vm: duplicate an item in Dup

TestDupByteArray and TestDupInt were failing before this patch.

pkg/vm/context.go

@@ -159,6 +159,11 @@ func (c *Context) Value() interface{} {
 	return c
 }
 
+// Dup implements StackItem interface.
+func (c *Context) Dup() StackItem {
+	return c
+}
+
 func (c *Context) atBreakPoint() bool {
 	for _, n := range c.breakPoints {
 		if n == c.ip {

pkg/vm/stack.go

@@ -346,7 +346,7 @@ func (s *Stack) Dup(n int) *Element {
 	}
 
 	return &Element{
-		value: e.value,
+		value: e.value.Dup(),
 	}
 }
 

pkg/vm/stack_item.go

@@ -15,6 +15,8 @@ import (
 type StackItem interface {
 	fmt.Stringer
 	Value() interface{}
+	// Dup duplicates current StackItem.
+	Dup() StackItem
 }
 
 func makeStackItem(v interface{}) StackItem {
@@ -107,6 +109,12 @@ func (i *StructItem) String() string {
 	return "Struct"
 }
 
+// Dup implements StackItem interface.
+func (i *StructItem) Dup() StackItem {
+	// it's a reference type, so no copying here.
+	return i
+}
+
 // Clone returns a Struct with all Struct fields copied by value.
 // Array fields are still copied by reference.
 func (i *StructItem) Clone() *StructItem {
@@ -148,6 +156,12 @@ func (i *BigIntegerItem) String() string {
 	return "BigInteger"
 }
 
+// Dup implements StackItem interface.
+func (i *BigIntegerItem) Dup() StackItem {
+	n := new(big.Int)
+	return &BigIntegerItem{n.Set(i.value)}
+}
+
 // MarshalJSON implements the json.Marshaler interface.
 func (i *BigIntegerItem) MarshalJSON() ([]byte, error) {
 	return json.Marshal(i.value)
@@ -179,6 +193,11 @@ func (i *BoolItem) String() string {
 	return "Bool"
 }
 
+// Dup implements StackItem interface.
+func (i *BoolItem) Dup() StackItem {
+	return &BoolItem{i.value}
+}
+
 // ByteArrayItem represents a byte array on the stack.
 type ByteArrayItem struct {
 	value []byte
@@ -205,6 +224,13 @@ func (i *ByteArrayItem) String() string {
 	return "ByteArray"
 }
 
+// Dup implements StackItem interface.
+func (i *ByteArrayItem) Dup() StackItem {
+	a := make([]byte, len(i.value))
+	copy(a, i.value)
+	return &ByteArrayItem{a}
+}
+
 // ArrayItem represents a new ArrayItem object.
 type ArrayItem struct {
 	value []StackItem
@@ -231,6 +257,12 @@ func (i *ArrayItem) String() string {
 	return "Array"
 }
 
+// Dup implements StackItem interface.
+func (i *ArrayItem) Dup() StackItem {
+	// reference type
+	return i
+}
+
 // MapItem represents Map object.
 type MapItem struct {
 	value map[interface{}]StackItem
@@ -259,6 +291,12 @@ func (i *MapItem) Has(key StackItem) (ok bool) {
 	return
 }
 
+// Dup implements StackItem interface.
+func (i *MapItem) Dup() StackItem {
+	// reference type
+	return i
+}
+
 // Add adds key-value pair to the map.
 func (i *MapItem) Add(key, value StackItem) {
 	i.value[toMapKey(key)] = value
@@ -300,6 +338,12 @@ func (i *InteropItem) String() string {
 	return "InteropItem"
 }
 
+// Dup implements StackItem interface.
+func (i *InteropItem) Dup() StackItem {
+	// reference type
+	return i
+}
+
 // MarshalJSON implements the json.Marshaler interface.
 func (i *InteropItem) MarshalJSON() ([]byte, error) {
 	return json.Marshal(i.value)

pkg/vm/vm_test.go

@@ -2519,6 +2519,42 @@ func TestXSWAPBad2(t *testing.T) {
 	checkVMFailed(t, vm)
 }
 
+func TestDupInt(t *testing.T) {
+	prog := makeProgram(opcode.DUP, opcode.ABS)
+	vm := load(prog)
+	vm.estack.PushVal(-1)
+	runVM(t, vm)
+	assert.Equal(t, 2, vm.estack.Len())
+	assert.Equal(t, int64(1), vm.estack.Pop().BigInt().Int64())
+	assert.Equal(t, int64(-1), vm.estack.Pop().BigInt().Int64())
+}
+
+func TestDupByteArray(t *testing.T) {
+	prog := makeProgram(opcode.PUSHBYTES2, 1, 0,
+		opcode.DUP,
+		opcode.PUSH1,
+		opcode.LEFT,
+		opcode.PUSHBYTES1, 2,
+		opcode.CAT)
+	vm := load(prog)
+	runVM(t, vm)
+	assert.Equal(t, 2, vm.estack.Len())
+	assert.Equal(t, []byte{0x01, 0x02}, vm.estack.Pop().Bytes())
+	assert.Equal(t, []byte{0x01, 0x00}, vm.estack.Pop().Bytes())
+}
+
+func TestDupBool(t *testing.T) {
+	prog := makeProgram(opcode.PUSH0, opcode.NOT,
+		opcode.DUP,
+		opcode.PUSH1, opcode.NOT,
+		opcode.BOOLAND)
+	vm := load(prog)
+	runVM(t, vm)
+	assert.Equal(t, 2, vm.estack.Len())
+	assert.Equal(t, false, vm.estack.Pop().Bool())
+	assert.Equal(t, true, vm.estack.Pop().Bool())
+}
+
 func makeProgram(opcodes ...opcode.Opcode) []byte {
 	prog := make([]byte, len(opcodes)+1) // RET
 	for i := 0; i < len(opcodes); i++ {