package main

import (
  "net/http"
  "strings"
  "fmt"
  "github.com/gorilla/mux"
  "golang.org/x/net/http2"
)

func sayHello(w http.ResponseWriter, r *http.Request) {
  message := r.URL.Path
  message = strings.TrimPrefix(message, "/")
  message = "Hello " + message

  w.Header().Set("myFirst", "golangQuestion")
  w.Write([]byte(message))
  for k, v := range w.Header() {
    fmt.Println("[RESPONSE][Header]", k,":", v)
    }
}

func main() {
    router := mux.NewRouter()
    router.PathPrefix("/").HandlerFunc(sayHello) // catch everything else rule
    var srv = &http.Server{
        Addr: "127.0.0.1:8081",
    }
    http2.ConfigureServer(srv, nil)
    srv.Handler = router
    sslCert := "./ssl.cert"
    sslKey := "./ssl.key"
    if err := srv.ListenAndServeTLS(sslCert, sslKey); err != nil {
        panic(err)
    }
}

HTTP/1.1 200 OK
Myfirst: golangQuestion
Date: Tue, 18 Jun 2019 09:18:29 GMT
Content-Length: 6
Content-Type: text/plain; charset=utf-8

[RESPONSE][Header] Myfirst : [golangQuestion]

for k, v := range w.Header() {
    fmt.Println("[RESPONSE][Header]", k,":", v)
    }

[RESPONSE][Header] Myfirst : [golangQuestion]
[RESPONSE][Header] Date: [2019.02.12 ]
[RESPONSE][Header] Content-Length: [6]