code: func DeleteOldStapleFiles() {
  	files, err := ioutil.ReadDir(ocspFolder)
  	if err != nil {
  		// maybe just hasn't been created yet; no big deal
  		return
  	}
  	for _, file := range files {
  		if file.IsDir() {
  			// weird, what's a folder doing inside the OCSP cache?
  			continue
  		}
  		stapleFile := filepath.Join(ocspFolder, file.Name())
  		ocspBytes, err := ioutil.ReadFile(stapleFile)
  		if err != nil {
  			continue
  		}
  		resp, err := ocsp.ParseResponse(ocspBytes, nil)
  		if err != nil {
  			// contents are invalid; delete it
  			err = os.Remove(stapleFile)
  			if err != nil {
  				log.Printf("[ERROR] Purging corrupt staple file %s: %v", stapleFile, err)
  			}
  		}
  		if time.Now().After(resp.NextUpdate) {
  			// response has expired; delete it
  			err = os.Remove(stapleFile)
  			if err != nil {
  				log.Printf("[ERROR] Purging expired staple file %s: %v", stapleFile, err)
  			}
  		}
  	}
  }
docs: // DeleteOldStapleFiles deletes cached OCSP staples that have expired.
  // TODO: Should we do this for certificates too?