Allow to define a custom StringComparsion for Equals Operator (#3048)

* Add string comparison enhancements to ContentFilter.

- Introduce static `EqualsOperatorDefaultStringComparison` Property in the `ContentFilter` class for customizable string comparison.
- Update `IsEqual` method in the `Utils` class to accept an optional `StringComparison` parameter.

* Add Test

* fix default stringComparsion Operator to be Ordinal

* Remove obsolete DBNull check

* Add Comment

Author: romanett

Stack/Opc.Ua.Core/Stack/Types/ContentFilter.Evaluate.cs

@@ -24,6 +24,14 @@ namespace Opc.Ua
     /// </summary>
     public partial class ContentFilter
     {
+        #region  Public Static Properties
+        /// <summary>
+        /// Set the default StringComparison to use when evaluating the Equals operator.
+        /// This property is meant to be set as a config setting and not set / reset on a per context basis, to ensure consistency
+        /// </summary>
+        public static StringComparison EqualsOperatorDefaultStringComparison { get; set; } = StringComparison.Ordinal;
+        #endregion
+
         #region Public functions
         /// <summary>
         /// Evaluates the first element in the ContentFilter. If the first or any 
@@ -407,14 +415,19 @@ private static bool IsEqual(object value1, object value2)
                 return value1 == null && value2 == null;
             }
 
-            if (value1 is DBNull || value2 is DBNull)
+            if (value1.GetType() != value2.GetType())
             {
-                return value1 is DBNull && value2 is DBNull;
+                return false;
             }
 
-            if (value1.GetType() != value2.GetType())
+            //check for strings
+            if (value1 is string string1)
             {
-                return false;
+                if (value2 is not string string2)
+                {
+                    return false;
+                }
+                return string1.Equals(string2, EqualsOperatorDefaultStringComparison);
             }
 
             return Utils.IsEqual(value1, value2);

Stack/Opc.Ua.Core/Types/Utils/Utils.cs

@@ -2631,7 +2631,7 @@ public static void UpdateExtension<T>(ref XmlElementCollection extensions, XmlQu
                 extensions.Add(document.DocumentElement);
             }
         }
-#endregion
+        #endregion
 
         #region Reflection Helper Functions
         /// <summary>
@@ -2985,7 +2985,7 @@ public static bool ValidateNonce(byte[] nonce, MessageSecurityMode securityMode,
             [Obsolete("Use equivalent method from the Opc.Ua.Nonce class")]
             public static bool ValidateNonce(byte[] nonce, MessageSecurityMode securityMode, uint minNonceLength)
             {
-                return NewNonceImplementation.ValidateNonce(nonce,securityMode, minNonceLength);
+                return NewNonceImplementation.ValidateNonce(nonce, securityMode, minNonceLength);
             }
         }
 
@@ -3248,6 +3248,6 @@ public static bool IsRunningOnMono()
         {
             return s_isRunningOnMonoValue.Value;
         }
-#endregion
+        #endregion
     }
 }

Tests/Opc.Ua.Core.Tests/Types/ContentFilter/ContentFilterTests.cs

@@ -312,6 +312,29 @@ public void NonBoolWithBinary(object operandFirst1, object operandFirst2, Filter
             Assert.AreEqual(expectedResult, result);
         }
 
+        [Test]
+        [TestCase("mainstation", "mainstation", StringComparison.Ordinal, true)]
+        [TestCase("mainstation", "Mainstation", StringComparison.Ordinal, false)]
+        [TestCase("mainstation", "Mainstation", StringComparison.OrdinalIgnoreCase, true)]
+        [TestCase("mainstation", "Mainstation", StringComparison.InvariantCultureIgnoreCase, true)]
+        [TestCase("mainstation", "Mainstation", StringComparison.InvariantCulture, false)]
+        [TestCase("mainstation", "mainstation", StringComparison.InvariantCulture, true)]
+        public void EqualsStringComparsion(string operandFirst1, string operandFirst2, StringComparison stringComparison, object expectedResult)
+        {
+            Opc.Ua.ContentFilter.EqualsOperatorDefaultStringComparison = stringComparison;
+            LiteralOperand loperand1 = new LiteralOperand { Value = new Variant(operandFirst1)};
+            LiteralOperand loperand2 = new LiteralOperand { Value = new Variant(operandFirst2)};
+
+            ContentFilterElement filterElement = new ContentFilterElement();
+            filterElement.FilterOperator = FilterOperator.Equals;
+            filterElement.SetOperands(new List<LiteralOperand>() { loperand1, loperand2 });
+            Filter.WhereClause.Elements = new[] { filterElement };
+
+            // apply filter.
+            object result = Filter.WhereClause.Evaluate(FilterContext, TestFilterTarget);
+            Assert.AreEqual(expectedResult, result);
+        }
+
 
         #endregion
     }