pipeline.go

package pipeline

import (
	"fmt"
	"log"
	"net/http"
	"strings"
)

//---- from http_server.go

func WithServerHeader(h http.HandlerFunc) http.HandlerFunc {
	return func(w http.ResponseWriter, r *http.Request) {
		log.Println("--->WithServerHeader()")

		w.Header().Set("Server", "HelloServer v0.0.1")
		h(w, r)
	}
}

func WithAuthCookie(h http.HandlerFunc) http.HandlerFunc {
	return func(w http.ResponseWriter, r *http.Request) {
		log.Println("--->WithAuthCookie()")

		cookie := &http.Cookie{Name: "Auth", Value: "Pass", Path: "/"}
		http.SetCookie(w, cookie)
		h(w, r)
	}
}

func WithBasicAuth(h http.HandlerFunc) http.HandlerFunc {
	return func(w http.ResponseWriter, r *http.Request) {
		log.Println("--->WithBasicAuth()")

		cookie, err := r.Cookie("Auth")

		if err != nil || cookie.Value != "Pass" {
			w.WriteHeader(http.StatusForbidden)
			return
		}
		h(w, r)
	}
}

func WithDebugLog(h http.HandlerFunc) http.HandlerFunc {
	return func(w http.ResponseWriter, r *http.Request) {
		log.Println("--->WithDebugLog")
		_ = r.ParseForm()

		log.Println(r.Form)
		log.Println("path", r.URL.Path)
		log.Println("scheme", r.URL.Scheme)
		log.Println(r.Form["url_long"])

		for k, v := range r.Form {
			log.Println("key:", k)
			log.Println("val:", strings.Join(v, ""))
		}
		h(w, r)
	}
}

func hello(w http.ResponseWriter, r *http.Request) {
	log.Printf("Recieved Request %s from %s\n", r.URL.Path, r.RemoteAddr)
	_, _ = fmt.Fprintf(w, "Hello, World! "+r.URL.Path)
}

// HttpHandlerDecorator is key
type HttpHandlerDecorator func(http.HandlerFunc) http.HandlerFunc

func Handler(h http.HandlerFunc, decors ...HttpHandlerDecorator) http.HandlerFunc {
	for i := range decors {
		decor := decors[len(decors)-1-i] // iterate in reverse
		h = decor(h)
	}
	return h
}

func Run() {
	// verbose
	http.HandleFunc("/v1/hello", WithServerHeader(WithAuthCookie(hello)))
	http.HandleFunc("/v2/hello", WithServerHeader(WithBasicAuth(hello)))
	http.HandleFunc("/v3/hello", WithServerHeader(WithBasicAuth(WithDebugLog(hello))))

	// elegant now !!
	http.HandleFunc("/v4/hello",
		Handler(hello, WithServerHeader, WithBasicAuth, WithDebugLog),
	)
}