Here will be a collection of the simplest possible TCP chat servers, to demonstrate how to write multiuser, multiplexing server software using various techniques.

A yoctochat server will:

• take a single commandline argument, the port to listen on
• open a listening port
• handle multiple connections and disconnections on that port
• receive text on a connection, and forward it on to all other connections
• produce simple output about what its doing
• demonstrate a single IO multiplexing technique as simply as possible
• be well commented!

20+ years ago, during my University days, I started writing little chat servers like this to teach myself C, UNIX, systems programming, internet programming, and so on. I went on to write bigger and better ones. It has been useful knowledge!

Lately, I found myself wanting to experiment with io_uring, and I realised I'd forgotten how the "classic" select() loop is constructed. So I started there, and here we are!