Don't reset rclone rate limit when not needed

[Michal-Leszczynski]

Rclone server has globalConfigGuard that should update rate limit / transfers used by the agent only when the update is actually changing the value. Otherwise, we perform unnecessary re-initialization, which might be costly.

Here are logs from an SCT test running 2 backups and restore:

2024-10-28T13:30:00.620+00:00  {"L":"INFO","T":"2024-10-28T13:30:00.163Z","N":"rclone","M":"Location check done"}
2024-10-28T13:30:02.870+00:00  {"L":"INFO","T":"2024-10-28T13:30:02.606Z","N":"rclone","M":"Bandwidth limit set to {100M 100M}"}
2024-10-28T13:30:04.370+00:00  {"L":"INFO","T":"2024-10-28T13:30:04.021Z","N":"rclone","M":"Bandwidth limit set to {100M 100M}"}
2024-10-28T13:32:19.370+00:00  {"L":"INFO","T":"2024-10-28T13:32:19.015Z","N":"rclone","M":"Bandwidth limit set to {100M 100M}"}
2024-10-28T13:32:20.620+00:00  {"L":"INFO","T":"2024-10-28T13:32:20.307Z","N":"rclone","M":"Bandwidth limit set to {100M 100M}"}
2024-10-28T13:32:21.620+00:00  {"L":"INFO","T":"2024-10-28T13:32:21.340Z","N":"rclone","M":"Bandwidth limit set to {100M 100M}"}
2024-10-28T13:32:22.620+00:00  {"L":"INFO","T":"2024-10-28T13:32:22.424Z","N":"rclone","M":"Bandwidth limit set to {100M 100M}"}
2024-10-28T13:32:23.756+00:00  {"L":"INFO","T":"2024-10-28T13:32:23.585Z","N":"rclone","M":"Bandwidth limit set to {100M 100M}"}
2024-10-28T13:33:24.370+00:00  {"L":"INFO","T":"2024-10-28T13:33:23.905Z","N":"rclone","M":"Location check done"}
2024-10-28T13:33:25.620+00:00  {"L":"INFO","T":"2024-10-28T13:33:25.166Z","N":"rclone","M":"Bandwidth limit set to {100M 100M}"}
2024-10-28T13:33:26.790+00:00  {"L":"INFO","T":"2024-10-28T13:33:26.642Z","N":"rclone","M":"Bandwidth limit set to {100M 100M}"}
2024-10-28T13:33:26.790+00:00  {"L":"INFO","T":"2024-10-28T13:33:26.644Z","N":"rclone","M":"There was nothing to transfer"}
2024-10-28T13:33:41.870+00:00  {"L":"INFO","T":"2024-10-28T13:33:41.589Z","N":"rclone","M":"Location check done"}
2024-10-28T13:33:57.621+00:00  {"L":"INFO","T":"2024-10-28T13:33:57.183Z","N":"rclone","M":"Bandwidth limit reset to unlimited"}
2024-10-28T13:34:32.370+00:00  {"L":"INFO","T":"2024-10-28T13:34:32.105Z","N":"rclone","M":"Bandwidth limit reset to unlimited"}
2024-10-28T13:34:59.621+00:00  {"L":"INFO","T":"2024-10-28T13:34:59.513Z","N":"rclone","M":"Bandwidth limit reset to unlimited"}
2024-10-28T13:35:23.370+00:00  {"L":"INFO","T":"2024-10-28T13:35:23.040Z","M":"http: TLS handshake error from 10.12.1.124:45446: EOF"}
2024-10-28T13:35:27.871+00:00  {"L":"INFO","T":"2024-10-28T13:35:27.633Z","N":"rclone","M":"Bandwidth limit reset to unlimited"}
2024-10-28T13:35:57.120+00:00  {"L":"INFO","T":"2024-10-28T13:35:56.914Z","N":"rclone","M":"Bandwidth limit reset to unlimited"}
2024-10-28T13:36:28.621+00:00  {"L":"INFO","T":"2024-10-28T13:36:28.179Z","N":"rclone","M":"Bandwidth limit reset to unlimited"}
2024-10-28T13:36:58.120+00:00  {"L":"INFO","T":"2024-10-28T13:36:57.811Z","N":"rclone","M":"Bandwidth limit reset to unlimited"}
2024-10-28T13:37:33.621+00:00  {"L":"INFO","T":"2024-10-28T13:37:33.341Z","N":"rclone","M":"Bandwidth limit reset to unlimited"}
2024-10-28T13:37:58.620+00:00  {"L":"INFO","T":"2024-10-28T13:37:58.332Z","N":"rclone","M":"Bandwidth limit reset to unlimited"}
2024-10-28T13:38:12.871+00:00  {"L":"INFO","T":"2024-10-28T13:38:12.726Z","N":"rclone","M":"Bandwidth limit reset to unlimited"}

We can see that rate limit has been updated multiple times, even though there was no need for it.

In the implementation we can see:

// SetBandwidthLimit sets global bandwidth limit in token bucket.
func SetBandwidthLimit(limit string) error {
	globalConfigGuard.mu.Lock()
	defer globalConfigGuard.mu.Unlock()
	globalConfigGuard.init()

	if limit == globalConfigGuard.bandwidthLimit {
		return nil
	}

	in := rc.Params{
		"rate": limit,
	}
	_, err := rcCalls.Get("core/bwlimit").Fn(context.Background(), in)
	if err != nil {
		return errors.Wrapf(err, "set bandwidth to %s", limit)
	}
	return nil
}

We simply forgot to update the value cached in globalConfigGuard after setting it with core/bwlimit call.