Florian Klink 861c01caf5 http: support listening on passed FDs
Instead of the listening addresses specified above, rclone will listen to all
FDs passed by the service manager, if any (and ignore any arguments passed by
`--{{ .Prefix }}addr`.

This allows rclone to be a socket-activated service. It can be configured as described in
https://www.freedesktop.org/software/systemd/man/latest/systemd.socket.html

It's possible to test this interactively through `systemd-socket-activate`,
firing of a request in a second terminal:

```
❯ systemd-socket-activate -l 8088 -l 8089 --fdname=foo:bar -- ./rclone serve webdav :local:test/
Listening on [::]:8088 as 3.
Listening on [::]:8089 as 4.
Communication attempt on fd 3.
Execing ./rclone (./rclone serve webdav :local:test/)
2024/04/24 18:14:42 NOTICE: Local file system at /home/flokli/dev/flokli/rclone/test: WebDav Server started on [sd-listen:bar-0/ sd-listen:foo-0/]
```
2024-09-06 17:21:56 +01:00
..
2022-12-15 12:38:09 +00:00