Have something like WAYLAND_SOCKET

In libwayland WAYLAND_DISPLAY names a listening socket like LIBEI_SOCKET, WAYLAND_SOCKET refers to an fd number of an already opened socket. It would be nice for libei to have a similar mechanism.

Motivation and Background:

A compositor might want to allow a specific client to always connect without having to expose a listening socket. We want to do this for Xwayland as xdg-desktop-portaldoes not provide any info that the process that wants to connect is Xwayland. Doing it this it's possible to know that Xwayland wants to connect to EIS and the eis_client name provides info about the X client.

I am looking at a workaround/HACK

const char *socketName = "/an/absolute/path";
eis_setup_backend_socket(eis, socketName);
int fd = open(socketName, O_PATH | O_CLOEXEC)
unlink(socketName);
[...]
setenv("LIBEI_SOCKET", "/proc/self/fd/fd");
// remove cloexec after fork

this is ugly and opens a listening socket that is publically accessible for a short amount of time