Why use Cache-control headers in request?

The local cache is also part of the cache proxy.

Use Cache-control to represent cached usage policies when requested.

The No-cache in the request header indicates that the browser does not want to read the cache, not the cache. Generally in the browser press Ctrl+f5 Force Refresh, the request head has this no-cache, that is, skip the strong cache and negotiate cache phase, directly request the server. (If you press F5 directly, the request header is max-age=0, only the strong cache is skipped, but the cache is negotiated)
And the response head max-age=259200, not very clear, not verified.

http://bbs.csdn.net/topics/391022213

There may is any number of intermediate proxies between the client and server which do caching. The client can explicitly request explicit caching behaviour from any and all caching entities, things like:

• max-age-"I don ' t want a response older than X"
• no-cache-"I want a fresh response"
• no-transform-"I don t want it unless it ' s the original"
• only-if-cached-"Don ' t bother the origin server if you Don ' t have it already"

As with all requests, servers has a certain leeway in whether to honour the request or not. Just because a client insists on an uncached response doesn ' t mean it's necessarily going to get it.

Https://stackoverflow.com/questions/42652931/why-use-cache-control-header-in-request

Cache-Control: no-cacheis generally used in a request header (sent from web browser to server) to force validation of the resource in the Interme Diate proxies. If the client doesn ' t send this request to the server, intermediate proxies would return a copy of the content if it is fre SH (have not expired according to Expire or fields max-age ). Cache-Control directs these proxies to revalidate the copy even if it is Fresh.

Https://stackoverflow.com/questions/14541077/why-is-cache-control-attribute-sent-in-request-header-client-to-server

Why use Cache-control headers in request?