determine if file is loaded directly via URL

As opposed to, say, via <script> or <link> tags (or @include'd). Is there any way in node.js to tell the difference between a file/resource being loaded via direct URL and via another page?

I am using http.createServer, although if another module can provide this information I'd like to know. Also, I want to know if I can achieve this without modifying the URL (like adding ?flag).