We have an IHttpHandler for stylesheets and add a <link/> tag to the page like this:
HtmlGenericControl link = new HtmlGenericControl("link");
link.Attributes.Add("rel", "stylesheet");
link.Attributes.Add("href", "stylesheet.axd?d=" +
HttpServerUtility.UrlTokenEncode(token));
head.Controls.Add(link);
In the stylesheet.axd handler, we UrlTokenDecode the d query string parameter like this:
var token = HttpServerUtility.UrlTokenDecode(Request.QueryString["d"]);
This works most of the time but every now and then we find one of the following two exceptions in our log:
[FormatException: Invalid character in a Base-64 string.]
System.Convert.FromBase64CharArray(Char[] inArray, Int32 offset, Int32 length)
System.Web.HttpServerUtility.UrlTokenDecode(String input)
...
[FormatException: Invalid length for a Base-64 char array.]
System.Convert.FromBase64CharArray(Char[] inArray, Int32 offset, Int32 length)
System.Web.HttpServerUtility.UrlTokenDecode(String input)
System.Web.HttpServerUtilityWrapper.UrlTokenDecode(String input)
...
Any ideas what would cause this phenomenon?
Remarks:
- the resulting URL is < 1500, so below any known URL limits (e.g. IE: 2083)
- seems to be independent of user agent (we have these exceptions for IE6,7,8, FF & Chrome)
- our (unconfirmed) suspicions include AntiVirus products, HTTP proxies, browser addons
- found this remotely related question, but it's about a viewstate issue
