neo-go/pkg/vm/stack.go

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package vm
import (
"encoding/json"
"errors"
"fmt"
"math/big"
"github.com/nspcc-dev/neo-go/pkg/vm/stackitem"
)
// Stack implementation for the neo-go virtual machine. The stack implements
// a double linked list where its semantics are first in first out.
// To simplify the implementation, internally a Stack s is implemented as a
// ring, such that &s.top is both the next element of the last element s.Back()
// and the previous element of the first element s.Top().
//
// s.Push(0)
// s.Push(1)
// s.Push(2)
//
// [ 2 ] > top
// [ 1 ]
// [ 0 ] > back
//
// s.Pop() > 2
//
// [ 1 ]
// [ 0 ]
// Element represents an element in the double linked list (the stack),
// which will hold the underlying stackitem.Item.
type Element struct {
value stackitem.Item
next, prev *Element
stack *Stack
}
// NewElement returns a new Element object, with its underlying value inferred
// to the corresponding type.
func NewElement(v interface{}) *Element {
return &Element{
value: stackitem.Make(v),
}
}
// Next returns the next element in the stack.
func (e *Element) Next() *Element {
if elem := e.next; e.stack != nil && elem != &e.stack.top {
return elem
}
return nil
}
// Prev returns the previous element in the stack.
func (e *Element) Prev() *Element {
if elem := e.prev; e.stack != nil && elem != &e.stack.top {
return elem
}
return nil
}
// Item returns Item contained in the element.
func (e *Element) Item() stackitem.Item {
return e.value
}
// Value returns value of the Item contained in the element.
func (e *Element) Value() interface{} {
return e.value.Value()
}
// BigInt attempts to get the underlying value of the element as a big integer.
// Will panic if the assertion failed which will be caught by the VM.
func (e *Element) BigInt() *big.Int {
val, err := e.value.TryInteger()
if err != nil {
panic(err)
}
return val
}
// Bool converts an underlying value of the element to a boolean if it's
// possible to do so, it will panic otherwise.
func (e *Element) Bool() bool {
b, err := e.value.TryBool()
if err != nil {
panic(err)
}
return b
}
// Bytes attempts to get the underlying value of the element as a byte array.
// Will panic if the assertion failed which will be caught by the VM.
func (e *Element) Bytes() []byte {
bs, err := e.value.TryBytes()
if err != nil {
panic(err)
}
return bs
}
// BytesOrNil attempts to get the underlying value of the element as a byte array or nil.
// Will panic if the assertion failed which will be caught by the VM.
func (e *Element) BytesOrNil() []byte {
if _, ok := e.value.(stackitem.Null); ok {
return nil
}
bs, err := e.value.TryBytes()
if err != nil {
panic(err)
}
return bs
}
// String attempts to get string from the element value.
// It is assumed to be use in interops and panics if string is not a valid UTF-8 byte sequence.
func (e *Element) String() string {
s, err := stackitem.ToString(e.value)
if err != nil {
panic(err)
}
return s
}
// Array attempts to get the underlying value of the element as an array of
// other items. Will panic if the item type is different which will be caught
// by the VM.
func (e *Element) Array() []stackitem.Item {
switch t := e.value.(type) {
case *stackitem.Array:
return t.Value().([]stackitem.Item)
case *stackitem.Struct:
return t.Value().([]stackitem.Item)
default:
panic("element is not an array")
}
}
// Interop attempts to get the underlying value of the element
// as an interop item.
func (e *Element) Interop() *stackitem.Interop {
switch t := e.value.(type) {
case *stackitem.Interop:
return t
default:
panic("element is not an interop")
}
}
// Stack represents a Stack backed by a double linked list.
type Stack struct {
top Element
name string
len int
refs *refCounter
}
// NewStack returns a new stack name by the given name.
func NewStack(n string) *Stack {
s := &Stack{
name: n,
}
s.top.next = &s.top
s.top.prev = &s.top
s.len = 0
s.refs = newRefCounter()
return s
}
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// Clear clears all elements on the stack and set its length to 0.
func (s *Stack) Clear() {
s.top.next = &s.top
s.top.prev = &s.top
s.len = 0
}
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// Len returns the number of elements that are on the stack.
func (s *Stack) Len() int {
return s.len
}
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// insert inserts the element after element (at) on the stack.
func (s *Stack) insert(e, at *Element) *Element {
// If we insert an element that is already popped from this stack,
// we need to clean it up, there are still pointers referencing to it.
if e.stack == s {
e = NewElement(e.value)
}
n := at.next
at.next = e
e.prev = at
e.next = n
n.prev = e
e.stack = s
s.len++
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s.refs.Add(e.value)
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return e
}
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// InsertAt inserts the given item (n) deep on the stack.
// Be very careful using it and _always_ check both e and n before invocation
// as it will silently do wrong things otherwise.
func (s *Stack) InsertAt(e *Element, n int) *Element {
before := s.Peek(n - 1)
if before == nil {
return nil
}
return s.insert(e, before)
}
// Push pushes the given element on the stack.
func (s *Stack) Push(e *Element) {
s.insert(e, &s.top)
}
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// PushVal pushes the given value on the stack. It will infer the
// underlying Item to its corresponding type.
func (s *Stack) PushVal(v interface{}) {
s.Push(NewElement(v))
}
// Pop removes and returns the element on top of the stack.
func (s *Stack) Pop() *Element {
return s.Remove(s.Top())
}
// Top returns the element on top of the stack. Nil if the stack
// is empty.
func (s *Stack) Top() *Element {
if s.len == 0 {
return nil
}
return s.top.next
}
// Back returns the element at the end of the stack. Nil if the stack
// is empty.
func (s *Stack) Back() *Element {
if s.len == 0 {
return nil
}
return s.top.prev
}
// Peek returns the element (n) far in the stack beginning from
// the top of the stack.
// n = 0 => will return the element on top of the stack.
func (s *Stack) Peek(n int) *Element {
i := 0
for e := s.Top(); e != nil; e = e.Next() {
if n == i {
return e
}
i++
}
return nil
}
// RemoveAt removes the element (n) deep on the stack beginning
// from the top of the stack.
func (s *Stack) RemoveAt(n int) *Element {
return s.Remove(s.Peek(n))
}
// Remove removes and returns the given element from the stack.
func (s *Stack) Remove(e *Element) *Element {
if e == nil {
return nil
}
e.prev.next = e.next
e.next.prev = e.prev
e.next = nil // avoid memory leaks.
e.prev = nil // avoid memory leaks.
e.stack = nil
s.len--
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s.refs.Remove(e.value)
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return e
}
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// Dup duplicates and returns the element at position n.
// Dup is used for copying elements on to the top of its own stack.
// s.Push(s.Peek(0)) // will result in unexpected behaviour.
// s.Push(s.Dup(0)) // is the correct approach.
func (s *Stack) Dup(n int) *Element {
e := s.Peek(n)
if e == nil {
return nil
}
return &Element{
value: e.value.Dup(),
}
}
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// Iter iterates over all the elements int the stack, starting from the top
// of the stack.
// s.Iter(func(elem *Element) {
// // do something with the element.
// })
func (s *Stack) Iter(f func(*Element)) {
for e := s.Top(); e != nil; e = e.Next() {
f(e)
}
}
// IterBack iterates over all the elements of the stack, starting from the bottom
// of the stack.
// s.IterBack(func(elem *Element) {
// // do something with the element.
// })
func (s *Stack) IterBack(f func(*Element)) {
for e := s.Back(); e != nil; e = e.Prev() {
f(e)
}
}
// Swap swaps two elements on the stack without popping and pushing them.
func (s *Stack) Swap(n1, n2 int) error {
if n1 < 0 || n2 < 0 {
return errors.New("negative index")
}
if n1 >= s.len || n2 >= s.len {
return errors.New("too big index")
}
if n1 == n2 {
return nil
}
s.swap(n1, n2)
return nil
}
func (s *Stack) swap(n1, n2 int) {
a := s.Peek(n1)
b := s.Peek(n2)
a.value, b.value = b.value, a.value
}
// ReverseTop reverses top n items of the stack.
func (s *Stack) ReverseTop(n int) error {
if n < 0 {
return errors.New("negative index")
} else if n > s.len {
return errors.New("too big index")
} else if n <= 1 {
return nil
}
a, b := s.Peek(0), s.Peek(n-1)
for i := 0; i < n/2; i++ {
a.value, b.value = b.value, a.value
a = a.Next()
b = b.Prev()
}
return nil
}
// Roll brings an item with the given index to the top of the stack, moving all
// the other elements down accordingly. It does all of that without popping and
// pushing elements.
func (s *Stack) Roll(n int) error {
if n < 0 {
return errors.New("negative index")
}
if n >= s.len {
return errors.New("too big index")
}
if n == 0 {
return nil
}
top := s.Peek(0)
e := s.Peek(n)
e.prev.next = e.next
e.next.prev = e.prev
top.prev = e
e.next = top
e.prev = &s.top
s.top.next = e
return nil
}
// PopSigElements pops keys or signatures from the stack as needed for
// CHECKMULTISIG.
func (s *Stack) PopSigElements() ([][]byte, error) {
var num int
var elems [][]byte
item := s.Pop()
if item == nil {
return nil, fmt.Errorf("nothing on the stack")
}
switch item.value.(type) {
case *stackitem.Array:
num = len(item.Array())
if num < 1 {
return nil, fmt.Errorf("less than one element in the array")
}
elems = make([][]byte, num)
for k, v := range item.Array() {
b, ok := v.Value().([]byte)
if !ok {
return nil, fmt.Errorf("bad element %s", v.String())
}
elems[k] = b
}
default:
num = int(item.BigInt().Int64())
if num < 1 || num > s.Len() {
return nil, fmt.Errorf("wrong number of elements: %d", num)
}
elems = make([][]byte, num)
for i := 0; i < num; i++ {
elems[i] = s.Pop().Bytes()
}
}
return elems, nil
}
// ToArray converts stack to an array of stackitems with top item being the last.
func (s *Stack) ToArray() []stackitem.Item {
items := make([]stackitem.Item, 0, s.len)
s.IterBack(func(e *Element) {
items = append(items, e.Item())
})
return items
}
// MarshalJSON implements JSON marshalling interface.
func (s *Stack) MarshalJSON() ([]byte, error) {
items := s.ToArray()
arr := make([]json.RawMessage, len(items))
for i := range items {
data, err := stackitem.ToJSONWithTypes(items[i])
if err == nil {
arr[i] = data
}
}
return json.Marshal(arr)
}