code: func (db *nodeDB) expirer() {
  	tick := time.NewTicker(nodeDBCleanupCycle)
  	defer tick.Stop()
  	for {
  		select {
  		case <-tick.C:
  			if err := db.expireNodes(); err != nil {
  				log.Error(fmt.Sprintf("Failed to expire nodedb items: %v", err))
  			}
  		case <-db.quit:
  			return
  		}
  	}
  }
docs: // expirer should be started in a go routine, and is responsible for looping ad
  // infinitum and dropping stale data from the database.