Node.js (Express) Style Go Middleware in 40 line of code.

express.go

package main

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

type Handler func(rw http.ResponseWriter, r *http.Request, next http.HandlerFunc)

type stack struct {
	handler Handler
	next    *stack
}

var noop = &stack{func(rw http.ResponseWriter, r *http.Request, next http.HandlerFunc) {}, &stack{}}

func (s stack) ServeHTTP(rw http.ResponseWriter, r *http.Request) {
	s.handler(rw, r, s.next.ServeHTTP)
}

func App(handle Handler) *stack {
	return &stack{handle, noop}
}

func (s *stack) Use(handler Handler) *stack {
	if s.next != noop {
		return s.next.Use(handler)
	}
	s.next = &stack{handler, noop}
	return s
}

func (s *stack) Run(addr string) {
	log.Printf("Listening on: %s\n\n", addr)
	log.Fatal(http.ListenAndServe(addr, s))
}

//Example Usage:
func logger(rw http.ResponseWriter, r *http.Request, next http.HandlerFunc) {
	start := time.Now()
	log.Printf("Started   %s %s", r.Method, r.URL.Path)
	next(rw, r)
	log.Printf("Completed %s %s in %v\n\n", r.Method, r.URL.Path, time.Since(start))
}

// Wrapper for http.Handlers
func Wrap(h http.Handler) Handler {
	return func(rw http.ResponseWriter, r *http.Request, next http.HandlerFunc) {
		h.ServeHTTP(rw, r)
		next(rw, r)
	}
}

func main() {

	fs := http.FileServer(http.Dir("/usr/share/doc"))

	app := App(logger)

	app.Use(Wrap(fs))

	//Oh, and print the useragent IP.
	app.Use(func(rw http.ResponseWriter, r *http.Request, next http.HandlerFunc) {
		log.Printf("Useragent IP  %s", r.RemoteAddr)
		next(rw, r)
	})

	//Now lets run it!
	app.Run(":8080")
	//as 'stack' is a http.Handler, so you can use it like this too.
	//log.Fatal(http.ListenAndServe(":8080", app))
}