docs: def filter_headers(data):
      """只设置host content-type 还有x开头的头部.
  
      :param data(dict): 所有的头部信息.
      :return(dict): 计算进签名的头部.
      """
      headers = {}
      for i in data:
          if i == 'Content-Type' or i == 'Host' or i[0] == 'x' or i[0] == 'X':
              headers[i] = data[i]
      return headers