BCP56bis: more Cache-Control directive practice

[Jxck]

Cache-Control header seems a one of confusing point for developer.

for example, as @mnot noted in Cache-Control in the wild | Fastly there are a lot of strange directive combination which says much developer doesn't understand Cache-Control correctly.

So I hope BCP include more important practice around caching.

private / public

mentioning about adding private for private content which must not be stored in shared cache.
and public is not a thing for public content because caches are public by default.

explicit cache-control for heuristic cache

no Cache-Control header doesn't mean un-cacheable. browser could cache them under heuristic caching theory.
so if you have any restriction around caching, adding cache-control header for explicit control.

see also Twitter Direct Message Caching and Firefox - Mozilla Hacks - the Web developer blog

no-cache is not a "don't cache"

already mentioned is draft

max-age=0 + must-revalidate

it's better to use no-cache (almost same bihavior)

Cache-Control: max-age=0, must-revalidate # 👎
Cache-Control: no-store # 👍

s-maxage & proxy-revalidate

s-maxage & proxy-revalidate are optional when you do different control for shared proxy. so
if max-age and s-maxage has same value, s-maxage is ommitable.
if must-revalidate is present, proxy-revalidate is ommitable.

Cache-Control: max-age=100, s-maxage=100, must-revalidate, proxy-revaliate 👎
Cache-Control: max-age=100, must-revalidate 👍

throw the kitchen sink

if you really wanna make this not cacheable and avoid store any cache, best choice is to use no-store alone.

Cache-Control: no-cache, no-store, must-revalidate, proxy-revalidate, max-age=0 # 👎
Cache-Control: no-store # 👍

throw the kitchen sink is almost meaningless and not only waste bytes but also implementation could cause a problem because no-store and other directives are semantically conflicted.

reload request (max-age=0 or no-cache)

semantically, no-cache should works fine when you do like Reloading of browser.
(but I don't know why browser sends max-age=0 when reloading instead of no-cache.
if there are some reason/use-case for max-age=0 it could be noted here too)

I'll update if I remember more ideas. Correct me if I also misunderstood.
Thanks

[mnot]

I think most of these are now addressed in the text. I didn't attempt some as they seem too detailed / situational (the spec is already pretty long!).

Thanks,