add FilesWithNames() to activation

[MayCXC]

I'd like to upstream the function here https://github.com/MayCXC/caddy-systemd-socket-activation/blob/master/networks.go#L25

which is like the *WithNames funcs here

go-systemd/activation/listeners.go

Line 42 in 7d375ec

func ListenersWithNames() (map[string][]net.Listener, error) {

, but with the benefit that it works for any network (tcp/udp/unix/unixgram/etc.) that a socket might be bound to, and lets the caller choose how to make a FileListener or FilePacketConn from them.

[prestist]

Thank you for contributing! Would you mind explaining your usecase ?

[MayCXC]

sure, my program uses socket units with both Listen and ListenDatagram settings, some of which may be used to create TLS listeners, and some of which may not. The existing *WithNames functions assume that all the sockets use the same protocol, and that either all or none will be used to create TLS listeners. FilesWithNames() provides the same LISTEN_FDS/LISTEN_FDNAMES mapping to files that the appropriate listeners can be created with, but without making these assumptions.