if (!path.StartsWith (app_virtual_dir))
throw new ArgumentNullException ("path is not rooted in the virtual directory");
string rest = path.Substring (app_virtual_dir.Length);
if (rest.Length > 0 && rest [0] == '/')
rest = rest.Substring (1);
if (!path.StartsWith (app_virtual_dir))
throw new ArgumentNullException ("path is not rooted in the virtual directory");
string rest = path.Substring (app_virtual_dir.Length);
if (rest.Length > 0 && rest [0] == '/')
rest = rest.Substring (1);