Using Undici cache, what max-age is the response supposed to have?

[steunix]

Hi all,

I'm trying to use Undici cache in a NodeJS frontend, but I'm not sure about what my backend API should set max-age to.
I setup the cache in the frontend with

import * as UNDICI from 'undici'
const CACHE = new UNDICI.cacheStores.MemoryCacheStore({
  maxSize: 100 * 1024 * 1024,
  maxCount: 1000,
  maxEntrySize: 5 * 1024 * 1024
})

UNDICI.setGlobalDispatcher(UNDICI.getGlobalDispatcher().compose(
  UNDICI.interceptors.cache({
    store: CACHE,
    methods: ['GET', 'HEAD']
  })
))

With max-age=0 is in the response, upon UNDICI.request the client always sends these headers, without if-none-match or if-modified-since:

accept-encoding = gzip, deflate, br
authorization = Bearer <omitted>
connection = keep-alive
host =localhost:3000
user-agent = passweaver-gui

the server return these headers:

cache-control = public, max-age=0
connection = keep-alive
content-length = 55
content-type = application/json; charset=utf-8
date = Sun, 12 Oct 2025 13:43:47 GMT
etag = W/"37-bHgTKCgPX/sEMxUJysWJC2T9rWo"
keep-alive = timeout=5
vary = Authorization, Accept-Encoding, Accept-Language

Repeated requests then always return 200.

If I change max-age to 1 in the response, the requests contains if-none-match and if-modified-since:

accept-encoding = gzip, deflate, br
accept-language = 
authorization = Bearer <omitted>
connection = keep-alive
host = localhost:3000
if-modified-since = Sun, 12 Oct 2025 13:48:41 GMT
if-none-match = W/"37-bHgTKCgPX/sEMxUJysWJC2T9rWo"
user-agent = 'passweaver-gui'

Thus subsequent requests return 304

Shouldn't cache work with max-age=0 too, and possibily with no-cache? Am I missing something in the backend response header?

Just to be clear, I would like EVERY request to be checked with if-none-match, and for this reason I am using max-age=0

I'm using NodeJS v22.20.0 and Undici v7.16.0

[metcoder95]

I believe this must be a bug; if max-age is set to 0, cache must immediately revalidate the cached response in further request. In combination, with the if-none-match, the server must reply with 304 if the cache hasn't been modified.

Would you like to send a PR to address that?

[steunix]

From what I can see debugging, the problem may be in determineStaleAt function (called inside onResponseStart) in cache-handler.js: in case of max-age = 0 (pos 339) it returns undefined while it should returns 0 (stales now).

Also in case of "no-cache" header that function should return 0, if I correctly get the function purpose.

Or am I missing some bigger picture?

[metcoder95]

That's a good start, feel free to open a PR for and we can take it from there

[steunix]

Done: #4623

Thanks!