Handle empty cover art ID in subsonic API

core/artwork.go

@@ -41,9 +41,13 @@ type artwork struct {
 }
 
 func (a *artwork) Get(ctx context.Context, id string, size int) (io.ReadCloser, error) {
-	artID, err := model.ParseArtworkID(id)
-	if err != nil {
-		return nil, errors.New("invalid ID")
+	var artID model.ArtworkID
+	var err error
+	if id != "" {
+		artID, err = model.ParseArtworkID(id)
+		if err != nil {
+			return nil, errors.New("invalid ID")
+		}
 	}
 
 	key := &artworkKey{a: a, artID: artID, size: size}

core/artwork_internal_test.go

@@ -41,6 +41,14 @@ var _ = Describe("Artwork", func() {
 		aw = NewArtwork(ds, cache).(*artwork)
 	})
 
+	Context("Empty ID", func() {
+		It("returns placeholder if album is not in the DB", func() {
+			_, path, err := aw.get(context.Background(), model.ArtworkID{}, 0)
+			Expect(err).ToNot(HaveOccurred())
+			Expect(path).To(Equal(consts.PlaceholderAlbumArt))
+		})
+	})
+
 	Context("Albums", func() {
 		Context("ID not found", func() {
 			It("returns placeholder if album is not in the DB", func() {

server/subsonic/media_retrieval.go

@@ -51,7 +51,7 @@ func (api *Router) getPlaceHolderAvatar(w http.ResponseWriter, r *http.Request)
 }
 
 func (api *Router) GetCoverArt(w http.ResponseWriter, r *http.Request) (*responses.Subsonic, error) {
-	id := utils.ParamStringDefault(r, "id", "non-existent")
+	id := utils.ParamString(r, "id")
 	size := utils.ParamInt(r, "size", 0)
 
 	w.Header().Set("cache-control", "public, max-age=315360000")