code: func GetClientIP(req *http.Request) net.IP {
  	ips := SourceIPs(req)
  	if len(ips) == 0 {
  		return nil
  	}
  	return ips[0]
  }
docs: // Extracts and returns the clients IP from the given request.
  // Looks at X-Forwarded-For header, X-Real-Ip header and request.RemoteAddr in that order.
  // Returns nil if none of them are set or is set to an invalid value.