Regarding URL rewriting: DON'T, if you want maximum performance. Avoid any work that is not absolutely needed, both in the webserver setup and in your program. If you need to protect images from unauthorised access, pipe those through your application or use the webserver's access control methods.

As an alternative to URL rewriting (which can be done inside the webserver), for performance reasons, you suggest piping the images through the application? Earlier you said:

If you want top performance, you should let the webserver and the operating system cooperate to handle delivery of images, so that sendfile() and similar functions can be used, ideally delivering the file directly from the buffer cache to the network card without any additional copying (zero copy).

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

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