HTTP Middleware (Decorator Pattern)

package main

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

func logging(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 — %s", r.Method, r.URL.Path, time.Since(start))
    })
}

func recoverer(next http.Handler) http.Handler {
    return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
        defer func() {
            if rec := recover(); rec != nil {
                log.Printf("panic: %v", rec)
                http.Error(w, "internal error", http.StatusInternalServerError)
            }
        }()
        next.ServeHTTP(w, r)
    })
}

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

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

    handler := chain(mux, logging, recoverer)
    log.Fatal(http.ListenAndServe(":8080", handler))
}