apache - ExpiresActive On .htaccess 解释

Question

[i]ExpiresActive On
ExpiresByType image/gif A2592000
ExpiresByType image/jpeg A2592000
ExpiresByType image/png A2592000
BrowserMatch "MSIE" brokenvary=1
BrowserMatch "Mozilla/4.[0-9]{2}" brokenvary=1
BrowserMatch "Opera" !brokenvary
SetEnvIf brokenvary 1 force-no-vary[/i]

最近在示例 .htaccess 中看到了此代码。

大概 ExpiresByType 设置图像的到期时间 - 这与访问者浏览器缓存有关吗？什么是 A2592000 翻译成？

“brokenvary=1”是什么意思？我收集它正在寻找一个 UserAgent，但是然后呢？

谢谢!

Answer 1

Presumably ExpiresByType sets an expiry time on images - is that related to the visitors browser cache?

是的。 mod_expires允许根据类型轻松设置过期规则。

但是过期时间只指定了某个响应的新鲜时间。这并不一定意味着 response is cacheable .但是in general, any successful response is cacheable unless there are restrictions :

Unless specifically constrained by a cache-control (section 14.9) directive, a caching system MAY always store a successful response (see section 13.8) as a cache entry, MAY return it without validation if it is fresh, and MAY return it after successful validation.

因此，除非您指定根本不存储响应(即使用 no-store )，否则响应可能由公共(public)缓存(共享缓存)和私有(private)缓存(本地缓存)存储。

And what does A2592000 translate to?

响应的新鲜时间可以使用绝对时间值(例如“2010-10-09”)或相对时间值(例如“明天”)来表示。日期格式A2592000使用后一个时间值作为 A表示访问时间，2592000是添加的秒数。所以A2592000表示“从访问时间开始 2592000 秒”。

And what does the "brokenvary=1" imply? I gather it's looking for a UserAgent, but then what?

Apache 有一些 special purpose environment variables在哪里 force-no-vary 是其中之一:

This causes any Vary fields to be removed from the response header before it is sent back to the client. Some clients don't interpret this field correctly; setting this variable can work around this problem. Setting this variable also implies force-response-1.0.

现在Vary header field用于指定 list of header field names the server used to select the response among multiple representations :

A server SHOULD use the Vary header field to inform a cache of what request-header fields were used to select among multiple representations of a cacheable response subject to server-driven negotiation.

因此，如果您使用内容协商和请求的通用 URL，如 /document.html被请求并且该资源有多种表示形式(例如，英语和德语)并且您的服务器选择德语变体，因为 Accept-Language 声明值 de ，服务器将包含一个 Vary 字段，其中包含 Accept-Language让缓存知道选择是基于 Accept-Language 的值。

但是一些用户代理没有做到这一点。在这种情况下，不应该发送 Vary 头字段，这可以通过设置专用环境变量 force-no-vary 来完成。 .