code: func GetLog(c context.Context, host, taskID, logname string) (text string, closed bool, err error) {
  	switch {
  	case taskID == "":
  		err = errors.New("no swarming task id", grpcutil.InvalidArgumentTag)
  		return
  	case logname == "":
  		err = errors.New("no log name", grpcutil.InvalidArgumentTag)
  		return
  	}
  
  	sf, err := NewProdService(c, host)
  	if err != nil {
  		return
  	}
  
  	return swarmingBuildLogImpl(c, sf, taskID, logname)
  }
docs: // GetLog loads a step log.