Basis Golang HTTP REST server - Best practices interpreted

main.go

/*
Based on the video's and blogposts of Mat Ryer (@matryer)..

- https://pace.dev/blog/2018/05/09/how-I-write-http-services-after-eight-years.html
- https://www.youtube.com/watch?v=FkPqqakDeRY
- https://www.youtube.com/watch?v=rWBSMsLG8po

.. I derived the following starting point for a GO HTTP REST server. It can be used to add all explained (see above) concepts.

You could spread the code below in separate files as follows:
├── cmd
│   └── main.go
├── handle_index.go
├── handle_index_test.go
├── routes.go
└── server.go
*/

package main

import (
	"encoding/json"
	"fmt"
	"log"
	"net/http"

	"github.com/gorilla/mux"
)

func main() {
	NewServer()
}

// -------------------   server.go
type server struct {
	router *mux.Router
}

// NewServer creates a server with router and does all things from here
func NewServer() {
	s := &server{mux.NewRouter()}
	s.routes()
	log.Fatalln(http.ListenAndServe(":8080", s.router))
}

// -------------------   routes.go
func (s *server) routes() {
	s.router.HandleFunc("/", s.handleIndex())
	s.router.HandleFunc("/admin-ok", s.handleAdmin())
	s.router.HandleFunc("/admin-not-ok", s.adminOnly(s.handleAdmin()))
}

// -------------------   Handle functions below

func (s *server) handleIndex() http.HandlerFunc {
	// Let's do some JSON output here
	type response struct {
		Greeting string `json:"greeting"`
	}
	return func(w http.ResponseWriter, r *http.Request) {
		greet := response{"Hello world"}
		js, err := json.Marshal(greet)
		if err != nil {
			http.Error(w, err.Error(), http.StatusInternalServerError)
			return
		}

		w.Header().Set("Content-Type", "application/json")
		w.Write(js)

	}
}

func (s *server) handleAdmin() http.HandlerFunc {
	// Here you can prepare a 'private thing' to use in the
	return func(w http.ResponseWriter, r *http.Request) {
		fmt.Fprintf(w, "Hello Admin!")
	}
}

func (s *server) adminOnly(h http.HandlerFunc) http.HandlerFunc {
	return func(w http.ResponseWriter, r *http.Request) {
		if true { // instead of "true" e.g. "!currentUser(r).IsAdmin"
			http.NotFound(w, r)
			return
		}
		h(w, r)
	}
}