MVC4 Request headers - asp.net

Question

I have rather bizarre behaviour in my MVC web application.
[AttributeUsage(AttributeTargets.Class | AttributeTargets.Method, Inherited = true, AllowMultiple = true)]
public class NoCacheFilterAttribute : ActionFilterAttribute
{
ctx.Response.AddHeader("Cache-Control", "no-cache);
}
I am adding this filter class to GlobalFilterCollection so that it runs on every action.
I am attempting to override this header selectively in one of my home controller action method.
Response.Headers.Remove("Cache-Control");
Response.AddHeader("Cache-Control", "private,must-revalidate,proxy-revalidate ");
Problem is non these code are setting the correct values. When I inspect the values in response header the Cache-Control is set to "private, s-maxage=0". I scanned all my code to see if I was explicitly doing so anywhere but I don't see myself doing that. The odd thing is If I call
Response.Cache.SetNoStore(); or Any methods of Response.Cache. the response value of Cache-Control then changes. I am not sure why Response.AddHeader or AppendHeader doesn't work?

Answer 1

The "Cache-Control" response header in ASP.NET is special and shouldn't be set explicitly. Instead, use the first-class APIs hanging off of the Response.Cache object as you've already found.

Answer 2

Could you solve it by adding some conditional logic before performing ctx.Response.AddHeader("Cache-Control", "no-cache)?
Basically, you could create another filter named [ApplyCache] to apply to your action method for which you don't want no-cache set, and in NoCacheFilterAttribute, you can do this,
[AttributeUsage(AttributeTargets.Class | AttributeTargets.Method, Inherited = true, AllowMultiple = true)]
public class NoCacheFilterAttribute : ActionFilterAttribute
{
public override void OnActionExecuted(HttpActionExecutedContext ctx)
{
if (!ctx.ControllerContext.ControllerDescriptor.GetFilters().Contains(new ApplyCache()) && !ctx.ActionDescriptor.GetFilters().Contains(new ApplyCache())
{
ctx.Response.Headers.Add("Cache-Control", "no-cache");
}
}
}
For MVC this could be,
public class ApplyCache: System.Web.Mvc.ActionFilterAttribute
{
}
public class NoCache: System.Web.Mvc.ActionFilterAttribute
{
public override void OnActionExecuted(ActionExecutedContext actionExecutedContext)
{
if (!actionExecutedContext.ActionDescriptor.IsDefined(typeof(ApplyCache), true))
{
actionExecutedContext.RequestContext.HttpContext.Response.AddHeader("Cache-Control", "no-cache");
}
}
}
and you want to add both filters to your global collection.
public static void RegisterMvcFilters(GlobalFilterCollection filters)
{
filters.Add(new ApplyCache());
filters.Add(new NoCache());
}

Answer 3

OK. This is what I found out. Any time anywhere in your code if you use (any other NuGet library may be setting the headers) following code:
Response.Cache.SetNoStore(); //or any other .SetXXX; methods
, the headers are written to buffer, and if you issue say following code (some examples using this in ActionFilterAttribute):
HttpContext ctx = HttpContext.Current;
ctx.Response.AppendHeader("Cache-Control", "private, must-revalidate, proxy-revalidate ");
ctx.Response.AddHeader("Cache-Control", "private, must-revalidate, proxy-revalidate ");
ctx.Response.Headers.Set("Cache-Control", "no-cache, no-store, must-revalidate, proxy-revalidate");
to modify the header, the header values are not written. Only way to reset the header is to issue following line of code and then the issue the code above or call Response.Cache.SetXXX methods.
ctx.Response.ClearHeaders();
The Response.Cache does not provide a mechanism to reset the response headers values that were set using .SetXXXX methods. If Response.Cache.SetXXX method was never called then calling Response.AppendHeader, AddHeader or Headers.Set will work without any need to call Response.ClearHeaders();