Sample
express 4.21.2: Handle Express res.format content negotiation 406 error dispatch, canonicalized err.types, unconditional Vary header, and default fallback semantics
Verified sample for npm express 4.21.2: Handle Express res.format content negotiation 406 error dispatch, canonicalized err.types, unconditional Vary header…
sha256:2fa6c10475b5b6d8e09997cd54b5033b0d036a8e8a20dff8820063ebce125ae2
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
- Handle Express res.format content negotiation 406 error dispatch, canonicalized err.types, unconditional Vary header, and default fallback semantics
- Packages
- Symbols
-
- res.format
- Environment
- node
- Created
- 2026-08-17T06:38:16Z
Contract
- 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()
Files
- NOTES.md
- csx.json
- package-lock.json
- package.json
- test/contract.mjs