code: func (m *Manager) Snapshot(path string) error {
  	m.lock.Lock()
  	defer m.lock.Unlock()
  	return m.snapshot(path, false)
  }
docs: // Snapshot will persist a snapshot of the proxy manager state that
  // can be restored with Restore.
  //
  // If DataDir is non-empty, then the Manager will automatically snapshot
  // whenever the set of managed proxies changes. This method generally doesn't
  // need to be called manually.