Payloads: add NotValidBefore transaction attribute

Fixes neo-project#1992.

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

@@ -0,0 +1,46 @@
+using Neo.IO;
+using Neo.Json;
+using Neo.Persistence;
+using Neo.SmartContract.Native;
+using System.IO;
+
+namespace Neo.Network.P2P.Payloads
+{
+    public class NotValidBefore : TransactionAttribute
+    {
+        /// <summary>
+        /// Indicates that the transaction is not valid before this height.
+        /// </summary>
+        public uint Height;
+
+        public override TransactionAttributeType Type => TransactionAttributeType.NotValidBefore;
+
+        public override bool AllowMultiple => false;
+
+        public override int Size => base.Size +
+            sizeof(uint); // Height.
+
+        protected override void DeserializeWithoutType(ref MemoryReader reader)
+        {
+            Height = reader.ReadUInt32();
+        }
+
+        protected override void SerializeWithoutType(BinaryWriter writer)
+        {
+            writer.Write(Height);
+        }
+
+        public override JObject ToJson()
+        {
+            JObject json = base.ToJson();
+            json["height"] = Height;
+            return json;
+        }
+
+        public override bool Verify(DataCache snapshot, Transaction tx)
+        {
+            var block_height = NativeContract.Ledger.CurrentIndex(snapshot);
+            return block_height >= Height;
+        }
+    }
+}

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

@@ -27,6 +27,12 @@ public enum TransactionAttributeType : byte
         /// Indicates that the transaction is an oracle response.
         /// </summary>
         [ReflectionCache(typeof(OracleResponse))]
-        OracleResponse = 0x11
+        OracleResponse = 0x11,
+
+        /// <summary>
+        /// Indicates that the transaction is not valid before <see cref="NotValidBefore.Height"/>.
+        /// </summary>
+        [ReflectionCache(typeof(NotValidBefore))]
+        NotValidBefore = 0x20
     }
 }

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

@@ -0,0 +1,75 @@
+using FluentAssertions;
+using Microsoft.VisualStudio.TestTools.UnitTesting;
+using Neo.IO;
+using Neo.Network.P2P.Payloads;
+using Neo.SmartContract.Native;
+using System;
+
+namespace Neo.UnitTests.Network.P2P.Payloads
+{
+    [TestClass]
+    public class UT_NotValidBefore
+    {
+        [TestMethod]
+        public void Size_Get()
+        {
+            var test = new NotValidBefore();
+            test.Size.Should().Be(5);
+        }
+
+        [TestMethod]
+        public void ToJson()
+        {
+            var test = new NotValidBefore();
+            test.Height = 42;
+            var json = test.ToJson().ToString();
+            Assert.AreEqual(@"{""type"":""NotValidBefore"",""height"":42}", json);
+        }
+
+        [TestMethod]
+        public void DeserializeAndSerialize()
+        {
+            var test = new NotValidBefore();
+
+            var clone = test.ToArray().AsSerializable<NotValidBefore>();
+            Assert.AreEqual(clone.Type, test.Type);
+
+            // As transactionAttribute
+
+            byte[] buffer = test.ToArray();
+            var reader = new MemoryReader(buffer);
+            clone = TransactionAttribute.DeserializeFrom(ref reader) as NotValidBefore;
+            Assert.AreEqual(clone.Type, test.Type);
+
+            // Wrong type
+
+            buffer[0] = 0xff;
+            reader = new MemoryReader(buffer);
+            try
+            {
+                TransactionAttribute.DeserializeFrom(ref reader);
+                Assert.Fail();
+            }
+            catch (FormatException) { }
+            reader = new MemoryReader(buffer);
+            try
+            {
+                new NotValidBefore().Deserialize(ref reader);
+                Assert.Fail();
+            }
+            catch (FormatException) { }
+        }
+
+        [TestMethod]
+        public void Verify()
+        {
+            var test = new NotValidBefore();
+            var snapshot = TestBlockchain.GetTestSnapshot();
+            test.Height = NativeContract.Ledger.CurrentIndex(snapshot) + 1;
+
+            Assert.IsFalse(test.Verify(snapshot, new Transaction()));
+            test.Height--;
+            Assert.IsTrue(test.Verify(snapshot, new Transaction()));
+        }
+    }
+}