code: func FileContentHash(filename string) (string, error) {
  	f, err := os.Open(filename)
  	if err != nil {
  		return "", err
  	}
  	defer f.Close()
  	return ContentHash(f)
  }
docs: // FileContentHash returns the Dropbox content_hash for a local file.
  // See https://www.dropbox.com/developers/reference/content-hash