middleware pattern go

main.go

package main

import (
	"log"
	"net/http"

	"github.com/gorilla/mux"
)

// FooList handles listing foos
func FooList(w http.ResponseWriter, req *http.Request) {
	w.WriteHeader(200)
	response := "OK"
	log.Println(response)
	w.Write([]byte(response))
}

// Decorator for http.HandlerFunc
type Decorator func(fn http.HandlerFunc) http.HandlerFunc

// Logger middleware
func Logger(s string) Decorator {
	return func(fn http.HandlerFunc) http.HandlerFunc {
		return func(w http.ResponseWriter, req *http.Request) {
			log.Println(s)
			fn.ServeHTTP(w, req)
		}
	}
}

// Authorize checks Authorization header for a given token
func Authorize(token string) Decorator {
	return func(fn http.HandlerFunc) http.HandlerFunc {
		return func(w http.ResponseWriter, req *http.Request) {
			log.Println("Checking authorization")

			// Check if the token matches one of the Authorization values
			for _, val := range req.Header["Authorization"] {
				if token == val {
					fn.ServeHTTP(w, req)
					return
				}
			}

			// No matches, req is unauthorized
			w.WriteHeader(401)
			w.Write([]byte("Unauthorized"))
		}
	}
}

// Decorate applies decorations to a http.Handler
func Decorate(h http.HandlerFunc, decorators ...Decorator) http.HandlerFunc {
	for _, decorator := range decorators {
		h = decorator(h)
	}
	return h
}

func main() {
	router := mux.NewRouter().StrictSlash(true)
	// FooList is the end handler, Authorize & Logger are middleware applied in reverse order
	router.HandleFunc("/foos", Decorate(FooList, Authorize("penguin"), Logger("GET List of Foos"))).Methods("GET")
	log.Fatal(http.ListenAndServe(":8080", router))
}