AF_LOCAL (Unix domain) sockets suck for datagram messaging because both end-points need a filesystem name -- you can't have the client end-point be anonymous! The simplest way to have an anonymous client is to send a datagram socketpair to the server in a datagram, this way the server can respond over the socketpair -- but this is complex and significantly slower than if Unix domain datagram sockets just supported anonymous clients.
Meanwhile, if you want to write an IPC library that's portable to WIN32 and POSIX, and just about any OS that supports TCP/IP, then TCP or UDP works very well. In fact, nothing else does. But of course, you have to publish the server port number (and at least a cookie for authentication) for this somewhere (e.g., in /tmp).
