Merge pull request #784 from nspcc-dev/neo3/null

vm: support NULL stack item

pkg/smartcontract/param_type.go

@@ -30,6 +30,7 @@ const (
 	ArrayType            ParamType = 0x10
 	MapType              ParamType = 0x12
 	InteropInterfaceType ParamType = 0xf0
+	AnyType              ParamType = 0xfe
 	VoidType             ParamType = 0xff
 )
 
@@ -60,6 +61,8 @@ func (pt ParamType) String() string {
 		return "InteropInterface"
 	case VoidType:
 		return "Void"
+	case AnyType:
+		return "Any"
 	default:
 		return ""
 	}
@@ -154,6 +157,8 @@ func ParseParamType(typ string) (ParamType, error) {
 		return InteropInterfaceType, nil
 	case "void":
 		return VoidType, nil
+	case "any":
+		return AnyType, nil
 	default:
 		return UnknownType, errors.Errorf("Unknown contract parameter type: %s", typ)
 	}

pkg/vm/opcode/opcode.go

@@ -89,6 +89,7 @@ const (
 	PUSHDATA2   Opcode = 0x4D
 	PUSHDATA4   Opcode = 0x4E
 	PUSHM1      Opcode = 0x4F
+	PUSHNULL    Opcode = 0x50
 	PUSH1       Opcode = 0x51
 	PUSHT       Opcode = PUSH1
 	PUSH2       Opcode = 0x52
@@ -118,6 +119,8 @@ const (
 	SYSCALL  Opcode = 0x68
 	TAILCALL Opcode = 0x69
 
+	ISNULL Opcode = 0x70
+
 	// Stack
 	DUPFROMALTSTACK Opcode = 0x6A
 	TOALTSTACK      Opcode = 0x6B

pkg/vm/stack_item.go

@@ -185,6 +185,44 @@ func (i *StructItem) Clone() *StructItem {
 	return ret
 }
 
+// NullItem represents null on the stack.
+type NullItem struct{}
+
+// String implements StackItem interface.
+func (i NullItem) String() string {
+	return "Null"
+}
+
+// Value implements StackItem interface.
+func (i NullItem) Value() interface{} {
+	return nil
+}
+
+// Dup implements StackItem interface.
+// There is no need to perform a real copy here,
+// as NullItem has no internal state.
+func (i NullItem) Dup() StackItem {
+	return i
+}
+
+// TryBytes implements StackItem interface.
+func (i NullItem) TryBytes() ([]byte, error) {
+	return nil, errors.New("can't convert Null to ByteArray")
+}
+
+// Equals implements StackItem interface.
+func (i NullItem) Equals(s StackItem) bool {
+	_, ok := s.(NullItem)
+	return ok
+}
+
+// ToContractParameter implements StackItem interface.
+func (i NullItem) ToContractParameter(map[StackItem]bool) smartcontract.Parameter {
+	return smartcontract.Parameter{
+		Type: smartcontract.AnyType,
+	}
+}
+
 // BigIntegerItem represents a big integer on the stack.
 type BigIntegerItem struct {
 	value *big.Int

pkg/vm/vm.go

@@ -560,6 +560,13 @@ func (v *VM) execute(ctx *Context, op opcode.Opcode, parameter []byte) (err erro
 	case opcode.PUSHDATA1, opcode.PUSHDATA2, opcode.PUSHDATA4:
 		v.estack.PushVal(parameter)
 
+	case opcode.PUSHNULL:
+		v.estack.PushVal(NullItem{})
+
+	case opcode.ISNULL:
+		res := v.estack.Pop().value.Equals(NullItem{})
+		v.estack.PushVal(res)
+
 	// Stack operations.
 	case opcode.TOALTSTACK:
 		v.astack.Push(v.estack.Pop())

pkg/vm/vm_test.go

@@ -197,6 +197,31 @@ func TestStackLimitPUSH1Bad(t *testing.T) {
 	checkVMFailed(t, v)
 }
 
+func TestPUSHNULL(t *testing.T) {
+	prog := makeProgram(opcode.PUSHNULL, opcode.PUSHNULL, opcode.EQUAL)
+	v := load(prog)
+	require.NoError(t, v.Step())
+	require.Equal(t, 1, v.estack.Len())
+	runVM(t, v)
+	require.True(t, v.estack.Pop().Bool())
+}
+
+func TestISNULL(t *testing.T) {
+	t.Run("Integer", func(t *testing.T) {
+		prog := makeProgram(opcode.PUSH1, opcode.ISNULL)
+		v := load(prog)
+		runVM(t, v)
+		require.False(t, v.estack.Pop().Bool())
+	})
+
+	t.Run("Null", func(t *testing.T) {
+		prog := makeProgram(opcode.PUSHNULL, opcode.ISNULL)
+		v := load(prog)
+		runVM(t, v)
+		require.True(t, v.estack.Pop().Bool())
+	})
+}
+
 // appendBigStruct returns a program which:
 // 1. pushes size Structs on stack
 // 2. packs them into a new struct