package vm import ( "encoding/json" "errors" "fmt" "math/big" "github.com/nspcc-dev/neo-go/pkg/smartcontract" ) // 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. type Element struct { value StackItem 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: makeStackItem(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 StackItem contained in the element. func (e *Element) Item() StackItem { return e.value } // Value returns value of the StackItem 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. func (e *Element) Bool() bool { return e.value.Bool() } // 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 } // 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 { switch t := e.value.(type) { case *ArrayItem: return t.value case *StructItem: return t.value 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() *InteropItem { switch t := e.value.(type) { case *InteropItem: 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 } // 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 } // Len returns the number of elements that are on the stack. func (s *Stack) Len() int { return s.len } // 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++ s.refs.Add(e.value) return e } // 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) } // PushVal pushes the given value on the stack. It will infer the // underlying StackItem 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-- s.refs.Remove(e.value) return e } // 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(), } } // 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 } for i, j := 0, n-1; i < j; { s.swap(i, j) i++ j-- } 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 *ArrayItem: 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 } // ToContractParameters converts Stack to slice of smartcontract.Parameter. func (s *Stack) ToContractParameters() []smartcontract.Parameter { items := make([]smartcontract.Parameter, 0, s.Len()) s.IterBack(func(e *Element) { // Each item is independent. seen := make(map[StackItem]bool) items = append(items, e.value.ToContractParameter(seen)) }) return items } // MarshalJSON implements JSON marshalling interface. func (s *Stack) MarshalJSON() ([]byte, error) { return json.Marshal(s.ToContractParameters()) }