サンプル

Handle Express res.format content negotiation 406 error dispatch, canonicalized err.types, unconditional Vary header, and default fallback semantics

sha256:2fa6c10475b5b6d8e09997cd54b5033b0d036a8e8a20dff8820063ebce125ae2

ケース

ゴール

Handle Express res.format content negotiation 406 error dispatch, canonicalized err.types, unconditional Vary header, and default fallback semantics HOW

パッケージ

express 4.21.2

環境

node

作成日

2026-08-17T06:38:16Z

よくある思い込み

res.format directly renders an HTTP 406 response rather than routing a NotAcceptableError to next(), err.types preserves raw format keys like ['html'], and default handlers receive a pre-assigned Content-Type.

このサンプルの作者が、ここで開発者やモデルが期待するであろうこととして記録したもの。下の契約が実際に実行されたものだ。

コントラクト

• res.format routes an HTTP 406 NotAcceptableError to next() with canonicalized MIME types in err.types and unconditionally sets Vary: Accept when no registered format matches the Accept header and no default handler is provided
• res.format sets the Content-Type header to the canonical MIME type of the matched format key before executing the handler callback
• res.format wildcard matching with Accept: */* selects the first format key defined on the object and applies its canonical Content-Type
• res.format executes the default fallback handler without pre-setting Content-Type while preserving the Vary: Accept header
• res.format with an empty object forwards an HTTP 406 NotAcceptableError with an empty err.types array to next()

ファイル

• NOTES.md
• csx.json
• package-lock.json
• package.json
• test/contract.mjs

ソースアーティファクトをダウンロード (tar.gz)

オリジンシーダー

csx-seed

検証レシート

• node 22 · linux alpine/x64 · docker · CONTAINER_RUN · compile:SKIPPED · contract:PASS · load:PASS · resolve:PASS · node-typescript@1 · 2026-08-17 · ed25519:d91480838ac982c9