📅 最后修改于: 2021-01-03 03:09:39 🧑 作者: Mango
HTTP用于分布式操作系统，在其中使用响应缓存，我们可以提高性能。 HTTP / 1.1协议包含许多元素，这些元素旨在使缓存正常工作。因为这些元素相互交互，并且它们是协议其他方面不可分割的，所以将HTTP缓存设计与响应代码，方法，标头等的详细描述分开描述是很有用的。
在许多情况下，HTTP缓存基本上用于消除发送请求的需要。在许多其他情况下，它也用于消除发送完整响应的需要。
在HTTP中，缓存机制是指向缓存的隐式指令，在该缓存中，到期时间和验证器由服务器指定。为此，我们使用Cache-Control标头。
Cache-Control标头用于允许客户端或服务器在请求或响应中传输各种指令。这些指令将覆盖默认的缓存算法。缓存的指令在逗号分隔的列表中指定。
Cache-control: no-cache
客户端在其HTTP请求中使用缓存请求指令，如下所示：
| S.N. | Directive of Cache Request and Description |
|---|---|
| 1 | no-cache It indicates that the response which is returned and cannot be used to satisfy a subsequent request to the same URL. |
| 2 | no-store It indicates that the client will not store anything about the request of the client or the response of the server. |
| 3 | max-age = seconds It is used to indicate that the client is willing to accept a response whose age is not greater than the time which is specified in seconds. |
| 4 | max-state [=seconds ] It is used to indicate that the client is willing to accept a response that has exceeded its expiration time. It must not be expired by more than that time, if the seconds are given. |
| 5 | min-fresh= seconds It is used to indicate that the client is willing to accept a response whose lifetime of freshness is not less than its current age plus, which is the specified time in seconds. |
| 6 | no-transform It does not convert the entity-body. |
| 7 | only-if-cached It does not retrieve new data. A document can be send by the cache only if it is in the cache and should not contact the origin-server to see if it exists a newer copy. |
服务器可以在其HTTP响应中使用高速缓存响应的指令，如下所示：
| S.N. | Directive of Cache Response and Description |
|---|---|
| 1 | public It indicates that any cache may be cached the response. |
| 2 | private It is used to indicate that some part of the response message or all the response message is intended for a single user. It must not be cached by a shared cache. |
| 3 | no-cache It indicates that the response which is returned cannot be used to satisfy a subsequent request to the same URL. |
| 4 | no-store It indicates that the client will not store anything about the request of the client or the response of the server. |
| 5 | no-transform It does not convert the entity-body. |
| 6 | must-revalidate It indicates that the cache must verify the stale document’s status before using it, and expired ones should not be used. |
| 7 | proxy-revalidate The proxy-revalidate directives and the must-revalidate directive have the same meaning, except that it does not apply to non-shared user agent caches. |
| 8 | max-age = seconds It is used to indicate that the client is willing to accept a response whose age is not greater than the time which is specified in seconds. |
| 9 | s-maxage = seconds The maximum age specified by the directives overrides the maximum age specified by either the Expires header or the max-age directives. The private cache always ignores the s-manage directives. |