From fe66c0ff8aadb2d62f782f16db893aa255d00cfd Mon Sep 17 00:00:00 2001
From: Shargon <shargon@gmail.com>
Date: Thu, 26 Mar 2020 06:13:29 +0100
Subject: [PATCH] Add GasLeft syscall (#1509)

---
 src/neo/SmartContract/ApplicationEngine.cs    |  1 +
 .../SmartContract/InteropService.Runtime.cs   |  7 +++
 .../SmartContract/UT_Syscalls.cs              | 51 +++++++++++++++++++
 3 files changed, 59 insertions(+)

diff --git a/src/neo/SmartContract/ApplicationEngine.cs b/src/neo/SmartContract/ApplicationEngine.cs
index 500e75a6b5..fda6a3ba84 100644
--- a/src/neo/SmartContract/ApplicationEngine.cs
+++ b/src/neo/SmartContract/ApplicationEngine.cs
@@ -25,6 +25,7 @@ public partial class ApplicationEngine : ExecutionEngine
         public IVerifiable ScriptContainer { get; }
         public StoreView Snapshot { get; }
         public long GasConsumed { get; private set; } = 0;
+        public long GasLeft => testMode ? -1 : gas_amount - GasConsumed;
 
         public UInt160 CurrentScriptHash => CurrentContext?.GetState<ExecutionContextState>().ScriptHash;
         public UInt160 CallingScriptHash => CurrentContext?.GetState<ExecutionContextState>().CallingScriptHash;
diff --git a/src/neo/SmartContract/InteropService.Runtime.cs b/src/neo/SmartContract/InteropService.Runtime.cs
index b1c0dec22e..2e1eb8083d 100644
--- a/src/neo/SmartContract/InteropService.Runtime.cs
+++ b/src/neo/SmartContract/InteropService.Runtime.cs
@@ -29,6 +29,7 @@ public static class Runtime
             public static readonly InteropDescriptor Log = Register("System.Runtime.Log", Runtime_Log, 0_01000000, TriggerType.All, CallFlags.AllowNotify);
             public static readonly InteropDescriptor Notify = Register("System.Runtime.Notify", Runtime_Notify, 0_01000000, TriggerType.All, CallFlags.AllowNotify);
             public static readonly InteropDescriptor GetNotifications = Register("System.Runtime.GetNotifications", Runtime_GetNotifications, 0_00010000, TriggerType.All, CallFlags.None);
+            public static readonly InteropDescriptor GasLeft = Register("System.Runtime.GasLeft", Runtime_GasLeft, 0_00000400, TriggerType.All, CallFlags.None);
 
             private static bool CheckItemForNotification(StackItem state)
             {
@@ -167,6 +168,12 @@ private static bool Runtime_CheckWitness(ApplicationEngine engine)
                 return true;
             }
 
+            private static bool Runtime_GasLeft(ApplicationEngine engine)
+            {
+                engine.Push(engine.GasLeft);
+                return true;
+            }
+
             private static bool Runtime_GetInvocationCounter(ApplicationEngine engine)
             {
                 if (!engine.InvocationCounter.TryGetValue(engine.CurrentScriptHash, out var counter))
diff --git a/tests/neo.UnitTests/SmartContract/UT_Syscalls.cs b/tests/neo.UnitTests/SmartContract/UT_Syscalls.cs
index 8044d8ae95..442450f844 100644
--- a/tests/neo.UnitTests/SmartContract/UT_Syscalls.cs
+++ b/tests/neo.UnitTests/SmartContract/UT_Syscalls.cs
@@ -266,6 +266,57 @@ public void System_ExecutionEngine_GetScriptContainer()
             }
         }
 
+        [TestMethod]
+        public void System_Runtime_GasLeft()
+        {
+            var snapshot = Blockchain.Singleton.GetSnapshot();
+
+            using (var script = new ScriptBuilder())
+            {
+                script.Emit(OpCode.NOP);
+                script.EmitSysCall(InteropService.Runtime.GasLeft);
+                script.Emit(OpCode.NOP);
+                script.EmitSysCall(InteropService.Runtime.GasLeft);
+                script.Emit(OpCode.NOP);
+                script.Emit(OpCode.NOP);
+                script.Emit(OpCode.NOP);
+                script.EmitSysCall(InteropService.Runtime.GasLeft);
+
+                // Execute
+
+                var engine = new ApplicationEngine(TriggerType.Application, null, snapshot, 100_000_000, false);
+                engine.LoadScript(script.ToArray());
+                Assert.AreEqual(engine.Execute(), VMState.HALT);
+
+                // Check the results
+
+                CollectionAssert.AreEqual
+                    (
+                    engine.ResultStack.Select(u => (int)((VM.Types.Integer)u).GetBigInteger()).ToArray(),
+                    new int[] { 99_999_570, 99_999_140, 99_998_650 }
+                    );
+            }
+
+            // Check test mode
+
+            using (var script = new ScriptBuilder())
+            {
+                script.EmitSysCall(InteropService.Runtime.GasLeft);
+
+                // Execute
+
+                var engine = new ApplicationEngine(TriggerType.Application, null, snapshot, 0, true);
+                engine.LoadScript(script.ToArray());
+
+                // Check the results
+
+                Assert.AreEqual(engine.Execute(), VMState.HALT);
+                Assert.AreEqual(1, engine.ResultStack.Count);
+                Assert.IsInstanceOfType(engine.ResultStack.Peek(), typeof(Integer));
+                Assert.AreEqual(-1, engine.ResultStack.Pop().GetBigInteger());
+            }
+        }
+
         [TestMethod]
         public void System_Runtime_GetInvocationCounter()
         {