added json unmarshaler for castTo (#1825)

* added json unmarshaler for castTo

* added json unmarshaler for castTo tests

* json unmarshaler castTo CHANGELOG.md description

---------

Co-authored-by: Aleksey Myasnikov <[email protected]>

Author: flymedllva

CHANGELOG.md

@@ -1,3 +1,4 @@
+* Added support for the `json.Unmarshaler` interface in the `CastTo` function for use in scanners, such as the `ScanStruct` method
 * Fixed the support of server-side session balancing in `database/sql` driver
 * Added `ydb.WithDisableSessionBalancer()` driver option for disable server-side session balancing on table and query clients
 

internal/value/cast_test.go

@@ -2,6 +2,8 @@ package value
 
 import (
 	"database/sql/driver"
+	"encoding/json"
+	"errors"
 	"reflect"
 	"testing"
 	"time"
@@ -25,6 +27,28 @@ func unwrapPtr(v interface{}) interface{} {
 	return reflect.ValueOf(v).Elem().Interface()
 }
 
+type jsonUnmarshaller struct {
+	bytes []byte
+}
+
+func (json *jsonUnmarshaller) UnmarshalJSON(bytes []byte) error {
+	json.bytes = bytes
+
+	return nil
+}
+
+var _ json.Unmarshaler = &jsonUnmarshaller{}
+
+type jsonUnmarshallerBroken struct {
+	bytes []byte
+}
+
+func (json *jsonUnmarshallerBroken) UnmarshalJSON(_ []byte) error {
+	return errors.New("unmarshal error")
+}
+
+var _ json.Unmarshaler = &jsonUnmarshallerBroken{}
+
 func loadLocation(t *testing.T, name string) *time.Location {
 	loc, err := time.LoadLocation(name)
 	require.NoError(t, err)
@@ -138,6 +162,75 @@ func TestCastTo(t *testing.T) {
 			err:   ErrCannotCast,
 		},
 
+		// JSONValue
+		{
+			name:  xtest.CurrentFileLine(),
+			value: JSONValue(`{"test": "text"}"`),
+			dst:   ptr[string](),
+			exp:   `{"test": "text"}"`,
+			err:   nil,
+		},
+		{
+			name:  xtest.CurrentFileLine(),
+			value: JSONValue(`{"test":"text"}"`),
+			dst:   ptr[Value](),
+			exp:   JSONValue(`{"test":"text"}"`),
+			err:   nil,
+		},
+		{
+			name:  xtest.CurrentFileLine(),
+			value: OptionalValue(JSONValue(`{"test": "text"}"`)),
+			dst:   ptr[*[]byte](),
+			exp:   value2ptr([]byte(`{"test": "text"}"`)),
+			err:   nil,
+		},
+		{
+			name:  xtest.CurrentFileLine(),
+			value: JSONValue(`{"test":"text"}"`),
+			dst:   ptr[[]byte](),
+			exp:   []byte(`{"test":"text"}"`),
+			err:   nil,
+		},
+		{
+			name:  xtest.CurrentFileLine(),
+			value: JSONValue(`{"test": "text"}"`),
+			dst:   ptr[jsonUnmarshaller](),
+			exp:   jsonUnmarshaller{[]byte(`{"test": "text"}"`)},
+			err:   nil,
+		},
+		{
+			name:  xtest.CurrentFileLine(),
+			value: JSONValue(`{"test": "text"}"`),
+			dst:   ptr[jsonUnmarshallerBroken](),
+			err:   ErrCannotCast,
+		},
+		{
+			name:  xtest.CurrentFileLine(),
+			value: OptionalValue(JSONValue(`{"test": "text"}"`)),
+			dst:   ptr[jsonUnmarshaller](),
+			exp:   jsonUnmarshaller{[]byte(`{"test": "text"}"`)},
+			err:   nil,
+		},
+		{
+			name:  xtest.CurrentFileLine(),
+			value: OptionalValue(JSONValue(`{"test": "text"}"`)),
+			dst:   ptr[jsonUnmarshallerBroken](),
+			err:   ErrCannotCast,
+		},
+		{
+			name:  xtest.CurrentFileLine(),
+			value: JSONValue(`{"test": "text"}"`),
+			dst:   ptr[int](),
+			err:   ErrCannotCast,
+		},
+		{
+			name:  xtest.CurrentFileLine(),
+			value: OptionalValue(JSONValue(`{"test": "text"}"`)),
+			dst:   ptr[int](),
+			err:   ErrCannotCast,
+		},
+
+		// JSONDocumentValue
 		{
 			name:  xtest.CurrentFileLine(),
 			value: JSONDocumentValue(`{"test": "text"}"`),
@@ -166,6 +259,44 @@ func TestCastTo(t *testing.T) {
 			exp:   []byte(`{"test":"text"}"`),
 			err:   nil,
 		},
+		{
+			name:  xtest.CurrentFileLine(),
+			value: JSONDocumentValue(`{"test": "text"}"`),
+			dst:   ptr[jsonUnmarshaller](),
+			exp:   jsonUnmarshaller{[]byte(`{"test": "text"}"`)},
+			err:   nil,
+		},
+		{
+			name:  xtest.CurrentFileLine(),
+			value: JSONDocumentValue(`{"test": "text"}"`),
+			dst:   ptr[jsonUnmarshallerBroken](),
+			err:   ErrCannotCast,
+		},
+		{
+			name:  xtest.CurrentFileLine(),
+			value: OptionalValue(JSONDocumentValue(`{"test": "text"}"`)),
+			dst:   ptr[jsonUnmarshaller](),
+			exp:   jsonUnmarshaller{[]byte(`{"test": "text"}"`)},
+			err:   nil,
+		},
+		{
+			name:  xtest.CurrentFileLine(),
+			value: OptionalValue(JSONDocumentValue(`{"test": "text"}"`)),
+			dst:   ptr[jsonUnmarshallerBroken](),
+			err:   ErrCannotCast,
+		},
+		{
+			name:  xtest.CurrentFileLine(),
+			value: JSONDocumentValue(`{"test": "text"}"`),
+			dst:   ptr[int](),
+			err:   ErrCannotCast,
+		},
+		{
+			name:  xtest.CurrentFileLine(),
+			value: OptionalValue(JSONDocumentValue(`{"test": "text"}"`)),
+			dst:   ptr[int](),
+			err:   ErrCannotCast,
+		},
 
 		{
 			name:  xtest.CurrentFileLine(),

internal/value/value.go

@@ -3,6 +3,7 @@ package value
 import (
 	"database/sql/driver"
 	"encoding/binary"
+	"encoding/json"
 	"fmt"
 	"math/big"
 	"reflect"
@@ -1369,6 +1370,16 @@ func (v jsonValue) castTo(dst any) error {
 	case *[]byte:
 		*vv = xstring.ToBytes(string(v))
 
+		return nil
+	case json.Unmarshaler:
+		err := vv.UnmarshalJSON(xstring.ToBytes(string(v)))
+		if err != nil {
+			return xerrors.WithStackTrace(fmt.Errorf(
+				"%w '%s(%+v)' to '%T' destination: %w",
+				ErrCannotCast, v.Type().Yql(), v, vv, err,
+			))
+		}
+
 		return nil
 	default:
 		return xerrors.WithStackTrace(fmt.Errorf(
@@ -1413,6 +1424,16 @@ func (v jsonDocumentValue) castTo(dst any) error {
 	case *[]byte:
 		*vv = xstring.ToBytes(string(v))
 
+		return nil
+	case json.Unmarshaler:
+		err := vv.UnmarshalJSON(xstring.ToBytes(string(v)))
+		if err != nil {
+			return xerrors.WithStackTrace(fmt.Errorf(
+				"%w '%s(%+v)' to '%T' destination: %w",
+				ErrCannotCast, v.Type().Yql(), v, vv, err,
+			))
+		}
+
 		return nil
 	default:
 		return xerrors.WithStackTrace(fmt.Errorf(