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.

[kolyshkin]

From what I see, this is just a wrapper on top of Files which converts the returned *os.File slice into a map, where the key is file name and the value is a slice of *os.File corresponding to this name.

Such functionality, if needed, can easily be recreated in software that uses this package and activation.Files, in just a few lines of code. Unless such usage is a very common case, I can hardly see why we should put this method into this repo.

[MayCXC]

From what I see, this is just a wrapper on top of Files which converts the returned *os.File slice into a map, where the key is file name and the value is a slice of *os.File corresponding to this name.

Such functionality, if needed, can easily be recreated in software that uses this package and activation.Files, in just a few lines of code. Unless such usage is a very common case, I can hardly see why we should put this method into this repo.

right, these are those few lines of code. there are already funcs in activation that create TCP listeners with TLS configurations for each stream fd and map names to them, which is a much more special case than what FilesWithNames handles. for example, http3 web servers that use socket activation will receive file descriptors for two TCP sockets and one UDP socket, the latter of which will have its name ignored as there is no PacketConnsWithNames func in activation. so in general a map of fd names to files is a more useful construct for working with socket activation.

[kolyshkin]

@MayCXC can you please squash your commits, and add a activation: prefix to the commit subject?

[MayCXC]

@kolyshkin no problem. i also moved the func out of the goos targets.

[kolyshkin]

lgtm

[Luap99]

I think that could be made much simpler with just doing

filesWithNames[f.Name()] = append(filesWithNames[f.Name()], f)

The map lookup returns the zero value nil which is totally fine to append to and will create a new slice and otherwise returns the existing one and appends there so this one line should be enough

[MayCXC]

seems so, that was copied from the other funcs:

go-systemd/activation/listeners.go

Line 48 in 4b765dd

current, ok := listeners[f.Name()]

[kolyshkin]

Opened #498

[kolyshkin]

FYI, this PR is being carried in #497