缓存控制机制中max-age和max-stale的区别

Question

我知道这是一个简单的问题，我相信没有人会把它标记为重复问题，因为我已经搜索了整个 SO。所以我的问题是 max-age 和 max-stale 在 Http 的缓存控制机制中有什么区别，我在 here 中读过它，但我觉得它有点复杂，所以如果有人能解释一下这个吗？会有很大帮助

Answer 1

试试这个，它用例子解释

https://msdn.microsoft.com/en-us/library/27w3sx5e(v=vs.110).aspx

Answer 2

来自RFC 7234：

The "max-age" request directive indicates that the client is unwilling to accept a response whose age is greater than the specified number of seconds. Unless the max-stale request directive is also present, the client is not willing to accept a stale response.

...

The "max-stale" request directive indicates that the client is willing to accept a response that has exceeded its freshness lifetime. If max-stale is assigned a value, then the client is willing to accept a response that has exceeded its freshness lifetime by no more than the specified number of seconds.

也就是说，max-age 是最旧的响应，只要 来自源服务器的 Cache-Control 表明它仍然是新鲜的。 max-stale 表示，即使已知响应已过时，只要响应仅过时该秒数，您也会接受它。

根据Serving Stale Responses：

A cache SHOULD generate a Warning header field with the 110 warn-code (see Section 5.5.1) in stale responses.

因此，如果您指定 max-stale 并收到 no-longer-fresh 响应，Warning header 会通知您。