Why aren't my images caching?

问题

I have an ASP.NET MVC3 application setup. There is a controller that returns back images and I have added the following:

[OutputCache(Duration = 3600, VaryByParam = "id;width", Order = 1000, Location = OutputCacheLocation.Client)]
public ActionResult Get(string id, int width)
{ ... }

But when I check out the HTTP Response on these images they all have headers that say "cache-control: no-cache" and "expires: -1" which means the browser is never caching them.

I'm looking all around and I can't find anything on why the response is telling the browser not to cache them. I even tried working up my own attribute that did:

public class ContentExpiresHeader : ActionFilterAttribute
{
    public override void OnResultExecuted(ResultExecutedContext filterContext)
    {
        var cache = filterContext.HttpContext.Response.Cache;
        cache.SetExpires(DateTime.Now.AddYears(1));
        cache.SetCacheability(HttpCacheability.Private);
        cache.SetLastModifiedFromFileDependencies();
        base.OnResultExecuted(filterContext);
    }
}

but that didn't get me anywhere either.

Any help is appreciated.

UPDATE: I'm starting to think this has got to be an IIS setting somewhere that is adding the no-cache and overriding. I can't seem to find anything, though. The only odd thing is that if I take a look at the state of the cache variable after I've called the .Set...() methods the internal variables have not been updated. I would have expected something to change but they're still showing "no-cache".

UPDATE 2: I should add that the return of this method is a:

return File(...);

UPDATE 3: I also found this (http://dotnetslackers.com/articles/aspnet/ASP-NET-MVC-3-Controller-for-Serving-Images.aspx) and tried implementing it without any luck. Still getting the no-cache options on the response header for the images.

UPDATE 4: Just had to check server settings... if I bypass my controller and go straight to an image file on the server, then it DOES cache and has the correct caching settings in the response header.

UPDATE 5 (yeah, getting crazy): Created a brand new MVC3 project and just made the one controller and it cached just fine. So I've got something outside the immediate code that is adding this pragma:no-cache stuff and for the life of me I can't figure out what it'd be. =-/

回答1:

Try changing the cacheability from HttpCachability.Private to HttpCachability.ServerAndPrivate. It should keep the cache-control as private and not suppress e-tags/last modified.

回答2:

Found the problem! And it's the weirdest thing I've seen in a while.

I am using SocialAuth-net and somewhere during the setup I added the system.webServer module for it and set runAllManagedModulesForAllRequests=true. I thought, "huh, wonder if that's causing it somehow", as I couldn't reproduce the problem outside this particular app. Low and behold, commenting out that section of the config and my images started caching! Hoorah!

But, it gets weirder. I undid my config changes, refreshed and now I'm still getting caching. I can't tell you how many resets of the system I've done with no change but somehow temporarily removing these modules from the pipeline seems to have resolved this problem.

I can track it down to the SocialAuthHttpModule and if I remove it SocialAuth-net still seems to work but caching is restored reliably. Very weird.

来源：https://stackoverflow.com/questions/11463733/why-arent-my-images-caching