m-socket

Description

This Common Lisp package implements some features of TCP-based socket system. It is based on CFFI (as opposed to using host Lisp system's features like many other socket libraries do). Currently you can't make connections with it but you can listen for new connections.

Features an I/O multiplexer feature that lets you efficiently check the status of many sockets at once. The Linux backend is based on epoll() system call.

The user of the library is able to assume nothing ever blocks. None of the calls (with a small exception, see below for known problems) block. If something does block, it is a bug.

There is no global state internally inside the library, so it should be possible to use any of the functions from any threads, as long as they don't touch each other's sockets or I/O multiplexers at the same time.

Licensed under the ISC license. See LICENSE for copyright information.

Example usage

There is some example code in example.lisp file. Load that file to run it.

Installation

This package meant to be used through ASDF. Put the code somewhere where ASDF can find it. You also need to install m-util as this package depends on it.

(asdf:operate 'asdf:load-op "m-socket")

Known problems

Only works on Linux. Porting to FreeBSD shouldn't be hard; an I/O multiplexer based on kqueue() would have to be written. Porting to Windows is probably more involved for various reasons such as that platform using a different way to report socket errors.
There is an efficiency problem related to the use of system calls directly. The code has to convert arrays outside Lisp heap (that is, CFFI arrays to native Lisp arrays). This happens at every send and receive call. In my initial tests, it is not noticeable unless there is very large amounts of traffic. It might be useful to do some profiling here.
Conversion of hostnames to IP addresses blocks, unlike any other call in the library. This can happen in MAKE-LISTENER-SOCKET. Later, if connecting capabilities are added to the library, this problem has to be addressed if there's a desire for a non-blocking but convenient CONNECT call.
Tested on SBCL, Clozure CL and CLISP. More testing would be useful.

Author