d3.go

type Middleware func(http.HandlerFunc) http.HandlerFunc

func LoggingMiddleware(next http.HandlerFunc) http.HandlerFunc {
    return func(w http.ResponseWriter, r *http.Request) {
        log.Println("Before request")
        next.ServeHTTP(w, r)
        log.Println("After request")
    }
}

func AuthMiddleware(next http.HandlerFunc) http.HandlerFunc {
    return func(w http.ResponseWriter, r *http.Request) {
        user := r.Header.Get("X-User")
        if user == "" {
            http.Error(w, "Unauthorized", http.StatusUnauthorized)
            return
        }
        ctx := context.WithValue(r.Context(), "user", user)
        next.ServeHTTP(w, r.WithContext(ctx))
    }
}

func MyHandler(w http.ResponseWriter, r *http.Request) {
    user := r.Context().Value("user").(string)
    fmt.Fprintf(w, "Hello, %s!", user)
}

func main() {
    http.HandleFunc("/", LoggingMiddleware(AuthMiddleware(MyHandler)))
    http.ListenAndServe(":8080", nil)
}