code: func (s *CheckerStrategy) GetIP(req *http.Request) string {
  	if s.Checker == nil {
  		return ""
  	}
  
  	xff := req.Header.Get(xForwardedFor)
  	xffs := strings.Split(xff, ",")
  
  	for i := len(xffs) - 1; i >= 0; i-- {
  		xffTrimmed := strings.TrimSpace(xffs[i])
  		if contain, _ := s.Checker.Contains(xffTrimmed); !contain {
  			return xffTrimmed
  		}
  	}
  	return ""
  }
docs: // GetIP return the selected IP