Cache-Control header cannot be set properly in ASP.NET 2.0 – A solution

Do you know that you cannot set Cache-Control: max-age header in
ASP.NET 2.0? No matter how many combinations you try, you will
always end up with “max-age=0” for sure.

I found solution to the SetMaxAge problem in HttpCachePolicy.
Here’s the code of the function in HttpCachePolicy
(decompiled):

public void SetMaxAge(TimeSpan
delta)
{

if (delta < TimeSpan.Zero)

{

throw new ArgumentOutOfRangeException(“delta”);

}

if (HttpCachePolicy.s_oneYear < delta)

{

delta = HttpCachePolicy.s_oneYear;

}

if (!this._isMaxAgeSet || (delta < this._maxAge))

{

this.Dirtied();

this._maxAge = delta;

this._isMaxAgeSet = true;

}
}

Someone is setting maxAge already to 0. So, if I assign a higher
value it does not get set.

I am not sure why the “(delta < this._maxAge)" condition is necessary. If I somehow set a lower maxAge, I can never increase it!

So, I have made an HttpModule which does this:

void context_EndRequest(object
sender, EventArgs e) {
if (HttpContext.Current.Items.Contains(“SetMaxAge”))
{

FieldInfo maxAge =
HttpContext.Current.Response.Cache.GetType().GetField(“_maxAge”,
BindingFlags.Instance | BindingFlags.NonPublic);

maxAge.SetValue(HttpContext.Current.Response.Cache,
(TimeSpan)HttpContext.Current.Items[“SetMaxAge”]);


// SetMaxAge does not
work.
//HttpContext.Current.Response.Cache.SetMaxAge((TimeSpan)HttpContext.Current.Items[“SetMaxAge”]);

HttpContext.Current.Response.Cache.SetCacheability(HttpCacheability.Public);
HttpContext.Current.Response.Cache.SetExpires(DateTime.Now.AddMinutes(5));
HttpContext.Current.Response.Cache.SetRevalidation(HttpCacheRevalidation.AllCaches);
}
}

If someone sets “SetMaxAge” to a Timespan in the Context.Items,
it will get set to the response and the end of the request. This
ensures, no matter who does what with cache object, maxAge will
definitely be set.

Although this is not a Atlas specific problem, it seems to be a
problem in ASP.NET 2.0 itself.

Now I can cache AJAX call responses on the browser and prevent
roundtrips.

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3 thoughts on “Cache-Control header cannot be set properly in ASP.NET 2.0 – A solution”

  2. I am getting a max-age of 9999999 and TWO Cache-Control headers. the max-age of 9,999,999 seconds, or about 115 days, which conflicts with my setting of 365 days in the Expires HTTP header. I am wondering why I am getting TWO Cache-Control headers, and a max-age I didn’t specify.

    HTTP/1.1 200 OK

    Server: Microsoft-IIS/5.0

    Date: Tue, 08 Jan 2008 19:49:41 GMT

    X-Powered-By: ASP.NET

    Cache-Control: public, max-age=9999999

    X-AspNet-Version: 2.0.50727

    Cache-Control: public

    Expires: Wed, 07 Jan 2009 19:49:41 GMT

    Last-Modified: Thu, 28 Jul 2005 22:08:28 GMT

    Content-Type: image/gif

    Content-Length: 2306

    resp.Cache.SetExpires(DateTime.Now.AddSeconds(365 * 24 * 60 * 60)); // Expires in one year.

    // Public – Allows the response to be cached by clients and shared (proxy) caches.

    resp.Cache.SetCacheability(HttpCacheability.Public);

    resp.Cache.SetValidUntilExpires(true);

    FileInfo file = new FileInfo(path);

    resp.Cache.SetLastModified(file.LastWriteTimeUtc);

    David Stevenson

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