docs: def log(host=None, port=None, limit=0):
      """view log of web server"""
      app.config['HOST'] = first_value(host, app.config.get('HOST',None), '0.0.0.0')
      app.config['PORT'] = int(first_value(port, app.config.get('PORT',None), 5001))
      if app.config['HOST'] == "0.0.0.0": 
          host="127.0.0.1"
      else:
          host = app.config['HOST']
      port = app.config['PORT']    
      try:
          res = requests.get('http://%s:%s/api/log?limit=%s' % (host, port, limit))
          if res.status_code == 200:
              for record in json.loads(res.text):
                  if record['level'] >= 30:
                      print(record['msg'], file=sys.stderr)
                  else:    
                      print(record['msg'], file=sys.stdinfo)
          else:
              print('web server is not flaskserver', file=sys.stderr)
      except:
          print('web server is not flaskserver or not start', file=sys.stderr)