Fix 1244 Mempool.ReverifyTransactions (neo-project#1248)

* add internal to DB and WriteBatch

* reset db.cs writebatch.cs

* fix Nep5Token.Burn method

* format

* format

* reset and fix memorypool.ReverifyTransactions

* reset and fix ReverifyTransactions

* add ut

* remove commit

* fix BlockPersistAndReverificationWillAbandonTxAsBalanceTransfered.balance

* update comments

neo.UnitTests/Ledger/UT_MemoryPool.cs

@@ -8,6 +8,7 @@
 using Neo.Network.P2P.Payloads;
 using Neo.Persistence;
 using Neo.Plugins;
+using Neo.SmartContract;
 using Neo.SmartContract.Native;
 using System;
 using System.Collections;
@@ -92,6 +93,31 @@ private Transaction CreateTransactionWithFee(long fee)
             return mock.Object;
         }
 
+        private Transaction CreateTransactionWithFeeAndBalanceVerify(long fee)
+        {
+            Random random = new Random();
+            var randomBytes = new byte[16];
+            random.NextBytes(randomBytes);
+            Mock<Transaction> mock = new Mock<Transaction>();
+            UInt160 sender = UInt160.Zero;
+            mock.Setup(p => p.Reverify(It.IsAny<Snapshot>(), It.IsAny<BigInteger>())).Returns(((Snapshot snapshot, BigInteger amount) => NativeContract.GAS.BalanceOf(snapshot, sender) >= amount + fee));
+            mock.Setup(p => p.Verify(It.IsAny<Snapshot>(), It.IsAny<BigInteger>())).Returns(true);
+            mock.Object.Script = randomBytes;
+            mock.Object.Sender = sender;
+            mock.Object.NetworkFee = fee;
+            mock.Object.Attributes = new TransactionAttribute[0];
+            mock.Object.Cosigners = new Cosigner[0];
+            mock.Object.Witnesses = new[]
+            {
+                new Witness
+                {
+                    InvocationScript = new byte[0],
+                    VerificationScript = new byte[0]
+                }
+            };
+            return mock.Object;
+        }
+
         private Transaction CreateTransaction(long fee = -1)
         {
             if (fee != -1)
@@ -115,6 +141,17 @@ private void AddTransaction(Transaction txToAdd)
             _unit.TryAdd(txToAdd.Hash, txToAdd);
         }
 
+        private void AddTransactionsWithBalanceVerify(int count, long fee)
+        {
+            for (int i = 0; i < count; i++)
+            {
+                var txToAdd = CreateTransactionWithFeeAndBalanceVerify(fee);
+                _unit.TryAdd(txToAdd.Hash, txToAdd);
+            }
+
+            Console.WriteLine($"created {count} tx");
+        }
+
         [TestMethod]
         public void CapacityTest()
         {
@@ -171,6 +208,38 @@ public void BlockPersistMovesTxToUnverifiedAndReverification()
             _unit.UnverifiedSortedTxCount.Should().Be(0);
         }
 
+        [TestMethod]
+        public void BlockPersistAndReverificationWillAbandonTxAsBalanceTransfered()
+        {
+            long txFee = 1;
+            AddTransactionsWithBalanceVerify(70, txFee);
+
+            _unit.SortedTxCount.Should().Be(70);
+
+            var block = new Block
+            {
+                Transactions = _unit.GetSortedVerifiedTransactions().Take(10).ToArray()
+            };
+
+            // Simulate the transfer process in tx by burning the balance
+            UInt160 sender = block.Transactions[0].Sender;
+            Snapshot snapshot = Blockchain.Singleton.GetSnapshot();
+            BigInteger balance = NativeContract.GAS.BalanceOf(snapshot, sender);
+
+            ApplicationEngine applicationEngine = new ApplicationEngine(TriggerType.All, block, snapshot, (long)balance);
+            NativeContract.GAS.Burn(applicationEngine, sender, balance);
+            NativeContract.GAS.Mint(applicationEngine, sender, txFee * 30); // Set the balance to meet 30 txs only
+
+            // Persist block and reverify all the txs in mempool, but half of the txs will be discarded
+            _unit.UpdatePoolForBlockPersisted(block, snapshot);
+            _unit.SortedTxCount.Should().Be(30);
+            _unit.UnverifiedSortedTxCount.Should().Be(0);
+
+            // Revert the balance
+            NativeContract.GAS.Burn(applicationEngine, sender, txFee * 30);
+            NativeContract.GAS.Mint(applicationEngine, sender, balance);
+        }
+
         private void VerifyTransactionsSortedDescending(IEnumerable<Transaction> transactions)
         {
             Transaction lastTransaction = null;

neo/Ledger/MemoryPool.cs

@@ -417,7 +417,10 @@ private int ReverifyTransactions(SortedSet<PoolItem> verifiedSortedTxPool,
             foreach (PoolItem item in unverifiedSortedTxPool.Reverse().Take(count))
             {
                 if (item.Tx.Reverify(snapshot, SendersFeeMonitor.GetSenderFee(item.Tx.Sender)))
+                {
                     reverifiedItems.Add(item);
+                    SendersFeeMonitor.AddSenderFee(item.Tx);
+                }
                 else // Transaction no longer valid -- it will be removed from unverifiedTxPool.
                     invalidItems.Add(item);
 
@@ -438,7 +441,6 @@ private int ReverifyTransactions(SortedSet<PoolItem> verifiedSortedTxPool,
                 {
                     if (_unsortedTransactions.TryAdd(item.Tx.Hash, item))
                     {
-                        SendersFeeMonitor.AddSenderFee(item.Tx);
                         verifiedSortedTxPool.Add(item);
 
                         if (item.LastBroadcastTimestamp < rebroadcastCutOffTime)
@@ -447,6 +449,8 @@ private int ReverifyTransactions(SortedSet<PoolItem> verifiedSortedTxPool,
                             item.LastBroadcastTimestamp = DateTime.UtcNow;
                         }
                     }
+                    else
+                        SendersFeeMonitor.RemoveSenderFee(item.Tx);
 
                     _unverifiedTransactions.Remove(item.Tx.Hash);
                     unverifiedSortedTxPool.Remove(item);