core: add System.Binary.Base64Decode interop

Part of #1055

pkg/core/interop_neo.go

@@ -161,3 +161,14 @@ func runtimeEncode(_ *interop.Context, v *vm.VM) error {
 	v.Estack().PushVal([]byte(result))
 	return nil
 }
+
+// runtimeDecode decodes top stack item from base64 string to byte array.
+func runtimeDecode(_ *interop.Context, v *vm.VM) error {
+	src := string(v.Estack().Pop().Bytes())
+	result, err := base64.StdEncoding.DecodeString(src)
+	if err != nil {
+		return err
+	}
+	v.Estack().PushVal(result)
+	return nil
+}

pkg/core/interop_neo_test.go

@@ -228,6 +228,26 @@ func TestRuntimeEncode(t *testing.T) {
 	require.Equal(t, expected, actual)
 }
 
+func TestRuntimeDecode(t *testing.T) {
+	expected := []byte("my pretty string")
+	str := base64.StdEncoding.EncodeToString(expected)
+	v, ic, bc := createVM(t)
+	defer bc.Close()
+
+	t.Run("positive", func(t *testing.T) {
+		v.Estack().PushVal(str)
+		require.NoError(t, runtimeDecode(ic, v))
+
+		actual := v.Estack().Pop().Bytes()
+		require.Equal(t, expected, actual)
+	})
+
+	t.Run("error", func(t *testing.T) {
+		v.Estack().PushVal(str + "%")
+		require.Error(t, runtimeDecode(ic, v))
+	})
+}
+
 // Helper functions to create VM, InteropContext, TX, Account, Contract.
 
 func createVM(t *testing.T) (*vm.VM, *interop.Context, *Blockchain) {

pkg/core/interops.go

@@ -72,6 +72,7 @@ var systemInterops = []interop.Function{
 	{Name: "System.Binary.Deserialize", Func: runtimeDeserialize, Price: 500000},
 	{Name: "System.Binary.Serialize", Func: runtimeSerialize, Price: 100000},
 	{Name: "System.Binary.Base64Encode", Func: runtimeEncode, Price: 100000},
+	{Name: "System.Binary.Base64Decode", Func: runtimeDecode, Price: 100000},
 	{Name: "System.Blockchain.GetBlock", Func: bcGetBlock, Price: 2500000,
 		AllowedTriggers: trigger.Application, RequiredFlags: smartcontract.AllowStates},
 	{Name: "System.Blockchain.GetContract", Func: bcGetContract, Price: 1000000,