decorator.go

package main

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

type HandlerWrapper func(http.ResponseWriter, *http.Request)

func (h HandlerWrapper) ServeHTTP(w http.ResponseWriter, r *http.Request) {
	h(w, r)
}

type Decorator func(http.Handler) http.Handler

func Logging(l *log.Logger) Decorator {
	return func(h http.Handler) http.Handler {
		return HandlerWrapper(func(w http.ResponseWriter, r *http.Request) {
			l.Println(r.URL.String(), r.RemoteAddr)
			h.ServeHTTP(w, r)
		})
	}
}

func Header(key, name string) Decorator {
	return func(h http.Handler) http.Handler {
		return HandlerWrapper(func(w http.ResponseWriter, r *http.Request) {
			w.Header().Add(key, name)
			h.ServeHTTP(w, r)
		})
	}
}

func BuildDecorator(h http.Handler, decrorator ...Decorator) http.Handler {
	for _, de := range decrorator {
		h = de(h)
	}
	return h
}

func HandleQuery(w http.ResponseWriter, r *http.Request) {
	w.Write([]byte("Hello Decorator"))
}

func main() {
	logger := log.New(os.Stdout, "Test", log.Ldate)
	http.Handle("/query", BuildDecorator(
		HandlerWrapper(HandleQuery),
		Logging(logger),
		Header("TTT", "VVV")))
	http.ListenAndServe(":9990", nil)
}