A couple of middleware http.Handler functions for Go

middleware.go

// A couple of middleware http.Handler functions (scroll down).

// EXAMPLE USAGE:

http.HandleFunc("/", RequestHome)
http.Handle("/s/", Cacher(168*time.Hour, http.StripPrefix("/s/", http.FileServer(http.Dir("static")))))
http.Handle("/favicon.ico", FileWithCache("static/favicon.ico", 168*time.Hour))

if err := http.ListenAndServe(":8080", Logger(http.DefaultServeMux)); err != nil {
  log.Fatalf("http.ListenAndServe: %v", err)
}

// IMPLEMENTATION:

// Cacher returns a public Cache-Control header for all requests.
func Cacher(duration time.Duration, h http.Handler) http.Handler {
	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
		header := w.Header()
		header.Set("Cache-Control", fmt.Sprintf("public, max-age=%d", int(duration.Seconds())))
		header.Set("Vary", "Accept-Encoding")
		h.ServeHTTP(w, r)
	})
}

func FileWithCache(path string, duration time.Duration) http.Handler {
	return Cacher(duration, http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
		http.ServeFile(w, r, path)
	}))
}

// Logger logs incoming requests, including response status.
func Logger(h http.Handler) http.Handler {
	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
		info := fmt.Sprintf("%s %s %s", r.Method, r.URL, r.Proto)
		o := &responseObserver{ResponseWriter: w}
		h.ServeHTTP(o, r)
		log.Printf("%s %q %d %d %q %q",
			r.RemoteAddr,
			info,
			o.status,
			o.written,
			r.Referer(),
			r.UserAgent())
	})
}

// Spies on http.ResponseWriter (used by Logger).
type responseObserver struct {
	http.ResponseWriter
	status      int
	written     int64
	wroteHeader bool
}

func (o *responseObserver) Write(p []byte) (n int, err error) {
	if !o.wroteHeader {
		o.WriteHeader(http.StatusOK)
	}
	n, err = o.ResponseWriter.Write(p)
	o.written += int64(n)
	return
}

func (o *responseObserver) WriteHeader(code int) {
	o.ResponseWriter.WriteHeader(code)
	if o.wroteHeader {
		return
	}
	o.wroteHeader = true
	o.status = code
}