I'm confused. Are you saying additional piping is fast (even beating URL rewriting), or is it not?

I expect piping a file through the application and the webserver to be way slower than calling sendfile() or similar from the webserver to let the OS kernel deliver the file directly from the buffer cache to the network interface. URL rewriting happens before any resource is delivered and adds extra time, no matter how the requested resource is delivered. To see which of rewrite + sendfile() and application-piping is faster, you need to benchmark. I guess that for simple rewriting operations and a "warm" buffer cache, the first way still is faster. Naturally, if you get rid of the rewriting, it will be even faster.

But if speed is not the only problem (e.g. because the resources need to be protected by some application logic), you sometimes simply can't leave content delivery to the webserver alone. You either need to deliver the content through the application, or ideally have a way to instruct the webserver from your application to deliver a local file, bypassing all existing protection rules inside the webserver. lighttpd and mod_xsendfile for Apache support a propritary X-Sendfile header to do exactly this. nginx has a similar feature.

Alexander