c# - How to undo Response.Cache.SetNoStore()?

Question

I've a CMS application code which calls Response.Cache.SetNoStore() on all request and if i'm correct, this will be prevents proxies/cdn to cache those pages/content. Therefore, i'm conditionally calling the below code:

Response.Cache.SetCacheability(HttpCacheability.Public);
Response.Cache.SetMaxAge(new TimeSpan(0, 30, 0));
Response.Cache.SetValidUntilExpires(true);

But this doesn't take out the no-store param from the response header, this is the returned http header:

Cache-Control:public, no-store, must-revalidate, max-age=1800

Therefore my question is, how can i take out the nostore param pragmatically? If this isn't possible, how/where can i parse/modify the http-header, because i tried to parsed on PagePreRender event and the nostore param hasn't been applied...which leads to wonder at which life cycle is this appended to the header?

Answer 1

There is a way to undo SetNoStore once you call it. You need to use some creative routing to process the request in a different way or reflection to invoke the built-in reset that is private.

You can get access to HttpCachePolicyWrapper to access the underlying HttpCachePolicy, then assign the internal NoStore field or issue Reset to revert to the default cache policy.

response.Cache.SetNoStore(); // assign no-store
BindingFlags hiddenItems = BindingFlags.NonPublic | BindingFlags.Instance;
var httpCachePolicyWrapper = response.Cache.GetType(); // HttpCachePolicyWrapper type

var httpCache = httpCachePolicyWrapper.InvokeMember("_httpCachePolicy", BindingFlags.GetField | hiddenItems, null, response.Cache, null);
var httpCachePolicy = httpCache.GetType(); // HttpCachePolicy type

// Reset Cache Policy to Default    
httpCachePolicy.InvokeMember("Reset", BindingFlags.InvokeMethod | hiddenItems, null, httpCache, null);
var resetAllCachePolicy = httpCachePolicy.InvokeMember("_noStore", BindingFlags.GetField | hiddenItems, null, httpCache, null);

response.Cache.SetNoStore(); // assign no-store

// Undo SetNoStore Cache Policy
httpCachePolicy.InvokeMember("_noStore", BindingFlags.SetField | hiddenItems, null, httpCache, new object[] { false });
var resetNoStoreOnly = httpCachePolicy.InvokeMember("_noStore", BindingFlags.GetField | hiddenItems, null, httpCache, null);