docs: def decrypt(self, text, app_id):
          """
          对密文进行解密
          :param text: 需要解密的密文
          :param app_id: 微信公众平台的 AppID
          :return: 解密后的字符串
          """
          text = to_binary(text)
          decryptor = self.cipher.decryptor()
          plain_text = decryptor.update(base64.b64decode(text)
                                        ) + decryptor.finalize()
  
          padding = byte2int(plain_text, -1)
          content = plain_text[16:-padding]
  
          xml_len = socket.ntohl(struct.unpack("I", content[:4])[0])
          xml_content = content[4:xml_len + 4]
          from_appid = content[xml_len + 4:]
  
          if to_text(from_appid) != app_id:
              raise AppIdValidationError(text, app_id)
  
          return xml_content