code: func (s *DepthStrategy) GetIP(req *http.Request) string {
  	xff := req.Header.Get(xForwardedFor)
  	xffs := strings.Split(xff, ",")
  
  	if len(xffs) < s.Depth {
  		return ""
  	}
  	return strings.TrimSpace(xffs[len(xffs)-s.Depth])
  }
docs: // GetIP return the selected IP