Fix GetHashCode for IEnumerable properties (confluentinc#2432)

* Fix GetHashCode for IEnumerable properties

* Minor fix

* Minor fix

Author: rayokota

src/Confluent.SchemaRegistry.Encryption/Rest/DataContracts/Kek.cs

@@ -90,7 +90,7 @@ public override int GetHashCode()
                 var hashCode = (Name != null ? Name.GetHashCode() : 0);
                 hashCode = (hashCode * 397) ^ (KmsType != null ? KmsType.GetHashCode() : 0);
                 hashCode = (hashCode * 397) ^ (KmsKeyId != null ? KmsKeyId.GetHashCode() : 0);
-                hashCode = (hashCode * 397) ^ (KmsProps != null ? KmsProps.GetHashCode() : 0);
+                hashCode = (hashCode * 397) ^ Utils.IEnumerableHashCode(KmsProps);
                 hashCode = (hashCode * 397) ^ (Doc != null ? Doc.GetHashCode() : 0);
                 hashCode = (hashCode * 397) ^ Shared.GetHashCode();
                 hashCode = (hashCode * 397) ^ Deleted.GetHashCode();

src/Confluent.SchemaRegistry.Encryption/Rest/DataContracts/UpdateKek.cs

@@ -60,7 +60,7 @@ public override int GetHashCode()
         {
             unchecked
             {
-                var hashCode = (KmsProps != null ? KmsProps.GetHashCode() : 0);
+                var hashCode = Utils.IEnumerableHashCode(KmsProps);
                 hashCode = (hashCode * 397) ^ (Doc != null ? Doc.GetHashCode() : 0);
                 hashCode = (hashCode * 397) ^ Shared.GetHashCode();
                 return hashCode;

src/Confluent.SchemaRegistry/Rest/DataContracts/Metadata.cs

@@ -66,9 +66,9 @@ public override int GetHashCode()
         {
             unchecked
             {
-                var hashCode = (Tags != null ? Tags.GetHashCode() : 0);
-                hashCode = (hashCode * 397) ^ (Properties != null ? Properties.GetHashCode() : 0);
-                hashCode = (hashCode * 397) ^ (Sensitive != null ? Sensitive.GetHashCode() : 0);
+                var hashCode = Utils.IEnumerableHashCode(Tags);
+                hashCode = (hashCode * 397) ^ Utils.IEnumerableHashCode(Properties);
+                hashCode = (hashCode * 397) ^ Utils.IEnumerableHashCode(Sensitive);
                 return hashCode;
             }
         }

src/Confluent.SchemaRegistry/Rest/DataContracts/Rule.cs

@@ -116,8 +116,8 @@ public override int GetHashCode()
                 hashCode = (hashCode * 397) ^ (int)Kind;
                 hashCode = (hashCode * 397) ^ (int)Mode;
                 hashCode = (hashCode * 397) ^ (Type != null ? Type.GetHashCode() : 0);
-                hashCode = (hashCode * 397) ^ (Tags != null ? Tags.GetHashCode() : 0);
-                hashCode = (hashCode * 397) ^ (Params != null ? Params.GetHashCode() : 0);
+                hashCode = (hashCode * 397) ^ Utils.IEnumerableHashCode(Tags);
+                hashCode = (hashCode * 397) ^ Utils.IEnumerableHashCode(Params);
                 hashCode = (hashCode * 397) ^ (Expr != null ? Expr.GetHashCode() : 0);
                 hashCode = (hashCode * 397) ^ (OnSuccess != null ? OnSuccess.GetHashCode() : 0);
                 hashCode = (hashCode * 397) ^ (OnFailure != null ? OnFailure.GetHashCode() : 0);

src/Confluent.SchemaRegistry/Rest/DataContracts/RuleSet.cs

@@ -77,8 +77,8 @@ public override int GetHashCode()
       {
         unchecked
         {
-          return ((MigrationRules != null ? MigrationRules.GetHashCode() : 0) * 397) ^ 
-                 (DomainRules != null ? DomainRules.GetHashCode() : 0);
+          return (Utils.IEnumerableHashCode(MigrationRules) * 397) ^
+                 Utils.IEnumerableHashCode(DomainRules);
         }
       }
     }

src/Confluent.SchemaRegistry/Rest/DataContracts/Schema.cs

@@ -271,38 +271,13 @@ public override int GetHashCode()
             unchecked
             {
                 var hashCode = SchemaString.GetHashCode();
-                hashCode = (hashCode * 397) ^ (References != null ? GetListHashCode(References) : 0); 
+                hashCode = (hashCode * 397) ^ Utils.IEnumerableHashCode(References);
                 hashCode = (hashCode * 397) ^ (Metadata != null ? Metadata.GetHashCode() : 0);
                 hashCode = (hashCode * 397) ^ (RuleSet != null ? RuleSet.GetHashCode() : 0);
                 return hashCode;
             }
         }
 
-        /// <summary>
-        ///     Returns a hash code for a list of objects.
-        /// </summary>
-        /// <param name="list">
-        ///     The list to get the hash code for.
-        /// </param> 
-        /// <returns>
-        ///     An integer that specifies a hash value for this instance.
-        /// </returns>
-        private int GetListHashCode<T>(IList<T> list)
-        {
-            if (list == null || list.Count == 0)
-                return 0;
-
-            unchecked
-            {
-                int hash = 0;
-                foreach (var item in list)
-                {
-                    hash += item?.GetHashCode() ?? 0;
-                }
-                return hash;
-            }
-        }
-
         /// <summary>
         ///     Compares this instance with another instance of this object type and indicates whether
         ///     this instance precedes, follows, or appears in the same position in the sort order

src/Confluent.SchemaRegistry/Utils.cs

@@ -14,11 +14,8 @@
 //
 // Refer to LICENSE for more information.
 
-using System;
-using System.Collections;
 using System.Collections.Generic;
 using System.Linq;
-using Confluent.Kafka;
 
 #if NET8_0_OR_GREATER
 using System.Buffers.Text;
@@ -74,6 +71,23 @@ public static bool ListEquals<T>(IList<T> a, IList<T> b)
             return a.SequenceEqual(b);
         }
 
+        public static int IEnumerableHashCode<T>(IEnumerable<T> items)
+        {
+            if (items == null) return 0;
+
+            var hash = 0;
+
+            using (var enumerator = items.GetEnumerator())
+            {
+                while (enumerator.MoveNext())
+                {
+                    hash = (hash * 397) ^ (enumerator.Current?.GetHashCode() ?? 0);
+                }
+            }
+
+            return hash;
+        }
+
         internal static bool IsBase64String(string value)
         {
 #if NET8_0_OR_GREATER