Basic golang mux router with middleware

init.go

package main

import (
	"context"
	"fmt"
	"log"
	"net/http"

	"github.com/gorilla/mux"
)

type messageKey struct{}

func myMiddleware(next http.Handler) http.Handler {
	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
		ctx := r.Context()

		req := r.WithContext(context.WithValue(ctx, messageKey{}, "hello world"))
		next.ServeHTTP(w, req)
	})
}

func handler(w http.ResponseWriter, r *http.Request) {
	ctx := r.Context()
	if message, ok := ctx.Value(messageKey{}).(string); ok {
		fmt.Fprintf(w, "The message is '%s'", message)
	} else {
		fmt.Fprintf(w, "No message received :(")
	}
}

func main() {
	r := mux.NewRouter()
	r.Use(myMiddleware)
	r.HandleFunc("/hi", handler).Methods("GET")
	http.Handle("/", r)
	log.Fatal(http.ListenAndServe(":5000", nil))
}