Have you seen Richard W. Stevens book TCP/IP Illustrated? Specifically volume 2 'the Implementation', which is, I think what you're looking for (albeit slightly dated).

Yes I own the series but their focus is a little more on completeness. I know I'm getting picky :) but TCP is pretty complex so I keep looking out for the most minimal code and walk through to understand all the state management and other flow.

Take a look at Adam Dunkels' lwIP and uIP - http://dunkels.com/adam/software.html.

Also Jeremy Bentham's TCP/IP Lean: Web Servers for Embedded Systems is pretty good.

Woah, I love Adam's work. Thanks for sharing.

Not a tutorial but did you look at PicoTCP ?

https://github.com/tass-belgium/picotcp

That version is abandoned and has quite a few severe bugs. There is a GPL fork which is maintained https://github.com/virtualsquare/picotcp

In addition to the Stevens books already mentioned, there's also volume 2 of Comer's Xinu OS book:

Operating System Design, Vol. 2: Internetworking with Xinu, ISBN-13: 978-0136374145 (https://www.amazon.com/Operating-System-Design-Vol-Internetw...).

Unfortunately, this book was written in 1987, so it's a bit dated (e.g. no IPv6). I think it's still useful to learn the basics of a TCP/IP implementation.

Interesting, thanks for the reference.

Jon Gjengset has a series of videos implementing TCP in Rust.

https://youtu.be/bzja9fQWzdA