core: implement System.Callback.* interops

Support creating callbacks from pointers.

Signed-off-by: Evgenii Stratonikov <evgeniy@nspcc.ru>

pkg/core/interop/callback/callback.go

@@ -0,0 +1,28 @@
+package callback
+
+import (
+	"errors"
+
+	"github.com/nspcc-dev/neo-go/pkg/core/interop"
+	"github.com/nspcc-dev/neo-go/pkg/vm"
+	"github.com/nspcc-dev/neo-go/pkg/vm/stackitem"
+)
+
+// Callback is an interface for arbitrary callbacks.
+type Callback interface {
+	// ArgCount returns expected number of arguments.
+	ArgCount() int
+	// LoadContext loads context and arguments on stack.
+	LoadContext(*vm.VM, []stackitem.Item)
+}
+
+// Invoke invokes provided callback.
+func Invoke(_ *interop.Context, v *vm.VM) error {
+	cb := v.Estack().Pop().Interop().Value().(Callback)
+	args := v.Estack().Pop().Array()
+	if cb.ArgCount() != len(args) {
+		return errors.New("invalid argument count")
+	}
+	cb.LoadContext(v, args)
+	return nil
+}

pkg/core/interop/callback/pointer.go

@@ -0,0 +1,42 @@
+package callback
+
+import (
+	"github.com/nspcc-dev/neo-go/pkg/core/interop"
+	"github.com/nspcc-dev/neo-go/pkg/vm"
+	"github.com/nspcc-dev/neo-go/pkg/vm/stackitem"
+)
+
+// PointerCallback represents callback for a pointer.
+type PointerCallback struct {
+	paramCount int
+	offset     int
+	context    *vm.Context
+}
+
+var _ Callback = (*PointerCallback)(nil)
+
+// ArgCount implements Callback interface.
+func (p *PointerCallback) ArgCount() int {
+	return p.paramCount
+}
+
+// LoadContext implements Callback interface.
+func (p *PointerCallback) LoadContext(v *vm.VM, args []stackitem.Item) {
+	v.Call(p.context, p.offset)
+	for i := len(args) - 1; i >= 0; i-- {
+		v.Estack().PushVal(args[i])
+	}
+}
+
+// Create creates callback using pointer and parameters count.
+func Create(_ *interop.Context, v *vm.VM) error {
+	ctx := v.Estack().Pop().Item().(*vm.Context)
+	offset := v.Estack().Pop().Item().(*stackitem.Pointer).Position()
+	count := v.Estack().Pop().BigInt().Int64()
+	v.Estack().PushVal(stackitem.NewInterop(&PointerCallback{
+		paramCount: int(count),
+		offset:     offset,
+		context:    ctx,
+	}))
+	return nil
+}

pkg/core/interop_system_test.go

@@ -6,6 +6,7 @@ import (
 
 	"github.com/nspcc-dev/dbft/crypto"
 	"github.com/nspcc-dev/neo-go/pkg/config/netmode"
+	"github.com/nspcc-dev/neo-go/pkg/core/interop/callback"
 	"github.com/nspcc-dev/neo-go/pkg/core/interop/runtime"
 	"github.com/nspcc-dev/neo-go/pkg/core/state"
 	"github.com/nspcc-dev/neo-go/pkg/core/transaction"
@@ -733,3 +734,38 @@ func TestContractGetCallFlags(t *testing.T) {
 	require.NoError(t, contractGetCallFlags(ic, v))
 	require.Equal(t, int64(smartcontract.All), v.Estack().Pop().Value().(*big.Int).Int64())
 }
+
+func TestPointerCallback(t *testing.T) {
+	_, ic, bc := createVM(t)
+	defer bc.Close()
+
+	script := []byte{
+		byte(opcode.NOP), byte(opcode.INC), byte(opcode.RET),
+		byte(opcode.DIV), byte(opcode.RET),
+	}
+	t.Run("Good", func(t *testing.T) {
+		v := loadScript(script, 2, stackitem.NewPointer(3, script))
+		v.Estack().PushVal(v.Context())
+		require.NoError(t, callback.Create(ic, v))
+
+		args := stackitem.NewArray([]stackitem.Item{stackitem.Make(3), stackitem.Make(12)})
+		v.Estack().InsertAt(vm.NewElement(args), 1)
+		require.NoError(t, callback.Invoke(ic, v))
+
+		require.NoError(t, v.Run())
+		require.Equal(t, 1, v.Estack().Len())
+		require.Equal(t, big.NewInt(5), v.Estack().Pop().Item().Value())
+	})
+	t.Run("Invalid", func(t *testing.T) {
+		t.Run("NotEnoughParameters", func(t *testing.T) {
+			v := loadScript(script, 2, stackitem.NewPointer(3, script))
+			v.Estack().PushVal(v.Context())
+			require.NoError(t, callback.Create(ic, v))
+
+			args := stackitem.NewArray([]stackitem.Item{stackitem.Make(3)})
+			v.Estack().InsertAt(vm.NewElement(args), 1)
+			require.Error(t, callback.Invoke(ic, v))
+		})
+	})
+
+}

pkg/core/interops.go

@@ -9,6 +9,7 @@ package core
 
 import (
 	"github.com/nspcc-dev/neo-go/pkg/core/interop"
+	"github.com/nspcc-dev/neo-go/pkg/core/interop/callback"
 	"github.com/nspcc-dev/neo-go/pkg/core/interop/crypto"
 	"github.com/nspcc-dev/neo-go/pkg/core/interop/enumerator"
 	"github.com/nspcc-dev/neo-go/pkg/core/interop/iterator"
@@ -40,6 +41,8 @@ var systemInterops = []interop.Function{
 	{Name: "System.Blockchain.GetTransaction", Func: bcGetTransaction, Price: 1000000, RequiredFlags: smartcontract.AllowStates},
 	{Name: "System.Blockchain.GetTransactionFromBlock", Func: bcGetTransactionFromBlock, Price: 1000000, RequiredFlags: smartcontract.AllowStates},
 	{Name: "System.Blockchain.GetTransactionHeight", Func: bcGetTransactionHeight, Price: 1000000, RequiredFlags: smartcontract.AllowStates},
+	{Name: "System.Callback.Create", Func: callback.Create, Price: 400},
+	{Name: "System.Callback.Invoke", Func: callback.Invoke, Price: 1000000},
 	{Name: "System.Contract.Call", Func: contractCall, Price: 1000000, RequiredFlags: smartcontract.AllowCall},
 	{Name: "System.Contract.CallEx", Func: contractCallEx, Price: 1000000, RequiredFlags: smartcontract.AllowCall},
 	{Name: "System.Contract.Create", Func: contractCreate, Price: 0, RequiredFlags: smartcontract.AllowModifyStates},