Go middleware

server_middleware.go

package main

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

func main() {
	http.Handle("/", logging(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
		w.Write([]byte("Hello"))
	})))

	log.Fatal(http.ListenAndServe(":3000", nil))
}

func logging(next http.Handler) http.Handler {
	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
		t1 := time.Now()
		log.Printf("%s %s <-", r.Method, r.URL.String())
		next.ServeHTTP(w, r)
		log.Printf("%s %s ->", r.Method, r.URL.String())
		t2 := time.Now()
		log.Printf("[%s] %q %v\n", r.Method, r.URL.String(), t2.Sub(t1))
	})
}

Here is the handler interface by the way, https://github.com/golang/go/blob/master/src/net/http/server.go#L81