test.go

package main

import (
    "net/http"
)

func main() {
    srv := &http.Server{Addr: ":443", Handler: http.HandlerFunc(handle)}
    srv.ListenAndServeTLS("fullchain.pem", "privkey.pem")
}

func handle(w http.ResponseWriter, r *http.Request) {
    w.WriteHeader(200)
    w.(http.Flusher).Flush()
}