What's so wrong with POSIX sockets? It's maybe not an elegant API, but not because "it's designed for C". It's problems are for example 1) it's doing too much abstraction (sockets). 2) you have to deal with some arcane data structures and ancient formats (endian conversions).

But, it does its job well enough: allowing the user to send and receive packets from the network.

If you're writing a networked application that works, chances are you either don't give a sh*t what API to use as long as it lets you send and receive packets (and thus you go with the relatively portable POSIX sockets (at least for Linux / WinSock2 on Windows)), or you use a lower-level API (probably proprietary) to reduce syscall overhead / get more control.

If you're parsing text, chances are all you need is fread() to read in the next chunk from a file, and from this you'll build a "next_byte()" function and then a "next_token()" function on top.

(I've done a lot of network code as well as parsing code, and the I/O API is among the least of my concerns).

All these fancy bottom-up kitchen sink libraries implementing "proper abstractions" or whatever do not provide any value past being able to be combined to form barely working and un-fixable applications where you will pull your hair out when you actually need some control over what's happening.

For something better, you'll need exactly this from external libraries: a clean programmatic (function call) interface that gives you control at a reasonable level of abstraction.