Implement NotaryAssisted transaction attribute

src/Neo.CLI/CLI/MainService.Blockchain.cs

@@ -212,6 +212,10 @@ public void OnShowTransactionCommand(UInt256 hash)
                                 ConsoleHelper.Info("", "    Type: ", $"{n.Type}");
                                 ConsoleHelper.Info("", "  Height: ", $"{n.Height}");
                                 break;
+                            case NotaryAssisted n:
+                                ConsoleHelper.Info("", "    Type: ", $"{n.Type}");
+                                ConsoleHelper.Info("", "   NKeys: ", $"{n.NKeys}");
+                                break;
                             default:
                                 ConsoleHelper.Info("", "  Type: ", $"{attribute.Type}");
                                 ConsoleHelper.Info("", "  Size: ", $"{attribute.Size} Byte(s)");

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

@@ -0,0 +1,76 @@
+// Copyright (C) 2015-2024 The Neo Project.
+//
+// NotaryAssisted.cs file belongs to the neo project and is free
+// software distributed under the MIT software license, see the
+// accompanying file LICENSE in the main directory of the
+// repository 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 Neo.IO;
+using Neo.Json;
+using Neo.Persistence;
+using Neo.SmartContract.Native;
+using System.IO;
+using System.Linq;
+
+namespace Neo.Network.P2P.Payloads
+{
+    public class NotaryAssisted : TransactionAttribute
+    {
+        /// <summary>
+        /// Native Notary contract hash stub used until native Notary contract is properly implemented.
+        /// </summary>
+        private static readonly UInt160 notaryHash = UInt160.Parse("0xc1e14f19c3e60d0b9244d06dd7ba9b113135ec3b");
+
+        /// <summary>
+        /// Indicates the number of keys participating in the transaction (main or fallback) signing process.
+        /// </summary>
+        public byte NKeys;
+
+        public override TransactionAttributeType Type => TransactionAttributeType.NotaryAssisted;
+
+        public override bool AllowMultiple => false;
+
+        public override int Size => base.Size + sizeof(byte);
+
+        protected override void DeserializeWithoutType(ref MemoryReader reader)
+        {
+            NKeys = reader.ReadByte();
+        }
+
+        protected override void SerializeWithoutType(BinaryWriter writer)
+        {
+            writer.Write(NKeys);
+        }
+
+        public override JObject ToJson()
+        {
+            JObject json = base.ToJson();
+            json["nkeys"] = NKeys;
+            return json;
+        }
+
+        public override bool Verify(DataCache snapshot, Transaction tx)
+        {
+            return tx.Signers.Any(p => p.Account.Equals(notaryHash));
+        }
+
+        /// <summary>
+        /// Calculates the network fee needed to pay for NotaryAssisted attribute. According to the
+        /// https://github.com/neo-project/neo/issues/1573#issuecomment-704874472, network fee consists of
+        /// the base Notary service fee per key multiplied by the expected number of transactions that should
+        /// be collected by the service to complete Notary request increased by one (for Notary node witness
+        /// itself).
+        /// </summary>
+        /// <param name="snapshot">The snapshot used to read data.</param>
+        /// <param name="tx">The transaction to calculate.</param>
+        /// <returns>The network fee of the NotaryAssisted attribute.</returns>
+        public override long CalculateNetworkFee(DataCache snapshot, Transaction tx)
+        {
+            return (NKeys + 1) * base.CalculateNetworkFee(snapshot, tx);
+        }
+    }
+}

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

@@ -40,6 +40,12 @@ public enum TransactionAttributeType : byte
         /// Indicates that the transaction conflicts with <see cref="Conflicts.Hash"/>.
         /// </summary>
         [ReflectionCache(typeof(Conflicts))]
-        Conflicts = 0x21
+        Conflicts = 0x21,
+
+        /// <summary>
+        /// Indicates that the transaction uses notary request service with <see cref="NotaryAssisted.NKeys" number of keys/>.
+        /// </summary>
+        [ReflectionCache(typeof(NotaryAssisted))]
+        NotaryAssisted = 0x22
     }
 }

src/Neo/SmartContract/Native/GasToken.cs

@@ -43,6 +43,14 @@ internal override async ContractTask OnPersist(ApplicationEngine engine)
             {
                 await Burn(engine, tx.Sender, tx.SystemFee + tx.NetworkFee);
                 totalNetworkFee += tx.NetworkFee;
+
+                // Reward for NotaryAssisted attribute will be minted to designated notary nodes
+                // by Notary contract.
+                var notaryAssisted = tx.GetAttribute<NotaryAssisted>();
+                if (notaryAssisted is not null)
+                {
+                    totalNetworkFee -= (notaryAssisted.NKeys + 1) * Policy.GetAttributeFee(engine.Snapshot, (byte)notaryAssisted.Type);
+                }
             }
             ECPoint[] validators = NEO.GetNextBlockValidators(engine.Snapshot, engine.ProtocolSettings.ValidatorsCount);
             UInt160 primary = Contract.CreateSignatureRedeemScript(validators[engine.PersistingBlock.PrimaryIndex]).ToScriptHash();

src/Neo/SmartContract/Native/PolicyContract.cs

@@ -43,6 +43,11 @@ public sealed class PolicyContract : NativeContract
         /// </summary>
         public const uint DefaultAttributeFee = 0;
 
+        /// <summary>
+        /// The default fee for NotaryAssisted attribute.
+        /// </summary>
+        public const uint DefaultNotaryAssistedAttributeFee = 1000_0000;
+
         /// <summary>
         /// The maximum execution fee factor that the committee can set.
         /// </summary>
@@ -73,6 +78,7 @@ internal override ContractTask Initialize(ApplicationEngine engine, Hardfork? ha
                 engine.Snapshot.Add(CreateStorageKey(Prefix_FeePerByte), new StorageItem(DefaultFeePerByte));
                 engine.Snapshot.Add(CreateStorageKey(Prefix_ExecFeeFactor), new StorageItem(DefaultExecFeeFactor));
                 engine.Snapshot.Add(CreateStorageKey(Prefix_StoragePrice), new StorageItem(DefaultStoragePrice));
+                engine.Snapshot.Add(CreateStorageKey(Prefix_AttributeFee).Add((byte)TransactionAttributeType.NotaryAssisted), new StorageItem(DefaultNotaryAssistedAttributeFee));
             }
             return ContractTask.CompletedTask;
         }

tests/Neo.UnitTests/Network/P2P/Payloads/UT_NotaryAssisted.cs

@@ -0,0 +1,90 @@
+// Copyright (C) 2015-2024 The Neo Project.
+//
+// UT_NotaryAssisted.cs file belongs to the neo project and is free
+// software distributed under the MIT software license, see the
+// accompanying file LICENSE in the main directory of the
+// repository 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 FluentAssertions;
+using Microsoft.VisualStudio.TestTools.UnitTesting;
+using Neo.IO;
+using Neo.Network.P2P.Payloads;
+using Neo.SmartContract;
+using Neo.SmartContract.Native;
+using Neo.VM;
+using System;
+
+namespace Neo.UnitTests.Network.P2P.Payloads
+{
+    [TestClass]
+    public class UT_NotaryAssisted
+    {
+        private static readonly UInt160 notaryHash = UInt160.Parse("0xc1e14f19c3e60d0b9244d06dd7ba9b113135ec3b");
+
+        [TestMethod]
+        public void Size_Get()
+        {
+            var attr = new NotaryAssisted() { NKeys = 4 };
+            attr.Size.Should().Be(1 + 1);
+        }
+
+        [TestMethod]
+        public void ToJson()
+        {
+            var attr = new NotaryAssisted() { NKeys = 4 };
+            var json = attr.ToJson().ToString();
+            Assert.AreEqual(@"{""type"":""NotaryAssisted"",""nkeys"":4}", json);
+        }
+
+        [TestMethod]
+        public void DeserializeAndSerialize()
+        {
+            var attr = new NotaryAssisted() { NKeys = 4 };
+
+            var clone = attr.ToArray().AsSerializable<NotaryAssisted>();
+            Assert.AreEqual(clone.Type, attr.Type);
+
+            // As transactionAttribute
+            byte[] buffer = attr.ToArray();
+            var reader = new MemoryReader(buffer);
+            clone = TransactionAttribute.DeserializeFrom(ref reader) as NotaryAssisted;
+            Assert.AreEqual(clone.Type, attr.Type);
+
+            // Wrong type
+            buffer[0] = 0xff;
+            Assert.ThrowsException<FormatException>(() =>
+            {
+                var reader = new MemoryReader(buffer);
+                TransactionAttribute.DeserializeFrom(ref reader);
+            });
+        }
+
+        [TestMethod]
+        public void Verify()
+        {
+            var attr = new NotaryAssisted() { NKeys = 4 };
+
+            // Temporary use Notary contract hash stub for valid transaction.
+            var txGood = new Transaction { Signers = new Signer[] { new Signer() { Account = notaryHash } } };
+            var txBad = new Transaction { Signers = new Signer[] { new Signer() { Account = UInt160.Parse("0xa400ff00ff00ff00ff00ff00ff00ff00ff00ff01") } } };
+            var snapshot = TestBlockchain.GetTestSnapshot();
+
+            Assert.IsTrue(attr.Verify(snapshot, txGood));
+            Assert.IsFalse(attr.Verify(snapshot, txBad));
+        }
+
+        [TestMethod]
+        public void CalculateNetworkFee()
+        {
+            var snapshot = TestBlockchain.GetTestSnapshot();
+            var attr = new NotaryAssisted() { NKeys = 4 };
+            var tx = new Transaction { Signers = new Signer[] { new Signer() { Account = notaryHash } } };
+
+            Assert.AreEqual((4 + 1) * 1000_0000, attr.CalculateNetworkFee(snapshot, tx));
+        }
+    }
+}

tests/Neo.UnitTests/SmartContract/Native/UT_GasToken.cs

@@ -10,17 +10,35 @@
 // modifications are permitted.
 
 using FluentAssertions;
+using FluentAssertions;
+using Microsoft.VisualStudio.TestTools.UnitTesting;
 using Microsoft.VisualStudio.TestTools.UnitTesting;
+using Neo.Cryptography.ECC;
+using Neo.IO;
 using Neo.IO;
 using Neo.Network.P2P.Payloads;
+using Neo.Network.P2P.Payloads;
+using Neo.Persistence;
 using Neo.Persistence;
 using Neo.SmartContract;
+using Neo.SmartContract;
+using Neo.SmartContract.Native;
 using Neo.SmartContract.Native;
 using Neo.UnitTests.Extensions;
+using Neo.UnitTests.Extensions;
+using Neo.VM;
+using Neo.Wallets;
+using System;
+using System;
 using System;
 using System.Linq;
+using System.Linq;
+using System.Numerics;
+using System.Numerics;
 using System.Numerics;
 using System.Threading.Tasks;
+using VMTypes = Neo.VM.Types;
+// using VMArray = Neo.VM.Types.Array;
 
 namespace Neo.UnitTests.SmartContract.Native
 {
@@ -151,5 +169,61 @@ internal static StorageKey CreateStorageKey(byte prefix, byte[] key = null)
                 Key = buffer
             };
         }
+
+        [TestMethod]
+        public void Check_OnPersist_NotaryAssisted()
+        {
+            // Hardcode test values.
+            const uint defaultNotaryssestedFeePerKey = 1000_0000;
+            const byte NKeys1 = 4;
+            const byte NKeys2 = 6;
+
+            // Generate two transactions with NotaryAssisted attributes with hardcoded NKeys values.
+            var from = Contract.GetBFTAddress(TestProtocolSettings.Default.StandbyValidators);
+            var tx1 = TestUtils.GetTransaction(from);
+            tx1.Attributes = new TransactionAttribute[] { new NotaryAssisted() { NKeys = NKeys1 } };
+            var netFee1 = 1_0000_0000;
+            tx1.NetworkFee = netFee1;
+            var tx2 = TestUtils.GetTransaction(from);
+            tx2.Attributes = new TransactionAttribute[] { new NotaryAssisted() { NKeys = NKeys2 } };
+            var netFee2 = 2_0000_0000;
+            tx2.NetworkFee = netFee2;
+
+            // Calculate expected Notary nodes reward.
+            var expectedNotaryReward = (NKeys1 + 1) * defaultNotaryssestedFeePerKey + (NKeys2 + 1) * defaultNotaryssestedFeePerKey;
+
+            // Build block to check transaction fee distribution during Gas OnPersist.
+            var persistingBlock = new Block
+            {
+                Header = new Header
+                {
+                    Index = (uint)TestProtocolSettings.Default.CommitteeMembersCount,
+                    MerkleRoot = UInt256.Zero,
+                    NextConsensus = UInt160.Zero,
+                    PrevHash = UInt256.Zero,
+                    Witness = new Witness() { InvocationScript = Array.Empty<byte>(), VerificationScript = Array.Empty<byte>() }
+                },
+                Transactions = new Transaction[] { tx1, tx2 }
+            };
+            var snapshot = _snapshot.CreateSnapshot();
+            var script = new ScriptBuilder();
+            script.EmitSysCall(ApplicationEngine.System_Contract_NativeOnPersist);
+            var engine = ApplicationEngine.Create(TriggerType.OnPersist, null, snapshot, persistingBlock, settings: TestBlockchain.TheNeoSystem.Settings);
+
+            // Check that block's Primary balance is 0.
+            ECPoint[] validators = NativeContract.NEO.GetNextBlockValidators(engine.Snapshot, engine.ProtocolSettings.ValidatorsCount);
+            var primary = Contract.CreateSignatureRedeemScript(validators[engine.PersistingBlock.PrimaryIndex]).ToScriptHash();
+            NativeContract.GAS.BalanceOf(engine.Snapshot, primary).Should().Be(0);
+
+            // Execute OnPersist script.
+            engine.LoadScript(script.ToArray());
+            Assert.IsTrue(engine.Execute() == VMState.HALT);
+
+            // Check that proper amount of GAS was minted to block's Primary and the rest
+            // will be minted to Notary nodes as a reward once Notary contract is implemented.
+            Assert.AreEqual(2 + 1, engine.Notifications.Count()); // burn tx1 and tx2 network fee + mint primary reward
+            Assert.AreEqual(netFee1 + netFee2 - expectedNotaryReward, engine.Notifications[2].State[2]);
+            NativeContract.GAS.BalanceOf(engine.Snapshot, primary).Should().Be(netFee1 + netFee2 - expectedNotaryReward);
+        }
     }
 }