vm: expose Context slots, hide Set/ClearRefs on Slot, deprecate Dump*Slot methods

Signed-off-by: ixje <erik@coz.io>

ROADMAP.md

@@ -68,4 +68,14 @@ event-based waiter fallbacks to the old way of block monitoring with
 `block_added` notifications subscription.
 
 Removal of stale RPC server compatibility code from `waiter.EventWaiter` is
-scheduled for Jun-Jul 2024 (~0.107.0 release).
+scheduled for Jun-Jul 2024 (~0.107.0 release).
+
+## Dump*Slot() methods of `vm.Context`
+
+The following new methods have been exposed to give access to VM context slot contents
+with greater flexibility:
+- `ArgumentsSlot`
+- `LocalsSlot`
+- `StaticsSlot`.
+
+Removal of the `Dump*Slot()` methods are scheduled for the 0.108.0 release.

cli/vm/cli.go

@@ -648,11 +648,11 @@ func handleSlots(c *cli.Context) error {
 	var rawSlot string
 	switch c.Command.Name {
 	case "sslot":
-		rawSlot = vmCtx.DumpStaticSlot()
+		rawSlot = dumpSlot(vmCtx.StaticsSlot())
 	case "lslot":
-		rawSlot = vmCtx.DumpLocalSlot()
+		rawSlot = dumpSlot(vmCtx.LocalsSlot())
 	case "aslot":
-		rawSlot = vmCtx.DumpArgumentsSlot()
+		rawSlot = dumpSlot(vmCtx.ArgumentsSlot())
 	default:
 		return errors.New("unknown slot")
 	}
@@ -660,6 +660,14 @@ func handleSlots(c *cli.Context) error {
 	return nil
 }
 
+func dumpSlot(s *vm.Slot) string {
+	if s == nil {
+		return "[]"
+	}
+	b, _ := json.MarshalIndent(s, "", "    ")
+	return string(b)
+}
+
 // prepareVM retrieves --historic flag from context (if set) and resets app state
 // (to the specified historic height if given).
 func prepareVM(c *cli.Context, tx *transaction.Transaction) error {

pkg/vm/context.go

@@ -30,7 +30,7 @@ type scriptContext struct {
 	// Evaluation stack pointer.
 	estack *Stack
 
-	static slot
+	static Slot
 
 	// Script hash of the prog.
 	scriptHash util.Uint160
@@ -65,8 +65,8 @@ type Context struct {
 
 	sc *scriptContext
 
-	local     slot
-	arguments slot
+	local     Slot
+	arguments Slot
 
 	// Exception context stack.
 	tryStack Stack
@@ -278,22 +278,26 @@ func (c *Context) IsDeployed() bool {
 }
 
 // DumpStaticSlot returns json formatted representation of the given slot.
+// Deprecated: to be removed in next version. Use [Context.StaticsSlot] instead.
 func (c *Context) DumpStaticSlot() string {
 	return dumpSlot(&c.sc.static)
 }
 
 // DumpLocalSlot returns json formatted representation of the given slot.
+// Deprecated: to be removed in next version. Use [Context.LocalsSlot] instead.
 func (c *Context) DumpLocalSlot() string {
 	return dumpSlot(&c.local)
 }
 
 // DumpArgumentsSlot returns json formatted representation of the given slot.
+// Deprecated: to be removed in next version. Use [Context.ArgumentsSlot] instead.
 func (c *Context) DumpArgumentsSlot() string {
 	return dumpSlot(&c.arguments)
 }
 
 // dumpSlot returns json formatted representation of the given slot.
-func dumpSlot(s *slot) string {
+// Deprecated: to be removed in next version.
+func dumpSlot(s *Slot) string {
 	if s == nil || *s == nil {
 		return "[]"
 	}
@@ -354,3 +358,18 @@ func DynamicOnUnload(v *VM, ctx *Context, commit bool) error {
 func (c *Context) BreakPoints() []int {
 	return slices.Clone(c.sc.breakPoints)
 }
+
+// ArgumentsSlot returns the arguments slot of Context.
+func (c *Context) ArgumentsSlot() *Slot {
+	return &c.arguments
+}
+
+// LocalsSlot returns the local slot of Context.
+func (c *Context) LocalsSlot() *Slot {
+	return &c.local
+}
+
+// StaticsSlot returns the static slot of Context.
+func (c *Context) StaticsSlot() *Slot {
+	return &c.sc.static
+}

pkg/vm/json_test.go

@@ -240,7 +240,7 @@ func compareStacks(t *testing.T, expected []vmUTStackItem, actual *Stack) {
 	compareItemArrays(t, expected, actual.Len(), func(i int) stackitem.Item { return actual.Peek(i).Item() })
 }
 
-func compareSlots(t *testing.T, expected []vmUTStackItem, actual slot) {
+func compareSlots(t *testing.T, expected []vmUTStackItem, actual Slot) {
 	if actual == nil && len(expected) == 0 {
 		return
 	}

pkg/vm/slot.go

@@ -6,11 +6,11 @@ import (
 	"github.com/nspcc-dev/neo-go/pkg/vm/stackitem"
 )
 
-// slot is a fixed-size slice of stack items.
-type slot []stackitem.Item
+// Slot is a fixed-size slice of stack items.
+type Slot []stackitem.Item
 
 // init sets static slot size to n. It is intended to be used only by INITSSLOT.
-func (s *slot) init(n int, rc *refCounter) {
+func (s *Slot) init(n int, rc *refCounter) {
 	if *s != nil {
 		panic("already initialized")
 	}
@@ -18,8 +18,8 @@ func (s *slot) init(n int, rc *refCounter) {
 	*rc += refCounter(n) // Virtual "Null" elements.
 }
 
-// Set sets i-th storage slot.
-func (s slot) Set(i int, item stackitem.Item, refs *refCounter) {
+// set sets i-th storage slot.
+func (s Slot) set(i int, item stackitem.Item, refs *refCounter) {
 	if s[i] == item {
 		return
 	}
@@ -29,30 +29,30 @@ func (s slot) Set(i int, item stackitem.Item, refs *refCounter) {
 }
 
 // Get returns the item contained in the i-th slot.
-func (s slot) Get(i int) stackitem.Item {
+func (s Slot) Get(i int) stackitem.Item {
 	if item := s[i]; item != nil {
 		return item
 	}
 	return stackitem.Null{}
 }
 
-// ClearRefs removes all slot variables from the reference counter.
-func (s slot) ClearRefs(refs *refCounter) {
+// clearRefs removes all slot variables from the reference counter.
+func (s Slot) clearRefs(refs *refCounter) {
 	for _, item := range s {
 		refs.Remove(item)
 	}
 }
 
 // Size returns the slot size.
-func (s slot) Size() int {
+func (s Slot) Size() int {
 	if s == nil {
-		panic("not initialized")
+		return 0
 	}
 	return len(s)
 }
 
 // MarshalJSON implements the JSON marshalling interface.
-func (s slot) MarshalJSON() ([]byte, error) {
+func (s Slot) MarshalJSON() ([]byte, error) {
 	arr := make([]json.RawMessage, len(s))
 	for i := range s {
 		data, err := stackitem.ToJSONWithTypes(s[i])

pkg/vm/slot_test.go

@@ -10,8 +10,8 @@ import (
 
 func TestSlot_Get(t *testing.T) {
 	rc := newRefCounter()
-	var s slot
-	require.Panics(t, func() { s.Size() })
+	var s Slot
+	require.Equal(t, 0, s.Size())
 
 	s.init(3, rc)
 	require.Equal(t, 3, s.Size())
@@ -21,7 +21,7 @@ func TestSlot_Get(t *testing.T) {
 	item := s.Get(2)
 	require.Equal(t, stackitem.Null{}, item)
 
-	s.Set(1, stackitem.NewBigInteger(big.NewInt(42)), rc)
+	s.set(1, stackitem.NewBigInteger(big.NewInt(42)), rc)
 	require.Equal(t, stackitem.NewBigInteger(big.NewInt(42)), s.Get(1))
 	require.Equal(t, 3, int(*rc))
 }

pkg/vm/vm.go

@@ -697,7 +697,7 @@ func (v *VM) execute(ctx *Context, op opcode.Opcode, parameter []byte) (err erro
 			sz := int(parameter[1])
 			ctx.arguments.init(sz, &v.refs)
 			for i := range sz {
-				ctx.arguments.Set(i, v.estack.Pop().Item(), &v.refs)
+				ctx.arguments.set(i, v.estack.Pop().Item(), &v.refs)
 			}
 		}
 
@@ -711,11 +711,11 @@ func (v *VM) execute(ctx *Context, op opcode.Opcode, parameter []byte) (err erro
 
 	case opcode.STSFLD0, opcode.STSFLD1, opcode.STSFLD2, opcode.STSFLD3, opcode.STSFLD4, opcode.STSFLD5, opcode.STSFLD6:
 		item := v.estack.Pop().Item()
-		ctx.sc.static.Set(int(op-opcode.STSFLD0), item, &v.refs)
+		ctx.sc.static.set(int(op-opcode.STSFLD0), item, &v.refs)
 
 	case opcode.STSFLD:
 		item := v.estack.Pop().Item()
-		ctx.sc.static.Set(int(parameter[0]), item, &v.refs)
+		ctx.sc.static.set(int(parameter[0]), item, &v.refs)
 
 	case opcode.LDLOC0, opcode.LDLOC1, opcode.LDLOC2, opcode.LDLOC3, opcode.LDLOC4, opcode.LDLOC5, opcode.LDLOC6:
 		item := ctx.local.Get(int(op - opcode.LDLOC0))
@@ -727,11 +727,11 @@ func (v *VM) execute(ctx *Context, op opcode.Opcode, parameter []byte) (err erro
 
 	case opcode.STLOC0, opcode.STLOC1, opcode.STLOC2, opcode.STLOC3, opcode.STLOC4, opcode.STLOC5, opcode.STLOC6:
 		item := v.estack.Pop().Item()
-		ctx.local.Set(int(op-opcode.STLOC0), item, &v.refs)
+		ctx.local.set(int(op-opcode.STLOC0), item, &v.refs)
 
 	case opcode.STLOC:
 		item := v.estack.Pop().Item()
-		ctx.local.Set(int(parameter[0]), item, &v.refs)
+		ctx.local.set(int(parameter[0]), item, &v.refs)
 
 	case opcode.LDARG0, opcode.LDARG1, opcode.LDARG2, opcode.LDARG3, opcode.LDARG4, opcode.LDARG5, opcode.LDARG6:
 		item := ctx.arguments.Get(int(op - opcode.LDARG0))
@@ -743,11 +743,11 @@ func (v *VM) execute(ctx *Context, op opcode.Opcode, parameter []byte) (err erro
 
 	case opcode.STARG0, opcode.STARG1, opcode.STARG2, opcode.STARG3, opcode.STARG4, opcode.STARG5, opcode.STARG6:
 		item := v.estack.Pop().Item()
-		ctx.arguments.Set(int(op-opcode.STARG0), item, &v.refs)
+		ctx.arguments.set(int(op-opcode.STARG0), item, &v.refs)
 
 	case opcode.STARG:
 		item := v.estack.Pop().Item()
-		ctx.arguments.Set(int(parameter[0]), item, &v.refs)
+		ctx.arguments.set(int(parameter[0]), item, &v.refs)
 
 	case opcode.NEWBUFFER:
 		n := toInt(v.estack.Pop().BigInt())
@@ -1692,15 +1692,15 @@ func (v *VM) execute(ctx *Context, op opcode.Opcode, parameter []byte) (err erro
 
 func (v *VM) unloadContext(ctx *Context) {
 	if ctx.local != nil {
-		ctx.local.ClearRefs(&v.refs)
+		ctx.local.clearRefs(&v.refs)
 	}
 	if ctx.arguments != nil {
-		ctx.arguments.ClearRefs(&v.refs)
+		ctx.arguments.clearRefs(&v.refs)
 	}
 	currCtx := v.Context()
 	if currCtx == nil || ctx.sc != currCtx.sc {
 		if ctx.sc.static != nil {
-			ctx.sc.static.ClearRefs(&v.refs)
+			ctx.sc.static.clearRefs(&v.refs)
 		}
 		if ctx.sc.onUnload != nil {
 			err := ctx.sc.onUnload(v, ctx, v.uncaughtException == nil)