docs: def parse_message(xml):
      """
      解析微信服务器推送的 XML 消息
  
      :param xml: XML 消息
      :return: 解析成功返回对应的消息或事件，否则返回 ``UnknownMessage``
      """
      if not xml:
          return
      message = xmltodict.parse(to_text(xml))['xml']
      message_type = message['MsgType'].lower()
      event_type = None
      if message_type == 'event' or message_type.startswith('device_'):
          if 'Event' in message:
              event_type = message['Event'].lower()
          # special event type for device_event
          if event_type is None and message_type.startswith('device_'):
              event_type = message_type
          elif message_type.startswith('device_'):
              event_type = 'device_{event}'.format(event=event_type)
  
          if event_type == 'subscribe' and message.get('EventKey'):
              event_key = message['EventKey']
              if event_key.startswith(('scanbarcode|', 'scanimage|')):
                  event_type = 'subscribe_scan_product'
                  message['Event'] = event_type
              elif event_key.startswith('qrscene_'):
                  # Scan to subscribe with scene id event
                  event_type = 'subscribe_scan'
                  message['Event'] = event_type
                  message['EventKey'] = event_key[len('qrscene_'):]
          message_class = EVENT_TYPES.get(event_type, UnknownMessage)
      else:
          message_class = MESSAGE_TYPES.get(message_type, UnknownMessage)
      return message_class(message)