code: func backupFormat(w http.ResponseWriter, r *http.Request) (store.BackupFormat, error) {
  	fmt, err := fmtParam(r)
  	if err != nil {
  		return store.BackupBinary, err
  	}
  	if fmt == "sql" {
  		w.Header().Set("Content-Type", "application/sql")
  		return store.BackupSQL, nil
  	}
  	w.Header().Set("Content-Type", "application/octet-stream")
  	return store.BackupBinary, nil
  }
docs: // backuFormat returns the request backup format, setting the response header
  // accordingly.