Go HTTP Middleware Chain

package main

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

type Middleware func(http.Handler) http.Handler

func Chain(h http.Handler, middlewares ...Middleware) http.Handler {
	for i := len(middlewares) - 1; i >= 0; i-- {
		h = middlewares[i](h)
	}
	return h
}

func Logger(next http.Handler) http.Handler {
	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
		start := time.Now()
		next.ServeHTTP(w, r)
		log.Printf("%s %s %v", r.Method, r.URL.Path, time.Since(start))
	})
}

func CORS(next http.Handler) http.Handler {
	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
		w.Header().Set("Access-Control-Allow-Origin", "*")
		w.Header().Set("Access-Control-Allow-Methods", "GET,POST,PUT,DELETE,OPTIONS")
		if r.Method == http.MethodOptions {
			w.WriteHeader(http.StatusNoContent)
			return
		}
		next.ServeHTTP(w, r)
	})
}

func RequireAuth(next http.Handler) http.Handler {
	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
		token := r.Header.Get("Authorization")
		if token == "" {
			http.Error(w, "unauthorized", http.StatusUnauthorized)
			return
		}
		next.ServeHTTP(w, r)
	})
}

func main() {
	mux := http.NewServeMux()
	mux.HandleFunc("/api/data", func(w http.ResponseWriter, r *http.Request) {
		w.Write([]byte(`{"ok":true}`))
	})

	handler := Chain(mux, Logger, CORS, RequireAuth)
	http.ListenAndServe(":8080", handler)
}