Is there a way to verify that Response.Cookies.Add() succeeded? - asp.net

Question

In ASP.net 2.0 Response.Cookies.Add() is a VOID (which boggles me somewhat). Is there a way to check to see if the function successfully added the cookie?
I just spent 2 hours trying to track down an authentication issue for one user. Finally I realized he was in a BUNCH of AD groups and I believe the cookie we were building for him, and trying to set, was > 4096 bytes.
Would be nice to know up front if the call to Response.Cookies.Add() failed.
We were trapping the error later in the global.asax page when we did:
HttpCookie authCookie = Context.Request.Cookies[cookieName];
and authCookie for this user was always null.
Thanks for the responses.
I've decide to check the size before calling Response.Cookies.Add() and alert the user accordingly.
int iSize = System.Text.UTF8Encoding.UTF8.GetByteCount(authCookie.Values.ToString());
if (iSize > 4096)
{
lblMessage.Text = "The authentication cookie cannot be set as it is > 4096 bytes; a limit imposed by the browser. The current size of the Cookie.Values is " + iSize.ToString() + " bytes.";
lblMessage.CssClass = "msgBox Alert";
return;
}

Answer 1

I setup a simple project that write a random cookie value, and used Fiddler to examine the response:
GET http://localhost.:2605/Default.aspx HTTP/1.1
Accept: */*
Accept-Language: en-us
User-Agent: Mozilla/4.0 (compatible; MSIE 7.0; Windows NT 5.1; Trident/4.0; .NET CLR 1.1.4322; .NET CLR 2.0.50727; .NET CLR 3.0.4506.2152; .NET CLR 3.5.30729; .NET4.0C; .NET4.0E)
Accept-Encoding: gzip, deflate
Connection: Keep-Alive
Host: localhost.:2605
Pragma: no-cache
Cookie: ASP.NET_SessionId=wxpo32z2zxr1qlbwgx4on3z2; test1047139665=value775124204
You can see the cookie in the Cookie section of the header above. This is consistent with the documentation at: http://msdn.microsoft.com/en-us/library/system.web.httpresponse.cookies.aspx
The size limitation is documented here:
http://support.microsoft.com/kb/306070
Looks like you'll have to check yourself before writing it.

Answer 2

Yes, but likely not how you want to. On the subsequent page or request, check it in Request.Cookies if the cookie is available. If not, you can assume the Response.Cookies wasn't able to add the cookie (they have cookies off, cleared them, etc.).
You can't verify the Response.Add worked when it happens because it doesn't truly happen until the response is sent to the browser.

Answer 3

Response.Cookie.Add() succeeds always. It's the client accepting said cookie that might fail. But the Add() method has no way of knowing - since it just places the cookie in the HTTP response. You won't know until the HTTP response is sent back and the client processes it. Which happens long after Add() returns.
So the only way to verify that is to check for the cookie on subsequent requests, which seems like you're already doing by checking for the auth info.