fix: http download fail (#61)

ui/flutter/lib/api/model/request.dart

@@ -2,17 +2,31 @@ import 'package:json_annotation/json_annotation.dart';
 
 part 'request.g.dart';
 
-@JsonSerializable()
+@JsonSerializable(explicitToJson: true, genericArgumentFactories: true)
 class Request {
   String url;
   Map<String, dynamic>? extra;
 
   Request({
     required this.url,
-    this.extra,
   });
 
   factory Request.fromJson(Map<String, dynamic> json) =>
       _$RequestFromJson(json);
+
   Map<String, dynamic> toJson() => _$RequestToJson(this);
 }
+
+@JsonSerializable()
+class ReqExtraHttp {
+  String method = 'GET';
+  Map<String, String> headers = {};
+  String body = '';
+
+  ReqExtraHttp();
+
+  factory ReqExtraHttp.fromJson(Map<String, dynamic> json) =>
+      _$ReqExtraHttpFromJson(json);
+
+  Map<String, dynamic> toJson() => _$ReqExtraHttpToJson(this);
+}