Use XDG_CACHE_HOME by default.

[ghost]

As you use '~/.config/vis' directory for vis, what about following XDG for location of FIFO? This is just a proposition.

We can set ABDUCO_SOCKET_DIR or edit config.h anyway.

What other programs do: http://wiki.archlinux.org/index.php/XDG_Base_Directory_support

[martanne]

I don't think $XDG_CACHE_HOME is appropriate because we are not dealing with "non-essential data files".

Regarding $XDG_RUNTIME_DIR, the XDG specification defines its lifetime in terms of logins/logouts. The abduco socket obviously has to survive that, otherwise it isn't possible to resume a session. Hence, it also does not seem useful for our case.

Unless I'm misunderstanding how they define login/logout?

[ilyagr]

Perhaps XDG_STATE_HOME is a better place for it according to XDG. At least, https://specifications.freedesktop.org/basedir-spec/latest/#variables and https://wiki.archlinux.org/title/XDG_Base_Directory make it seem like a reasonable place. Abduco session seems close enough to data that needs to "survive application restart" (especially if you consider a detach/reattach cycle as a "restart" of a "client").

Though, looking at this PR, it would be a bit strange to use an XGD_STATE_HOME (or XDG_CACHE_HOME, as currently implemented) environment variable, but not to use the default value for it suggested in https://specifications.freedesktop.org/basedir-spec/latest/#variable .