Easy Middleware in Go

main.go

package main

import (
	"net/http"
	"time"
	"log"
)

func main() {
	dh := DispatchHandler{}
	dh.Attach(DontCache)
	dh.Attach(Timer)
	dh.Finalize(Router)

	h := &http.Server{Addr: ":80", Handler: dh}
	h.ListenAndServe()
}

// Dispatch Handler

type DispatchHandler struct {
	stack []func(next func(w http.ResponseWriter, r *http.Request)) func(w http.ResponseWriter, r *http.Request)
	final func(w http.ResponseWriter, r *http.Request)
}
func (h *DispatchHandler) Attach(m func(func(w http.ResponseWriter, r *http.Request)) func(w http.ResponseWriter, r *http.Request)) {
	h.stack = append(h.stack, m)
}
func (h *DispatchHandler) Finalize(final func(w http.ResponseWriter, r *http.Request)) {
	h.final = final
	for i := len(h.stack); i > 0; i-- {
		h.final = h.stack[i-1](h.final)
	}
}
func (h DispatchHandler) ServeHTTP(w http.ResponseWriter, r *http.Request) {
	h.final(w, r)
}

// Middleware

func DontCache(next func(w http.ResponseWriter, r *http.Request)) func(w http.ResponseWriter, r *http.Request) {
	return func(w http.ResponseWriter, r *http.Request) {
		w.Header().Set("Cache-Control", "max-age=0, no-cache, must-revalidate")
		next(w, r)
	}
}

func Timer(next func(w http.ResponseWriter, r *http.Request)) func(w http.ResponseWriter, r *http.Request) {
	return func(w http.ResponseWriter, r *http.Request) {
		start := time.Now()
		next(w, r)
		log.Printf("%d %s", time.Since(start).Nanoseconds() / 1e3, r.URL.Path)
	}
}

// Router

var routes = map[string]func(http.ResponseWriter, *http.Request){
	"/":      IndexHandler,
	"/hello": HelloHandler,
	"/world": WorldHandler,
	"/panic": PanicHandler,
}
func Router(w http.ResponseWriter, r *http.Request) {
	if handle, ok := routes[r.URL.Path]; ok {
		handle(w, r)
	} else {
		http.Error(w, "Not Found : "+r.URL.Path, 404)
	}
}
func IndexHandler(w http.ResponseWriter, r *http.Request) {
	http.Error(w, "Hello, World!", 200)
}
func HelloHandler(w http.ResponseWriter, r *http.Request) {
	http.Error(w, "Hello", 200)
}
func WorldHandler(w http.ResponseWriter, r *http.Request) {
	http.Error(w, "World", 200)
}
func PanicHandler(w http.ResponseWriter, r *http.Request) {
	log.Panic("REM WAS RIGHT")
}