Send a transparent pixel if no favicon was found

This can be changed with the `?error=true` parameter.  Sending a
transparent pixel should look better and make caching possible.

go/favicon/favicon.go

	"github.com/golang/groupcache/lru"
)
var transparentPixelPNG = []byte{
	0x89, 0x50, 0x4e, 0x47, 0x0d, 0x0a, 0x1a, 0x0a, 0x00, 0x00, 0x00, 0x0d,
	0x49, 0x48, 0x44, 0x52, 0x00, 0x00, 0x00, 0x01, 0x00, 0x00, 0x00, 0x01,
	0x01, 0x03, 0x00, 0x00, 0x00, 0x25, 0xdb, 0x56, 0xca, 0x00, 0x00, 0x00,
	0x03, 0x50, 0x4c, 0x54, 0x45, 0x00, 0x00, 0x00, 0xa7, 0x7a, 0x3d, 0xda,
	0x00, 0x00, 0x00, 0x01, 0x74, 0x52, 0x4e, 0x53, 0x00, 0x40, 0xe6, 0xd8,
	0x66, 0x00, 0x00, 0x00, 0x0a, 0x49, 0x44, 0x41, 0x54, 0x08, 0xd7, 0x63,
	0x60, 0x00, 0x00, 0x00, 0x02, 0x00, 0x01, 0xe2, 0x21, 0xbc, 0x33, 0x00,
	0x00, 0x00, 0x00, 0x49, 0x45, 0x4e, 0x44, 0xae, 0x42, 0x60, 0x82,
}
const transparentPixelMD5 = "71a50dbba44c78128b221b7df7bb51f1"
var port = flag.Int("p", 8080, "port [8080]")
var cacheSize = flag.Int("s", 10000, "cache size [10000]")
var debug = flag.Bool("debug", false, "Print out debug info")
	favicon, err := GetFaviconCached(url)
	if err != nil {
		fmt.Printf("Error: '%s': %s\n", url, err)
		w.WriteHeader(http.StatusNotFound)
		w.Write([]byte(fmt.Sprint(err)))
		if r.URL.Query().Get("error") != "" {
			w.WriteHeader(http.StatusNotFound)
			w.Write([]byte(fmt.Sprint(err)))
		} else {
			sendBytes(w, r, transparentPixelPNG, transparentPixelMD5)
		}
		return
	}
	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)))
		if r.URL.Query().Get("error") != "" {
			w.WriteHeader(http.StatusNotFound)
			w.Write([]byte(fmt.Sprint(err)))
		} else {
			sendBytes(w, r, transparentPixelPNG, transparentPixelMD5)
		}
		return
	}
	sendBytes(w, r, image, hash)
}
func sendBytes(w http.ResponseWriter, r *http.Request, data []byte, hash string) {
	w.Header().Set("ETag", hash)
	ifNoneMatch := r.Header.Get("If-None-Match")
		return
	}
	w.Header().Set("Content-Length", fmt.Sprintf("%d", len(image)))
	w.Write(image)
	w.Header().Set("Content-Length", fmt.Sprintf("%d", len(data)))
	w.Write(data)
}
func GetImageCached(u string) ([]byte, string, error) {