如何使用反向代理获取当前打开的TCP连接数

Question

I have the following simple reverse proxy:

func main() {
    go func() {
        for range time.NewTicker(30 * time.Second).C {
            log.Println("NUMBER OF OPEN CONNECTIONS")
        }
    }()

    http.HandleFunc("/", handleRequestAndRedirect)
    if err := http.ListenAndServe(getListenAddress(), nil); err != nil {
        panic(err)
    }
}

func handleRequestAndRedirect(res http.ResponseWriter, req *http.Request) {
    serveReverseProxy("https://example.com", res, req)
}

func serveReverseProxy(target string, res http.ResponseWriter, req *http.Request) {
    url, _ := url.Parse(target)
    req.URL.Host = url.Host
    req.URL.Scheme = url.Scheme
    req.Host = url.Host

    proxy := httputil.NewSingleHostReverseProxy(url)
    proxy.ServeHTTP(res, req)
}

All I am trying to figure out how to do is print the current number of open TCP connections every 30 seconds. Is there some property I can access in http or httputil to do this? Is there a way I can track this myself with minimal modifications to the code?

Thanks.