CODEWITHSUNDEEP
iis-7
Chris Fewtrell
Chris Fewtrell

Reputation: 7715

Output caching still adding Cache-Control:no-cache even when it is disabled

Background

A customer is running our web app. over HTTPS and are running into the (fairly well know) IE8 "file cannot be written to cache" error when they try to view a PDF/Excel/word file because the response contains the HTTP Cache-Control:no-cache directive. The thing is, it is not our app (or its config) that is adding this directive.

After a bit of investigating I discovered that the IIS7 page output caching feature can also add this header, for example 

<caching enabled="false" enableKernelCache="false">
    <profiles>
        <add extension=".htm" policy="CacheUntilChange" kernelCachePolicy="CacheUntilChange" />
    </profiles> 
</caching>

will have the effect of adding Cache-Control:no-cache, private to response headers.

My Question

But the surprising (IMO) thing is that even when you supposedly disable the feature (see in my config snippet above that enabled="false"), the response headers are still being sent with Cache-Control:no-cache, private.

Am I being stupid to be surprised by this (I guess I probably am)?

Upvotes: 10

Views: 7111

Answers (4)

Todd Menier
Todd Menier

Reputation: 39289

What effectively got rid of no-cache for me was adding location="Any" to the add element, which instead writes Cache-Control:public:

<caching enabled="false" enableKernelCache="false">
    <profiles>
        <add extension=".htm" ... location="Any" />
    </profiles> 
</caching>

In the absence of the location attribute, IIS defaults to Cache-Control:no-cache. Other possible values are Client, Downstream, Server, or ServerAndClient. Details here.

Upvotes: 8

BornToCode
BornToCode

Reputation: 10213

Try to add this to your web.config, it completely removed the Cache-Control header for me:

<system.Webserver>
<staticContent>
<clientCache cacheControlMode="NoControl" />
</staticContent>
</system.Webserver>

Upvotes: 0

James Hay
James Hay

Reputation: 12700

Remove the '.' within the extension attribute:

<profiles>
    <add extension="htm" policy="CacheUntilChange" kernelCachePolicy="CacheUntilChange" />
</profiles>

Upvotes: 4

jColeson
jColeson

Reputation: 971

You're not alone: http://forums.iis.net/t/1152306.aspx

We also had the same problem. I haven't found any documentation about this "feature" so I'm assuming it is a bug.

We decided to just remove the caching tag and use only the clientCache tag instead.

Upvotes: 5

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