サンプル

Write fromJson and toJson by hand in Dart with dart:convert and json_annotation, with no build_runner and no generated file, and find out where an unchecked payload actually fails

sha256:aa7e5100c4783c97efd691bb409fe9cad0feebfb84875a777d81fdc86f5f8fe0

ケース

ゴール

Write fromJson and toJson by hand in Dart with dart:convert and json_annotation, with no build_runner and no generated file, and find out where an unchecked payload actually fails HOW

パッケージ

json_annotation 4.12.0

環境

dart 3

作成日

2026-08-14T20:06:25Z

コントラクト

• assert a payload whose every field has the wrong type still decodes, that reading a field out of it still succeeds because both are typed dynamic, and that the first failure is a TypeError at the first typed use in code that never mentions JSON, with reviver the only hook that runs during the decode itself
• assert a decoded array is List<dynamic> and is not a List<String> even when every element is a String, and that the usual .cast<String>() fix defers again into a lazy view whose construction and length succeed with a bad element inside while reading that element throws, where List<String>.from fails at the decode
• assert a JSON number is int or double according to how it was spelled, so as int rejects 3.0 and as double rejects 3, that num survives both at the cost of a silent truncation in toInt, and that an integer literal past the 64-bit range decodes as a double with its low digits already gone
• assert a missing key reads back as null without throwing and is indistinguishable from an explicit null except through containsKey, that it becomes a TypeError in a non-nullable field and silence in a nullable one, and that $checkKeys separates missing, unrecognized and disallowed-null into three named exceptions before any value is read
• assert decoding gives a String and encoding a DateTime throws, that DateTime.parse returns UTC for a numeric offset as well as for a trailing Z so the offset is lost on the way out rather than on the way in, that toIso8601String writes no zone designator at all for a non-UTC value, and that the round trip is not == the original because DateTime's == compares the isUtc flag
• assert jsonEncode resolves toJson by dynamic dispatch with no interface involved, that a class without one throws JsonUnsupportedObjectError caused by NoSuchMethodError, and that a toJson returning an unencodable value re-attributes the error to your class with the real offender only reachable through cause
• assert $checkedCreate and $checkedConvert turn the same TypeError into a CheckedFromJsonException naming the class and the JSON key, including the key rather than the Dart field name and including a key that was missing, while leaving a good payload untouched
• assert @JsonSerializable and @JsonKey change nothing at runtime without the generator, so the declared rename and default value are ignored and the hand-written code is what decides the wire key

ファイル

• csx.json
• lib/product.dart
• probe.dart
• pubspec.lock
• pubspec.yaml
• test/contract_test.dart

検証済みアーティファクトをダウンロード (tar.gz) — 契約が実行された正確なバイト列

オリジンシーダー

anonymous

検証レシート

• dart 3 · CONTAINER_RUN · compile:SKIPPED · contract:PASS · load:PASS · resolve:PASS · pub@1 · 2026-08-14 · ed25519:a2ec939a4c60e243