Module ipc::uds

#include <std/ipc/uds.h> source

Unix Domain Sockets

Named, addressable IPC between unrelated processes (unlike pipe.h's anonymous pipes, which only work between a process and something that already has the fds — typically a fork()'d child): any process that knows the filesystem path can connect, the same way any process that knows a TCP port can connect to std/sched/io_nb.h's tcp_listen_nb. Deliberately the same non-blocking, std::Reactor-pairable shape as io_nb.h's tcp_*_nb functions — a task calls one of these, gets EAGAIN/EWOULDBLOCK immediately instead of blocking the whole program, and awaits readiness via TaskScheduler::await_fd(fd, SCHED_READ/ SCHED_WRITE) instead.

Windows has no AF_UNIX-domain-socket equivalent in the traditional BSD-sockets sense (Windows 10 1803+ does support AF_UNIX, but not universally across the target versions this project otherwise supports), so there's no uds_win32.sc — named pipes (a different API shape entirely: CreateNamedPipe/ConnectNamedPipe, not socket/bind/ listen/accept/connect) are Windows' native equivalent for this use case, and would need their own, differently-shaped module rather than slotting into this one's function signatures.

Backends:

uds_bsd.sc    — macOS, iOS, FreeBSD (struct sockaddr_un has a leading
                1-byte sun_len field, matching sockaddr_in's BSD
                quirk in std/sched/io_nb_bsd.sc)
uds_linux.sc  — Linux, Android (no sun_len; plain 2-byte sun_family)

Functions

uds_listen_nb	socket()+bind()+listen() on 'path', non-blocking. Returns the listening fd, or -1 on failure. Fails with EADDRINUSE if 'path' already exists as a socket file from a previous run that didn't clean up — call uds_unlink(path) first if that's a possibility.
uds_accept_nb	Non-blocking accept(): returns a connected client fd (itself set non-blocking), or -1 with errno EAGAIN/EWOULDBLOCK if none is pending yet — the caller should await_fd(listenfd, SCHED_READ) and retry.
uds_connect_nb	socket()+connect() to 'path', non-blocking: connect() on a non-blocking socket returns immediately with EINPROGRESS rather than waiting for the handshake — the caller should await_fd(fd, SCHED_WRITE) and treat the fd becoming writable as "connect finished". Returns the socket fd, or -1 on immediate failure.
uds_unlink	Removes a stale socket file at 'path' (unlink(2)) — a Unix domain socket's bind() fails EADDRINUSE if the filesystem path from a previous, uncleanly-terminated run still exists, unlike a TCP port which is simply released by the OS. Returns 0 on success (including "path didn't exist"), -1 on a real failure.