Refuel (#2444)

src/neo/SmartContract/ApplicationEngine.cs

@@ -40,7 +40,7 @@ public partial class ApplicationEngine : ExecutionEngine
 
         private static IApplicationEngineProvider applicationEngineProvider;
         private static Dictionary<uint, InteropDescriptor> services;
-        private readonly long gas_amount;
+        private long gas_amount;
         private List<NotifyEventArgs> notifications;
         private List<IDisposable> disposables;
         private readonly Dictionary<UInt160, int> invocationCounter = new();
@@ -147,6 +147,14 @@ protected internal void AddGas(long gas)
                 throw new InvalidOperationException("Insufficient GAS.");
         }
 
+        internal void Refuel(long gas)
+        {
+            checked
+            {
+                gas_amount += gas;
+            }
+        }
+
         protected override void OnFault(Exception ex)
         {
             FaultException = ex;

src/neo/SmartContract/Native/GasToken.cs

@@ -1,5 +1,8 @@
+#pragma warning disable IDE0051
+
 using Neo.Cryptography.ECC;
 using Neo.Network.P2P.Payloads;
+using System;
 
 namespace Neo.SmartContract.Native
 {
@@ -33,5 +36,14 @@ internal override async ContractTask OnPersist(ApplicationEngine engine)
             UInt160 primary = Contract.CreateSignatureRedeemScript(validators[engine.PersistingBlock.PrimaryIndex]).ToScriptHash();
             await Mint(engine, primary, totalNetworkFee, false);
         }
+
+        [ContractMethod(CpuFee = 1 << 15, RequiredCallFlags = CallFlags.States | CallFlags.AllowNotify)]
+        private async ContractTask Refuel(ApplicationEngine engine, UInt160 account, long amount)
+        {
+            if (amount < 0) throw new ArgumentOutOfRangeException(nameof(amount));
+            if (!engine.CheckWitnessInternal(account)) throw new InvalidOperationException();
+            await Burn(engine, account, amount);
+            engine.Refuel(amount);
+        }
     }
 }

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

@@ -6,6 +6,7 @@
 using Neo.SmartContract;
 using Neo.SmartContract.Native;
 using Neo.UnitTests.Extensions;
+using Neo.VM;
 using System;
 using System.Linq;
 using System.Numerics;
@@ -35,6 +36,67 @@ public void TestSetup()
         [TestMethod]
         public void Check_Decimals() => NativeContract.GAS.Decimals(_snapshot).Should().Be(8);
 
+        [TestMethod]
+        public void Refuel()
+        {
+            // Prepare
+
+            var wallet = TestUtils.GenerateTestWallet();
+            var snapshot = TestBlockchain.GetTestSnapshot();
+
+            using var unlock = wallet.Unlock("");
+            var accBalance = wallet.CreateAccount();
+            var accNoBalance = wallet.CreateAccount();
+
+            // Fake balance
+
+            var key = NativeContract.GAS.CreateStorageKey(20, accNoBalance.ScriptHash);
+            var entry = snapshot.GetAndChange(key, () => new StorageItem(new AccountState()));
+            entry.GetInteroperable<AccountState>().Balance = 1 * NativeContract.GAS.Factor;
+
+            key = NativeContract.GAS.CreateStorageKey(20, accBalance.ScriptHash);
+            entry = snapshot.GetAndChange(key, () => new StorageItem(new AccountState()));
+            entry.GetInteroperable<AccountState>().Balance = 100 * NativeContract.GAS.Factor;
+
+            snapshot.Commit();
+
+            // Make transaction
+
+            byte[] script;
+            using (ScriptBuilder sb = new())
+            {
+                sb.EmitDynamicCall(NativeContract.GAS.Hash, "refuel", accBalance.ScriptHash, 100 * NativeContract.GAS.Factor);
+                sb.Emit(OpCode.DROP);
+                sb.EmitSysCall(ApplicationEngine.System_Runtime_GasLeft);
+                script = sb.ToArray();
+            }
+
+            var signers = new Signer[]{ new Signer
+                {
+                    Account = accBalance.ScriptHash,
+                    Scopes =  WitnessScope.CalledByEntry
+                } ,
+                new Signer
+                {
+                    Account = accNoBalance.ScriptHash,
+                    Scopes =  WitnessScope.CalledByEntry
+                } };
+
+            var tx = wallet.MakeTransaction(snapshot, script, accBalance.ScriptHash, signers);
+            Assert.IsNotNull(tx);
+
+            // Check
+
+            using ApplicationEngine engine = ApplicationEngine.Create(TriggerType.Application, tx, snapshot, settings: TestBlockchain.TheNeoSystem.Settings, gas: tx.NetworkFee);
+            engine.LoadScript(tx.Script);
+            Assert.AreEqual(VMState.HALT, engine.Execute());
+            Assert.AreEqual(1, engine.ResultStack.Count);
+            Assert.AreEqual(100_00300140, engine.ResultStack.Pop().GetInteger());
+
+            entry = snapshot.GetAndChange(key, () => new StorageItem(new AccountState()));
+            Assert.AreEqual(0, entry.GetInteroperable<AccountState>().Balance);
+        }
+
         [TestMethod]
         public async Task Check_BalanceOfTransferAndBurn()
         {