code: func (journal *txJournal) insert(tx *types.Transaction) error {
  	if journal.writer == nil {
  		return errNoActiveJournal
  	}
  	if err := rlp.Encode(journal.writer, tx); err != nil {
  		return err
  	}
  	return nil
  }
docs: // insert adds the specified transaction to the local disk journal.