Sample
express 4.21.0: Negotiate response content types with res.format, automatic Vary and Content-Type header injection, wildcard fallback, and 406 Not Acceptable error delegation
Verified sample for npm express 4.21.0: Negotiate response content types with res.format, automatic Vary and Content-Type header injection, wildcard fallback…
sha256:2752bf7c02fd809432943b420ccc39a51bafb6c2fadccf23663bfaac4281c1d9
This network offers one thing: a sample that builds. It ran the sample in a sandbox and kept the signed receipt. It grades nothing and warrants nothing — whether the same code builds where you are is not something it measured.
How many distinct signing keys filed a passing contract receipt. One is the author alone; more than one means somebody else built it too. A key is self-generated with nothing registered behind it, so it counts keys, not people.
MIT-0
Execution evidence
The declared environment and the signed runs are kept apart, so you can see exactly what this sample ran and where.
- Evidence basis
- Signed contract pass
- Verification receipts
- 2
- Signing keys that built it
- 2
Declared environment
node linux x64 node node npm
Verification-run environments
| Environment | Contract | Stages | Run |
|---|---|---|---|
| node 22 · linux alpine/x64 · docker ed25519:d91480838ac982c9 | PASS | compile:SKIPPED · contract:PASS · load:PASS · resolve:PASS CONTAINER_RUN · node-typescript@1 |
2026-08-17 |
| node 22 · linux alpine/x64 · docker ed25519:2175b912ea1c23b1 | PASS | compile:SKIPPED · contract:PASS · load:PASS · resolve:PASS CONTAINER_RUN · node-typescript@1 |
2026-08-18 |
Case
HOW- Goal
- Negotiate response content types with res.format, automatic Vary and Content-Type header injection, wildcard fallback, and 406 Not Acceptable error delegation
- Packages
- Symbols
-
- express
- res.format
- Environment
- node
- Created
- 2026-08-17T06:38:47Z
Contract
- res.format automatically sets the Vary: Accept header and pre-populates Content-Type matching the negotiated format before executing the handler
- res.format with wildcard Accept */* selects the first property key enumerated in the format object
- res.format negotiates formats by request Accept q-factor weights regardless of object key definition order
- res.format without a matching format or default property forwards an HTTP 406 Not Acceptable Error with err.types to next()
- res.format translates extension shortcuts like text and json into canonical MIME types in err.types
- res.format executes the default callback property when no format matches the Accept header without triggering a 406 error
Files
- NOTES.md
- csx.json
- package-lock.json
- package.json
- test/contract.mjs