cache-client-headers-explained.md

title	Client cache headers explained / Expired vs Pragma vs Cache-Control
layout	default

/ nginx / docs

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Client cache headers explained / Expired vs Pragma vs Cache-Control

Client cache is being considered the client's brower's cache that stores files like CSS, Javascript based on 'Etag' header received from the server.

Resources

• https://www.sitepoint.com/solve-caching-conundrums/

Expired t

IMO works like shorthand for 'Cache-control: public max-age=t'.

Pragma

• Difference between pragma and cache-control

Pragma public is same as Cache-Control: public just for IE older browsers. Pragma is the HTTP/1.0 implementation and cache-control is the HTTP/1.1 implementation of the same concept.

Pragma / Cache-control values

private

Indicates that the response is intended for a single user and must not be stored by a shared cache. A private cache may store the response.

no-cache

Forces caches to submit the request to the origin server for validation before releasing a cached copy. only-if-cached Indicates to not retrieve new data. The client only wishes to obtain a cached response, and should not contact the origin-server to see if a newer copy exists.

must-revalidate

The cache must verify the status of the stale resources before using it and expired ones should not be used.

proxy-revalidate

Same as must-revalidate, but it only applies to shared caches (e.g., proxies) and is ignored by a private cache.