bool VirtualDirectoryExists(string virtualPath, HttpWorkerRequest worker)
{
VirtualPathProvider vpp = HostingEnvironment.VirtualPathProvider;
// TODO: Remove the second condition of the "if" statement (it is only a workaround) involving DefaultVirtualPathProvider as soon as Mono's DefaultVirtualPathProvider.DirectoryExists method works properly (i.e., the indirectly-called HostingEnvironment.MapPath method should not require an HttpContext.Current.Request object to do its work; also see the comment in the ApplicationHost.MapPath method above)
if (vpp != null && !vpp.GetType().FullName.Equals("System.Web.Hosting.DefaultVirtualPathProvider", StringComparison.Ordinal))
return vpp.DirectoryExists (virtualPath);
string physicalPath = (worker != null) ? worker.MapPath (virtualPath) : MapPath (virtualPath);
return Directory.Exists (physicalPath);
}