Add reserved attribute

src/Neo/Network/P2P/Payloads/ReservedAttribute.cs

@@ -0,0 +1,45 @@
+// Copyright (C) 2015-2023 The Neo Project.
+// 
+// The neo is free software distributed under the MIT software license, 
+// see the accompanying file LICENSE in the main directory of the
+// project or http://www.opensource.org/licenses/mit-license.php 
+// for more details.
+// 
+// Redistribution and use in source and binary forms with or without
+// modifications are permitted.
+
+using System;
+using System.IO;
+using Neo.IO;
+using Neo.Json;
+
+namespace Neo.Network.P2P.Payloads
+{
+    /// <summary>
+    /// Reserved attribute for dApps.
+    /// </summary>
+    public class ReservedAttribute : TransactionAttribute
+    {
+        private byte[] _reserved;
+
+        public override bool AllowMultiple => true;
+        public override TransactionAttributeType Type => TransactionAttributeType.ReservedAttribute;
+
+        protected override void DeserializeWithoutType(ref MemoryReader reader)
+        {
+            _reserved = reader.ReadVarMemory(ushort.MaxValue).ToArray();
+        }
+
+        protected override void SerializeWithoutType(BinaryWriter writer)
+        {
+            writer.WriteVarBytes(_reserved);
+        }
+
+        public override JObject ToJson()
+        {
+            var json = base.ToJson();
+            json["value"] = Convert.ToBase64String(_reserved);
+            return json;
+        }
+    }
+}

src/Neo/Network/P2P/Payloads/TransactionAttributeType.cs

@@ -33,6 +33,12 @@ public enum TransactionAttributeType : byte
         /// Indicates that the transaction is not valid before <see cref="NotValidBefore.Height"/>.
         /// </summary>
         [ReflectionCache(typeof(NotValidBefore))]
-        NotValidBefore = 0x20
+        NotValidBefore = 0x20,
+
+        /// <summary>
+        /// Indicates that the transaction is a reserved attribute.
+        /// </summary>
+        [ReflectionCache(typeof(ReservedAttribute))]
+        ReservedAttribute = 0xf0
     }
 }