code: func (d *DiskStorer) All() ([]string, error) {
  	files, err := ioutil.ReadDir(d.folderPath)
  	if err != nil {
  		return []string{}, errors.Wrapf(err, "unable to read directory: %s", d.folderPath)
  	}
  
  	sessions := make([]string, len(files))
  
  	for i := 0; i < len(files); i++ {
  		sessions[i] = files[i].Name()
  	}
  
  	return sessions, nil
  }
docs: // All keys in the disk store