Send cache headers with the proxied images

go/favicon/favicon.go

package main
import (
	"crypto/md5"
	"errors"
	"flag"
	"fmt"
var lock sync.RWMutex
var imageCache *lru.Cache
var imageHashes *lru.Cache
var imageLock sync.RWMutex
func main() {
	faviconCache = lru.New(*cacheSize)
	imageCache = lru.New(*cacheSize)
	imageHashes = lru.New(*cacheSize)
	http.HandleFunc("/favicon", HandleGetFavicon)
	http.HandleFunc("/favicon_proxy", HandleProxy)
}
func HandleProxy(w http.ResponseWriter, r *http.Request) {
	w.Header().Set("Cache-Control", "max-age=2419200")
	url := r.URL.Query()["url"][0]
	favicon, err := GetFaviconCached(url)
	if err != nil {
		return
	}
	image, err := GetImageCached(favicon)
	image, hash, err := GetImageCached(favicon)
	if err != nil {
		fmt.Printf("Error: '%s': %s\n", url, err)
		w.WriteHeader(http.StatusNotFound)
		w.Write([]byte(fmt.Sprint(err)))
		return
	}
	w.Header().Set("ETag", hash)
	ifNoneMatch := r.Header.Get("If-None-Match")
	if ifNoneMatch != "" && hash == ifNoneMatch {
		w.WriteHeader(http.StatusNotModified)
		return
	}
	w.Header().Set("Content-Length", fmt.Sprintf("%d", len(image)))
	w.Write(image)
}
func GetImageCached(u string) ([]byte, error) {
func GetImageCached(u string) ([]byte, string, error) {
	imageLock.RLock()
	image, cached := imageCache.Get(u)
	hash, _ := imageHashes.Get(u)
	imageLock.RUnlock()
	if cached {
		return image.([]byte), nil
		return image.([]byte), hash.(string), nil
	}
	resp, err := http.Get(u)
	if err != nil {
		return nil, err
		return nil, "", err
	}
	defer resp.Body.Close()
	imageData, err := ioutil.ReadAll(resp.Body)
	if err != nil {
		return nil, err
		return nil, "", err
	}
	imageHash := fmt.Sprintf("%x", md5.Sum(imageData))
	imageLock.Lock()
	imageCache.Add(u, imageData)
	imageHashes.Add(u, imageHash)
	imageLock.Unlock()
	return imageData, nil
	return imageData, imageHash, nil
}