Implement NEP-17

src/neo/SmartContract/ApplicationEngine.Contract.cs

@@ -18,6 +18,7 @@ partial class ApplicationEngine
         public static readonly InteropDescriptor System_Contract_Create = Register("System.Contract.Create", nameof(CreateContract), 0, CallFlags.AllowModifyStates, false);
         public static readonly InteropDescriptor System_Contract_Update = Register("System.Contract.Update", nameof(UpdateContract), 0, CallFlags.AllowModifyStates, false);
         public static readonly InteropDescriptor System_Contract_Destroy = Register("System.Contract.Destroy", nameof(DestroyContract), 0_01000000, CallFlags.AllowModifyStates, false);
+        public static readonly InteropDescriptor System_Contract_Exists = Register("System.Contract.Exists", nameof(ContractExists), 0_01000000, CallFlags.AllowCall, false);
         public static readonly InteropDescriptor System_Contract_Call = Register("System.Contract.Call", nameof(CallContract), 0_01000000, CallFlags.AllowCall, false);
         public static readonly InteropDescriptor System_Contract_CallEx = Register("System.Contract.CallEx", nameof(CallContractEx), 0_01000000, CallFlags.AllowCall, false);
         public static readonly InteropDescriptor System_Contract_IsStandard = Register("System.Contract.IsStandard", nameof(IsStandardContract), 0_00030000, CallFlags.AllowStates, true);
@@ -118,6 +119,16 @@ protected internal void DestroyContract()
                     Snapshot.Storages.Delete(key);
         }
 
+        internal bool ContractExists(UInt160 contractHash, string method)
+        {
+            if (contractHash is null) return false;
+
+            ContractState contract = Snapshot.Contracts.TryGet(contractHash);
+            if (contract is null) return false;
+
+            return method == null || contract.Manifest.Abi.GetMethod(method) != null;
+        }
+
         protected internal void CallContract(UInt160 contractHash, string method, Array args)
         {
             CallContractInternal(contractHash, method, args, CallFlags.All);
@@ -130,7 +141,7 @@ protected internal void CallContractEx(UInt160 contractHash, string method, Arra
             CallContractInternal(contractHash, method, args, callFlags);
         }
 
-        private void CallContractInternal(UInt160 contractHash, string method, Array args, CallFlags flags)
+        protected internal void CallContractInternal(UInt160 contractHash, string method, Array args, CallFlags flags, CheckReturnType returnType = CheckReturnType.EnsureNotEmpty)
         {
             if (method.StartsWith('_')) throw new ArgumentException($"Invalid Method Name: {method}");
 
@@ -143,7 +154,7 @@ private void CallContractInternal(UInt160 contractHash, string method, Array arg
             if (currentManifest != null && !currentManifest.CanCall(contract.Manifest, method))
                 throw new InvalidOperationException($"Cannot Call Method {method} Of Contract {contractHash} From Contract {CurrentScriptHash}");
 
-            CallContractInternal(contract, md, args, flags, CheckReturnType.EnsureNotEmpty);
+            CallContractInternal(contract, md, args, flags, returnType);
         }
 
         private void CallContractInternal(ContractState contract, ContractMethodDescriptor method, Array args, CallFlags flags, CheckReturnType checkReturnValue)

src/neo/SmartContract/ApplicationEngine.cs

@@ -18,11 +18,12 @@ namespace Neo.SmartContract
 {
     public partial class ApplicationEngine : ExecutionEngine
     {
-        private enum CheckReturnType : byte
+        protected internal enum CheckReturnType : byte
         {
             None = 0,
             EnsureIsEmpty = 1,
-            EnsureNotEmpty = 2
+            EnsureNotEmpty = 2,
+            DropResult = 3
         }
 
         private class InvocationState
@@ -120,6 +121,13 @@ protected override void ContextUnloaded(ExecutionContext context)
                             throw new InvalidOperationException();
                         break;
                     }
+                case CheckReturnType.DropResult:
+                    {
+                        if (context.EvaluationStack.Count == 1)
+                            context.EvaluationStack.Pop();
+                        else throw new InvalidOperationException();
+                        break;
+                    }
             }
             switch (state.Callback)
             {

src/neo/SmartContract/Native/Tokens/Nep5Token.cs

@@ -68,7 +68,21 @@ internal protected virtual void Mint(ApplicationEngine engine, UInt160 account,
             state.Balance += amount;
             storage = engine.Snapshot.Storages.GetAndChange(CreateStorageKey(Prefix_TotalSupply), () => new StorageItem(BigInteger.Zero));
             storage.Add(amount);
-            engine.SendNotification(Hash, "Transfer", new Array { StackItem.Null, account.ToArray(), amount });
+            onPostTransfer(engine, null, account, amount);
+        }
+
+        private void onPostTransfer(ApplicationEngine engine, UInt160 from, UInt160 to, BigInteger amount)
+        {
+            // Send notification
+
+            engine.SendNotification(Hash, "Transfer",
+                new Array { from == null ? StackItem.Null : from.ToArray(), to == null ? StackItem.Null : to.ToArray(), amount });
+
+            if (!engine.ContractExists(to, "onPayment")) return;
+
+            // Call onPayment method if exists
+
+            engine.CallContractInternal(to, "onPayment", new Array(engine.ReferenceCounter) { amount }, CallFlags.All, ApplicationEngine.CheckReturnType.DropResult);
         }
 
         internal protected virtual void Burn(ApplicationEngine engine, UInt160 account, BigInteger amount)
@@ -86,7 +100,7 @@ internal protected virtual void Burn(ApplicationEngine engine, UInt160 account,
                 state.Balance -= amount;
             storage = engine.Snapshot.Storages.GetAndChange(CreateStorageKey(Prefix_TotalSupply));
             storage.Add(-amount);
-            engine.SendNotification(Hash, "Transfer", new Array { account.ToArray(), StackItem.Null, amount });
+            onPostTransfer(engine, account, null, amount);
         }
 
         [ContractMethod(0_01000000, CallFlags.AllowStates)]
@@ -105,7 +119,7 @@ public virtual BigInteger BalanceOf(StoreView snapshot, UInt160 account)
             return storage.GetInteroperable<TState>().Balance;
         }
 
-        [ContractMethod(0_08000000, CallFlags.AllowModifyStates)]
+        [ContractMethod(0_09000000, CallFlags.AllowModifyStates)]
         protected virtual bool Transfer(ApplicationEngine engine, UInt160 from, UInt160 to, BigInteger amount)
         {
             if (amount.Sign < 0) throw new ArgumentOutOfRangeException(nameof(amount));
@@ -146,7 +160,7 @@ protected virtual bool Transfer(ApplicationEngine engine, UInt160 from, UInt160
                     state_to.Balance += amount;
                 }
             }
-            engine.SendNotification(Hash, "Transfer", new Array { from.ToArray(), to.ToArray(), amount });
+            onPostTransfer(engine, from, to, amount);
             return true;
         }