server.go

package main
import "net/http"
func main() {
    	changeHeaderThenServe := func(h http.Handler) http.HandlerFunc {
            	return func(w http.ResponseWriter, r *http.Request) {
       	             h.ServeHTTP(w, r)
            	}
    	}
    	http.Handle("/", changeHeaderThenServe(http.FileServer(http.Dir("."))))
    	http.ListenAndServe(":8000", nil)
}