middleware_option.go

package main

import (
	"encoding/json"
	"fmt"
	"net/http"
)

type Middleware func(http.Handler) http.Handler

func NewHandler(middlewares ...Middleware) func(http.HandlerFunc) http.HandlerFunc {
	return func(final http.HandlerFunc) http.HandlerFunc {
		handler := buildChain(handleFinal(final), middlewares...)
		return handler.ServeHTTP
	}
}

func buildChain(final http.HandlerFunc, middlewares ...Middleware) http.Handler {
	if len(middlewares) == 0 {
		return final
	}
	return middlewares[0](buildChain(final, middlewares[1:]...))
}

func PrintMiddleware(word string) Middleware {
	return func(next http.Handler) http.Handler {
		return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
			fmt.Printf("%s %s %s \n", r.Method, r.URL.Path, word)
			next.ServeHTTP(w, r)
		})
	}
}

func handleFinal(finalHandler http.HandlerFunc) http.HandlerFunc {
	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
		finalHandler(w, r)
	})
}

func healthCheck(w http.ResponseWriter, r *http.Request) {
	renderJson(w, r, map[string]string{"status": "OK"})
}

func hello(w http.ResponseWriter, r *http.Request) {
	renderJson(w, r, map[string]string{"message": "hello"})
}

func main() {
	router := http.NewServeMux()
	router.HandleFunc("/health", NewHandler(
		PrintMiddleware("health1"),
		PrintMiddleware("health2"),
		PrintMiddleware("health3"),
	)(healthCheck))
	router.HandleFunc("/hello", NewHandler(
		PrintMiddleware("hello"),
	)(healthCheck))
	http.ListenAndServe(":8090", router)
}

func renderJson(resp http.ResponseWriter, r *http.Request, obj interface{}) {
	resp.Header().Set("Content-Type", "application/json")
	resp.WriteHeader(200)
	if err := json.NewEncoder(resp).Encode(obj); err != nil {
		http.Error(resp, err.Error(), http.StatusInternalServerError)
	}
}