fix(cors): expose Retry-After so browser JS can honor 429 back-off (#322)#323
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express-rate-limit (standardHeaders: true) sets `Retry-After` on
the 429 response — the integer-seconds the client should wait
before retrying (RFC 7231 §7.1.3). Browser JS reading the
response across CORS can't see headers outside the CORS-safelisted
set unless the server explicitly exposes them via
`Access-Control-Expose-Headers`.
`Retry-After` is NOT on the CORS safelist (only Cache-Control,
Content-Language, Content-Length, Content-Type, Expires,
Last-Modified, Pragma are), so a browser-side `fetch()` getting
a 429 reads `headers.get('Retry-After')` as null and falls back
to a fixed-delay retry instead of honoring the server's
back-off. Add it to the existing exposedHeaders list alongside
the other RateLimit-* headers.
Update tests:
- cors-expose-headers.test.js mirrors the new entry.
- rate-limit.test.js asserts the 429 response actually carries
`Retry-After` as a positive-integer string (defensive — the
server-side path could change without the CORS list catching
it).
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
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Closes #322.
Summary
Adds
'Retry-After'to server.jsexposedHeadersand mirrors the entry in the CORS expose-headers test. Adds an assertion in the rate-limit test that the 429 response actually carries the header (positive-integer-seconds per RFC 7231 §7.1.3).Without this, browser JS reading a cross-origin 429 sees
Retry-Afteras null and can't honor the server's back-off.Test plan
npm run lint && npm test— 782 passing (1 new assertion added to existing 429 test rather than a new test block).Proudly Made in Nebraska. Go Big Red! 🌽 https://xkcd.com/2347/