json_shield 0.1.0

Dependency-free JSON decoding guard for fromJson-style models. Shape checks, typed exceptions with cause and trace, full-traversal list decoding with aggregated failures, redacted-by-default payloads.

example/json_shield_example.dart

// dart run example/json_shield_example.dart
import 'package:json_shield/json_shield.dart';

// A quicktype-style model, used unmodified.
class User {
  final String name;
  final int age;
  const User({required this.name, required this.age});

  factory User.fromJson(Map<String, dynamic> json) => User(
        name: json['name'] as String,
        age: json['age'] as int,
      );
}

void main() {
  guard.verbose = true; // attach raw payloads while developing

  // 1. Single object.
  final user = guard.decode(
    User.fromJson,
    {'name': 'Ada', 'age': 36},
    context: 'users_me_get',
  );
  print('decoded: ${user.name}');

  // 2. Broken contract: `name` is an int -> DecodeException with the
  //    endpoint label, expectation, raw payload, TypeError cause and trace.
  try {
    guard.decode(User.fromJson, {'name': 123, 'age': 1},
        context: 'users_me_get');
  } on DecodeException catch (e) {
    print(e);
  }

  // 3. List: full traversal, every failure reported at once.
  try {
    guard.decodeList(
      User.fromJson,
      [
        {'name': 'a', 'age': 1},
        'garbage',
        {'name': 'b', 'age': 'NaN'},
      ],
      context: 'users_list',
    );
  } on DecodeListException catch (e) {
    print(e); // 2/3 failed. #1: ...; #2: ...
    for (final f in e.errors) {
      print('  index ${f.index}: ${f.error.cause}');
    }
  }
}