code: func (db *DB) Has(key []byte, ro *opt.ReadOptions) (ret bool, err error) {
  	err = db.ok()
  	if err != nil {
  		return
  	}
  
  	se := db.acquireSnapshot()
  	defer db.releaseSnapshot(se)
  	return db.has(nil, nil, key, se.seq, ro)
  }
docs: // Has returns true if the DB does contains the given key.
  //
  // It is safe to modify the contents of the argument after Has returns.