Trying to understand my network performance in detail (in particular, the state of my TCP connections) is so much fun.
"The best documentation you can get is to look at your kernel's source […]" (http://linuxgazette.net/136/pfeiffer.html) - Yay, source code as documentation, I love this! </sarcasm>

Just in case you're interested, this approach here using the "socketstat" utility seems way easier than compiling/writing your own program: https://blog.janestreet.com/inspecting-internal-tcp-state-on-linux/