如何在Go中获取空闲和“活动”连接的数量？

Assuming I have a regular HTTP Server in Go. How can I get the currently idle and active TCP connections?

httpServer := &http.Server{
    Handler: newHandler123(),
}

l, err := net.Listen("tcp", ":8080")
if err != nil {
    log.Fatal(err)
}

err = httpServer.Serve(l)
if err != nil {
    log.Fatal(err)
}