code: func NewSourceFromDatabase(
  	dbMap dbSelector,
  	caKeyHash []byte,
  	reqSerialPrefixes []string,
  	timeout time.Duration,
  	log blog.Logger,
  ) (src *DBSource, err error) {
  	src = &DBSource{
  		dbMap:             dbMap,
  		caKeyHash:         caKeyHash,
  		reqSerialPrefixes: reqSerialPrefixes,
  		timeout:           timeout,
  		log:               log,
  	}
  	return
  }
docs: // NewSourceFromDatabase produces a DBSource representing the binding of a
  // given DB schema to a CA key.