I don't quite understand. TCP is hard because the state machine itself is complex. Parsing actual messages is trivial in comparison. One can just compare the le

I don't quite understand. TCP is hard because the state machine itself is complex. Parsing actual messages is trivial in comparison. One can just compare the length of the segment format description (a couple of pages in the original RFC) with the combined length of numerous RFCs detailing TCP behavior in various corner cases.