badjson: Improve omitempty

common/json/badjson/array.go

@@ -3,12 +3,25 @@ package badjson
 import (
 	"bytes"
 
+	"github.com/sagernet/sing/common"
 	E "github.com/sagernet/sing/common/exceptions"
 	"github.com/sagernet/sing/common/json"
 )
 
 type JSONArray []any
 
+func (a JSONArray) IsEmpty() bool {
+	if len(a) == 0 {
+		return true
+	}
+	return common.All(a, func(it any) bool {
+		if valueInterface, valueMaybeEmpty := it.(isEmpty); valueMaybeEmpty && valueInterface.IsEmpty() {
+			return true
+		}
+		return false
+	})
+}
+
 func (a JSONArray) MarshalJSON() ([]byte, error) {
 	return json.Marshal([]any(a))
 }

common/json/badjson/empty.go

@@ -0,0 +1,5 @@
+package badjson
+
+type isEmpty interface {
+	IsEmpty() bool
+}

common/json/badjson/object.go

@@ -15,11 +15,23 @@ type JSONObject struct {
 	linkedhashmap.Map[string, any]
 }
 
-func (m JSONObject) MarshalJSON() ([]byte, error) {
+func (m *JSONObject) IsEmpty() bool {
+	if m.Size() == 0 {
+		return true
+	}
+	return common.All(m.Entries(), func(it collections.MapEntry[string, any]) bool {
+		if valueInterface, valueMaybeEmpty := it.Value.(isEmpty); valueMaybeEmpty && valueInterface.IsEmpty() {
+			return true
+		}
+		return false
+	})
+}
+
+func (m *JSONObject) MarshalJSON() ([]byte, error) {
 	buffer := new(bytes.Buffer)
 	buffer.WriteString("{")
 	items := common.Filter(m.Entries(), func(it collections.MapEntry[string, any]) bool {
-		if valueObject, valueIsJSONObject := it.Value.(*JSONObject); valueIsJSONObject && valueObject.IsEmpty() {
+		if valueInterface, valueMaybeEmpty := it.Value.(isEmpty); valueMaybeEmpty && valueInterface.IsEmpty() {
 			return false
 		}
 		return true