
+            // Act
+            ServiceResultException ex = Assert.Throws<ServiceResultException>(
+                () => decoder.ReadEnumeratedArray("ListOfTestEnum"));
+
+            // Assert
+            Assert.That(ex.StatusCode, Is.EqualTo(StatusCodes.BadDecodingError));
+        }
+
         [Test]
         public void DecodeMessageReturnsDecodedValue()
         {

Tests/Opc.Ua.Types.Tests/Encoders/XmlParserTests.cs

@@ -1498,6 +1498,7 @@ public void ReadEnumeratedThrowsWhenInvalid()
 
             // Assert
             Assert.That(ex.StatusCode, Is.EqualTo(StatusCodes.BadDecodingError));
+            Assert.That(ex.Message, Does.Contain("does not contain any elements"));
         }
 
         [Test]
@@ -1544,6 +1545,125 @@ public void ReadEnumeratedArrayThrowsWhenMaxArrayLengthExceeded()
             Assert.That(ex.StatusCode, Is.EqualTo(StatusCodes.BadEncodingLimitsExceeded));
         }
 
+        [Test]
+        public void ReadEnumeratedArrayThrowsBadDecodingErrorWhenNoElementsPresent()
+        {
+            // Arrange
+            ServiceMessageContext messageContext = CreateMockContext();
+            const string xml = """
+            <ListOfTestEnum xmlns="http://opcfoundation.org/UA/2008/02/Types.xsd">
+                <![CDATA[]]>
+            </ListOfTestEnum>
+            """;
+            using var decoder = new XmlParser(xml, messageContext);
+            decoder.PushNamespace(Namespaces.OpcUaXsd);
+
+            // Act
+            ServiceResultException ex = Assert.Throws<ServiceResultException>(
+                () => decoder.ReadEnumeratedArray("ListOfTestEnum"));
+
+            // Assert
+            Assert.That(ex.StatusCode, Is.EqualTo(StatusCodes.BadDecodingError));
+            Assert.That(ex.Message, Does.Contain("does not contain any elements"));
+        }
+
+        [Test]
+        public void ReadEnumeratedArrayShouldThrowBadDecodingErrorWhenEmptyContent()
+        {
+            // Arrange
+            ServiceMessageContext messageContext = CreateMockContext();
+            const string xml = """
+            <ListOfTestEnum xmlns="http://opcfoundation.org/UA/2008/02/Types.xsd"></ListOfTestEnum>
+            """;
+            using var decoder = new XmlParser(xml, messageContext);
+            decoder.PushNamespace(Namespaces.OpcUaXsd);
+
+            // Act
+            ServiceResultException ex = Assert.Throws<ServiceResultException>(
+                () => decoder.ReadEnumeratedArray("ListOfTestEnum"));
+
+            // Assert
+            Assert.That(ex.StatusCode, Is.EqualTo(StatusCodes.BadDecodingError));
+            Assert.That(ex.Message, Does.Contain("does not contain any elements"));
+        }
+
+        [Test]
+        public void ReadEnumeratedArrayShouldThrowBadDecodingErrorWhenElementContainsOnlyText()
+        {
+            // Arrange
+            ServiceMessageContext messageContext = CreateMockContext();
+            const string xml = """
+            <ListOfTestEnum xmlns="http://opcfoundation.org/UA/2008/02/Types.xsd">invalid text</ListOfTestEnum>
+            """;
+            using var decoder = new XmlParser(xml, messageContext);
+            decoder.PushNamespace(Namespaces.OpcUaXsd);
+
+            // Act
+            ServiceResultException ex = Assert.Throws<ServiceResultException>(
+                () => decoder.ReadEnumeratedArray("ListOfTestEnum"));
+
+            // Assert
+            Assert.That(ex.StatusCode, Is.EqualTo(StatusCodes.BadDecodingError));
+            Assert.That(ex.Message, Does.Contain("does not contain any elements"));
+        }
+
+        [Test]
+        public void ReadEnumeratedArrayReturnsDefaultWhenNil()
+        {
+            // Arrange
+            ServiceMessageContext messageContext = CreateMockContext();
+            const string xml = """
+            <ListOfTestEnum xmlns="http://opcfoundation.org/UA/2008/02/Types.xsd" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:nil="true" />
+            """;
+            using var decoder = new XmlParser(xml, messageContext);
+            decoder.PushNamespace(Namespaces.OpcUaXsd);
+
+            // Act
+            ArrayOf<EnumValue> result = decoder.ReadEnumeratedArray("ListOfTestEnum");
+
+            // Assert
+            Assert.That(result.IsNull, Is.True);
+        }
+
+        [Test]
+        public void ReadEnumeratedArrayReturnsDefaultWhenMissing()
+        {
+            // Arrange
+            ServiceMessageContext messageContext = CreateMockContext();
+            const string xml = """
+            <Other xmlns="http://opcfoundation.org/UA/2008/02/Types.xsd" />
+            """;
+            using var decoder = new XmlParser(xml, messageContext);
+            decoder.PushNamespace(Namespaces.OpcUaXsd);
+
+            // Act
+            ArrayOf<EnumValue> result = decoder.ReadEnumeratedArray("ListOfTestEnum");
+
+            // Assert
+            Assert.That(result.IsNull, Is.True);
+        }
+
+        [Test]
+        public void ReadEnumeratedArrayShouldReturnCorrectCountForPopulatedArray()
+        {
+            // Arrange
+            ServiceMessageContext messageContext = CreateMockContext();
+            const string xml = """
+            <ListOfTestEnum xmlns="http://opcfoundation.org/UA/2008/02/Types.xsd">
+                <TestEnum>Value1</TestEnum>
+                <TestEnum>Value2</TestEnum>
+            </ListOfTestEnum>
+            """;
+            using var decoder = new XmlParser(xml, messageContext);
+            decoder.PushNamespace(Namespaces.OpcUaXsd);
+
+            // Act
+            ArrayOf<EnumValue> result = decoder.ReadEnumeratedArray("ListOfTestEnum");
+
+            // Assert
+            Assert.That(result.Count, Is.EqualTo(2));
+        }
+
         [Test]
         public void DecodeMessageReturnsDecodedValue()
         {