How do I rewrite attachment urls when permalink structure contains %category%?

Question

I'm trying to change the permalinks to my attachments in the same way as this question, and the given solution works great except for one problem: if the permalinks settings on my site contain %category%, the solution doesn't work at all and I get a "This page isn't redirecting properly" error. The only way I can get this solution to work properly is by using the provided "Day and Name", "Month and Name", and "Numeric" permalink settings.

What do I add to the solution so that still use %category% in my custom permalink settings?

Answer 1

It seems like what I want is something that WordPress's internal permalink code isn't prepared to deal with. After reading this writeup by Otto, I've come to understand that having my permalinks start with %category% could create a performance issue down the road and I would have to create a function that further alters the WordPress permalink rules in order to get the attachment permalinks working with %category%.

As a result, I've decided to start all my posts with the year. This allows me to use the solution found here for attachment permalinks, and I'll avoid performance headaches in the future.