handlers.go

package main

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

func logHandler(handler http.Handler) http.Handler {
	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
		log.Printf("%s %s\n", r.Method, r.URL)
		handler.ServeHTTP(w, r)
	})
}

func cacheHandler(handler http.Handler) http.Handler {
	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
		r.Header.Del("If-None-Match")
		r.Header.Del("If-Range")
		r.Header.Del("If-Modified-Since")

		w.Header().Set("Cache-Control", "no-cache, no-store, must-revalidate")
		if r.Proto == "HTTP/1.0" {
			w.Header().Set("Pragma", "no-cache")
		}

		handler.ServeHTTP(w, r)
	})
}

func corsHandler(handler http.Handler) http.Handler {
	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
		var origin, method, headers string

		origin = r.Header.Get("Origin")

		if r.Method == "OPTIONS" {
			method = r.Header.Get("Access-Control-Request-Method")
			headers = r.Header.Get("Access-Control-Request-Headers")

			if len(origin) == 0 || len(method) == 0 {
				msg := fmt.Sprintf("%d %s: missing required CORS headers",
						http.StatusBadRequest, http.StatusText(http.StatusBadRequest))
				http.Error(w, msg, http.StatusBadRequest)
				return;
			}
		}

		if len(origin) > 0 {
			w.Header().Add("Vary", "Origin")
			w.Header().Set("Access-Control-Allow-Origin", origin)
			w.Header().Set("Access-Control-Allow-Credentials", "true")
		}

		if len(method) > 0 {
			w.Header().Add("Vary", "Access-Control-Request-Method")
			w.Header().Set("Access-Control-Allow-Methods", method)
		}

		if len(headers) > 0 {
			w.Header().Add("Vary", "Access-Control-Request-Headers")
			w.Header().Set("Access-Control-Allow-Headers", headers)
		}

		if r.Method != "OPTIONS" {
			handler.ServeHTTP(w, r)
		}
	})
}