Example of middleware in GO

middleware.go

package main

import (
	"fmt"
	"os"
	"net/http"
	"log"
	"context"
	"time"
)

type Server struct {
	*http.ServeMux
}

func NewServer() *Server {
	return &Server{http.NewServeMux()}
}

func (s *Server) ServeHTTP(rw http.ResponseWriter, req *http.Request) {
	timeStart := time.Now()
	ctx := req.Context()
	ctx = context.WithValue(ctx, "name", "Rodrigo")

	req = req.WithContext(ctx)
	s.ServeMux.ServeHTTP(rw, req)
	timeEnd := time.Now().Sub(timeStart)
	log.Printf("Server execution time was %s.\n", timeEnd.String())
}

func main() {
	myServer := NewServer()
	myServer.HandleFunc("/welcome", welcome)
	myServer.HandleFunc("/hello", MiddlewareForRouter(hello))

	addr := ":8080"
	fmt.Printf("Server listing %s\n", addr)
	err := http.ListenAndServe(addr, myServer)
	if err != nil {
		log.Fatalf("Server Errror: %v", err)
		os.Exit(1)
	}

	os.Exit(0)
}

// MiddlewareForRouter is an example of middleware for routers.
func MiddlewareForRouter(handlerFunc http.HandlerFunc) http.HandlerFunc {
	return func(rw http.ResponseWriter, req *http.Request) {
		timeStart := time.Now()
		handlerFunc(rw, req)
		timeEnd := time.Now().Sub(timeStart)
		log.Printf("Middleware execution time was %s.\n", timeEnd.String())
	}
}

func welcome(w http.ResponseWriter, r *http.Request) {
	fmt.Fprintln(w, "Welcome Rodrigo")
}

func hello(w http.ResponseWriter, r *http.Request) {
	userName, has := r.Context().Value("name").(string)
	if has {
		fmt.Fprintf(w, "Welcome %v.", userName)
		return
	}

	w.WriteHeader(401)
	fmt.Fprintln(w, "User not logged")
}