text: from flask_restful.utils.crypto import decrypt, encrypt
  DEFAULT_PAGE_SIZE = 50
  
  
  def retrieve_next_page(key, seed, args, callback, initial_bookmark=None):
      """
      A helper for the bookmark pager.
  
      :param key: the private key of you API
      :param seed: the crypo seed for this session
      :param args: the verbatim filtering+paging arguments
      :param callback: a function that takes (a dictionary of filters, the current bookmark, the page size)
                   and return a tuple (next_results, dictionary_ready_for_next_iteration, approx_number_of_element_left)
      :param initial_bookmark: pass here an optional initial bookmark for the first request
      :return: the tuple result_list and new encrypted bookmark
      """
      filter = dict(args)
      if 'pager_info' in filter:
          initial_bookmark = decrypt(filter.pop('pager_info'), key, seed)
  
      page_size = filter.pop('page_size', DEFAULT_PAGE_SIZE)
  
      result_list, new_bookmark, approx_result_size = callback(filter, initial_bookmark, page_size)
  
      # restore for the next iteration
      filter['pager_info'] = encrypt(new_bookmark, key, seed)
      filter['page_size'] = page_size
  
      return result_list, filter, approx_result_size
  