HTTP Headers

Client hints

Client hints are a set of HTTP request header fields that a server can proactively request from a client to get information about the device, network, user, and user-agent-specific preferences. The server can determine which resources to send, based on the information that the client chooses to provide.
客户端提示是一组 HTTP 请求标头字段，服务器可以主动向客户端请求这些字段，以获取有关设备、网络、用户和用户代理特定首选项的信息。服务器可以根据客户端选择提供的信息来确定要发送哪些资源

The Cache-Control HTTP header field holds directives (instructions) — in both requests and responses — that control caching in browsers and shared caches (e.g. Proxies, CDNs).
Cache-Control HTTP 标头字段在请求和响应中保存指令（指令），用于控制浏览器和共享缓存（例如代理、CDN）中的缓存。

HTTP 缓存

Cache-Control

Cache-Control - HTTP | MDN

Request	Response
`max-age`	`max-age`
`max-stale`	-
`min-fresh`	-
-	`s-maxage`
`no-cache`	`no-cache`
`no-store`	`no-store`
`no-transform`	`no-transform`
`only-if-cached`	-
-	`must-revalidate`
-	`proxy-revalidate`
-	`must-understand`
-	`private`
-	`public`
-	`immutable`
-	`stale-while-revalidate`
`stale-if-error`	`stale-if-error`

directives

max-age

The max-age=N response directive indicates that the response remains fresh until N seconds after the response is generated.
max-age=N 响应指令指示响应在生成响应后 N 秒内保持新鲜状态。

Note that max-age is not the elapsed time since the response was received; it is the elapsed time since the response was generated on the origin server. So if the other cache (s) — on the network route taken by the response — store the response for 100 seconds (indicated using the Age response header field), the browser cache would deduct 100 seconds from its freshness lifetime.
请注意， max-age 不是自收到响应以来经过的时间；它是自源服务器上生成响应以来所经过的时间。因此，如果响应所采用的网络路由上的其他缓存将响应存储 100 秒（使用 Age 响应标头字段表示），则浏览器缓存将从其新鲜度中扣除 100 秒寿命。

Cache-Control: max-age=604800
Age: 100

s-maxage

s-maxage 响应指令指示响应在共享缓存中保持新鲜状态的时间。私有缓存会忽略 s-maxage 指令，并覆盖由 max-age 指令或共享缓存的 Expires 标头（如果存在）指定的值。