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两部分问题（部分密切相关）：使用 IIS7 采用的默认 OOTB ETag 策略，为什么我们在浏览页面时看不到 If-None-Match/304 交互？

例如，为空缓存请求返回的标头是：

Content-Type    image/png
Last-Modified   Thu, 03 Dec 2009 15:51:56 GMT
Accept-Ranges   bytes
Etag    "a8a0628a3074ca1:0"
Server  Microsoft-IIS/7.0
X-Powered-By    ASP.NET
Date    Tue, 22 Dec 2009 19:47:36 GMT
Content-Length  1780

...但随后对该页面的访问不会为图像生成 304 往返？

此外，IIS7 的默认applicationHost文件具有以下 (1)：

   <caching enabled="true" enableKernelCache="true">
   </caching>

enableKernelCache='true'是否扩展到所有静态文件，使您无需显式注册扩展以授予CacheUntilChange作为内核策略 (2)：

<caching>
  <profiles>
    <add extension=".gif" policy="DontCache" kernelCachePolicy="CacheUntilChange" duration="0.00:01:00" location="Any" />
    <add extension=".png" policy="DontCache" kernelCachePolicy="CacheUntilChange" duration="0.00:01:00" location="Any" />
    <add extension=".js" policy="DontCache" kernelCachePolicy="CacheUntilChange" duration="0.00:01:00" location="Any" />
    <add extension=".css" policy="DontCache" kernelCachePolicy="CacheUntilChange" duration="0.00:01:00" location="Any" />
    <add extension=".jpg" policy="DontCache" kernelCachePolicy="CacheUntilChange" duration="0.00:01:00" location="Any" />
    <add extension=".jpeg" policy="DontCache" kernelCachePolicy="CacheUntilChange" duration="0.00:01:00" location="Any" />
  </profiles>
</caching>

(1) %systemroot%\System32\inetsrv\config\applicationHost.config

(2) http://labs.episerver.com/en/Blogs/Per/Archive/2009/3/Configuring-cache-expiration-on-IIS-7/

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1 回答 1

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The handling of ETags and the associated If-None-Match / If-Modified-Since is somewhat browser dependent. You might try a few different browsers and see what happens -- in general, if you don't set an explicit expiration time, I would expect to see the 304's, as you said.

For kernel caching, it is enabled for static files by default. To help see what's happening, I've found it helpful to run the following command:

netsh http show cachestate

That will show information about the files that are currently in the cache.

Keep in mind that files normally have to be referenced a couple of times within a certain time window before the kernel will cache them.

于 2009-12-22T20:41:42.673 回答