Systemd socket activation for rclone serve

I'd like to create some rclone serve processes, and use systemd socket activation to start them on demand.

Essentially, sockets are passed as FDs directly to the process.

systemd socket activation in Go · Graham King describes a golang-only solution to implement this.

It'd be nice if rclone would support this too. In the presence of the LISTEN_PID env var, it could automatically bind to FD 3 - or the --addr CLI arg could get additional syntax for this, similar to the (undocumented in the --help output) unix:// syntax.

This is implemented in http: support listening on passed FDs by flokli · Pull Request #7801 · rclone/rclone · GitHub, PTAL.