Misleading error response when JSON data can not be composed

[liquidiert]

Package

dio

Version

5.4.3+1

Operating-System

Windows

Adapter

Default Dio

Output of flutter doctor -v

[√] Flutter (Channel stable, 3.24.3, on Microsoft Windows [Version 10.0.22631.4317], locale
    en-US)
    • Flutter version 3.24.3 on channel stable at
      C:\Users\redacted\.version-fox\cache\flutter\v-3.24.3\flutter-3.24.3
    • Upstream repository https://github.com/flutter/flutter.git
    • Framework revision 2663184aa7 (8 weeks ago), 2024-09-11 16:27:48 -0500
    • Engine revision 36335019a8
    • Dart version 3.5.3
    • DevTools version 2.37.3

[√] Windows Version (Installed version of Windows is version 10 or higher)

[√] Android toolchain - develop for Android devices (Android SDK version 35.0.0)
    • Android SDK at C:\Users\redacted\Android\android-sdk
    • Platform android-35, build-tools 35.0.0
    • Java binary at: C:\Users\redacted\.version-fox\cache\java\current\bin\java
    • Java version OpenJDK Runtime Environment (build 17.0.2+8-86)
    • All Android licenses accepted.

[√] Chrome - develop for the web
    • Chrome at C:\Program Files\Google\Chrome\Application\chrome.exe

[√] Visual Studio - develop Windows apps (Visual Studio Community 2022 17.10.5)
    • Visual Studio at C:\Program Files\Microsoft Visual Studio\2022\Community
    • Visual Studio Community 2022 version 17.10.35122.118
    • Windows 10 SDK version 10.0.22621.0

[!] Android Studio (not installed)
    • Android Studio not found; download from https://developer.android.com/studio/index.html  
      (or visit https://flutter.dev/to/windows-android-setup for detailed instructions).       

[√] VS Code (version 1.95.0-insider)
    • VS Code at C:\Users\redacted\AppData\Local\Programs\Microsoft VS Code Insiders
    • Flutter extension version 3.99.20240930

[√] Connected device (3 available)
    • Windows (desktop) • windows • windows-x64    • Microsoft Windows [Version
      10.0.22631.4317]
    • Chrome (web)      • chrome  • web-javascript • Google Chrome 130.0.6723.117
    • Edge (web)        • edge    • web-javascript • Microsoft Edge 130.0.2849.68

[√] Network resources
    • All expected network resources are available.

Dart Version

3.5.3

Steps to Reproduce

Was told in #2322 that you do not manipulate error codes. Thus I want to open a bug report stating, that it is misleading to get a 500 exception when Dio failed to compose a valid JSON object.

Steps to reproduce

1. Create a class with a faulty toJson method:

class DeleteFolder {
  final String root;
  final List<DeleteFolderEntry> entries;

  const DeleteFolder({
    required this.root,
    required this.entries,
  });

  factory DeleteFolder.fromJson(Map<String, dynamic> json) {
    return DeleteFolder(
      root: json["root"],
      entries:
          json["entries"].map((e) => DeleteFolderEntry.fromJson(e)).toList(),
    );
  }

  Map<String, dynamic> toJson() {
    return {
      "root": root,
      "entries": entries
          .map(
            (e) => e.toJson(),
          ), // toList() is missing -> throws an exception like can't use MapEntry as Iterable  
    };
  }
}

2. fire for example a POST request to your next available API

Expected Result

Dio should respond with a different status code in this case. Maybe 499 so the developer knows it's the clients fault.

Actual Result

Just a Dio exception with a status code 500. When you activate the logging interceptor it outputs the JSON compose error. That helped me solve my problem but I still think a different status code should be used.

[AlexV525]

Could you provide a minimal runnable example so we can directly run and reproduce your issue?

[liquidiert]

@AlexV525 sure here it is. The logger interceptor outputs the following:

flutter: *** Request ***
flutter: uri: http://localhost:8000
flutter: method: POST
flutter: responseType: ResponseType.json
flutter: followRedirects: true
flutter: persistentConnection: true
flutter: connectTimeout: null
flutter: sendTimeout: null
flutter: receiveTimeout: null
flutter: receiveDataWhenStatusError: true
flutter: extra: {}
flutter: headers:
flutter:  content-type: application/json
flutter: data:
flutter: Instance of 'Test'
flutter:
flutter: *** DioException ***:
[ERROR:flutter/runtime/dart_vm_initializer.cc(41)] Unhandled Exception: DioException [unknown]: null
Error: Converting object to an encodable object failed: Instance of 'Test'
#0      DioMixin.fetch (package:dio/src/dio_mixin.dart:520:7)
<asynchronous suspension>

flutter: uri: http://localhost:8000
flutter: DioException [unknown]: null
Error: Converting object to an encodable object failed: Instance of 'Test'

But the base exception has a status code of 500.
Also you don't need an API running

[AlexV525]

But the base exception has a status code of 500. Also you don't need an API running

What is the base exception you are indicating?

[liquidiert]

The exception dio throws in case something is wrong with the response

[AlexV525]

Your log does not tell 500, and neither your example does. The log interceptor only tells that the conversion error happens.

[liquidiert]

Try to remove the log interceptor :)

[AlexV525]

[AlexV525]

Again, we don't manipulate the response. It is very likely that the 500 returned from your server, rather than this library.