I once implemented a communications protocol that worked with variable-length independent messages over TCP. It felt a little silly pushing distinct datagrams into a stream, that would be chopped up into a packets, sent to another PC, where the OS would then reassemble those packets back into a stream, only to be chopped up again in messages.

Implementing the system for chopping up the stream really felt like it should have been done by a lower level as well, not in an application