I bought a copy of "The Book of PF" from @pitrh
It's the best and most comprehensive resource about the marvelous PF firewall that I've ever seen, and I've been using PF since the early days.
Amazing work!
It's available here on No Starch Press: https://nostarch.com/book-of-pf-4th-edition
I also recently wrote a practical guide on PF (https://blog.hofstede.it/pf-firewall-on-freebsd-a-practical-guide/) for anyone who wants to get started :-)
