Have nicer 404 errors for covers

album_cover_cache.go

@@ -20,6 +20,12 @@ type AlbumCoverCache struct {
 	TTL time.Duration
 }
 
+type ErrorNotRegistered AlbumID
+
+func (e ErrorNotRegistered) Error() string {
+	return fmt.Sprintf("Cover URL for Album %d is not registered", AlbumID(e))
+}
+
 // NewAlbumCoverCache is creating a new cache at specified location on the fs
 func NewAlbumCoverCache(basepath string, maxRequest uint, window time.Duration) *AlbumCoverCache {
 	res := &AlbumCoverCache{
@@ -37,7 +43,7 @@ func NewAlbumCoverCache(basepath string, maxRequest uint, window time.Duration)
 func (c *AlbumCoverCache) fetch(ID AlbumID) (io.ReadCloser, string, error) {
 	URL, ok := c.URLs[ID]
 	if ok == false {
-		return nil, "", fmt.Errorf("Cover URL for Album %d is not registered", ID)
+		return nil, "", ErrorNotRegistered(ID)
 	}
 	ext := AlbumCoverExt(URL)