Never save a downloaded song outside the download location

app/src/main/java/de/qspool/clementineremote/backend/downloader/ClementineSongDownloader.java

@@ -401,14 +401,25 @@ String buildRelativeDir(ResponseSongFileChunk chunk) {
     }
 
     private static void appendDir(StringBuilder sb, String name) {
-        String dir = Utilities.removeInvalidFileCharacters(name).trim();
+        String dir = safeName(name).trim();
         if (!dir.isEmpty()) {
             sb.append(dir).append('/');
         }
     }
 
+    /** The song's file name, or its title if that leaves nothing. */
     static String buildFileName(ResponseSongFileChunk chunk) {
-        return Utilities.removeInvalidFileCharacters(chunk.getSongMetadata().getFilename());
+        String name = safeName(chunk.getSongMetadata().getFilename());
+        return name.isEmpty() ? safeName(chunk.getSongMetadata().getTitle()) : name;
+    }
+
+    /**
+     * [name] without the characters file names can't have. A name of only dots, such as "..", is
+     * dropped too, so no song is saved outside the download location.
+     */
+    private static String safeName(String name) {
+        String safe = Utilities.removeInvalidFileCharacters(name);
+        return safe.trim().matches("\\.*") ? "" : safe;
     }
 
     public DownloadItem getItem() {

app/src/test/java/de/qspool/clementineremote/backend/downloader/DownloadStorageTest.java

@@ -199,6 +199,21 @@ public void emptyTagsDoNotMakeEmptyFolders() {
         assertEquals("", downloader.buildRelativeDir(chunk("", "", "")));
     }
 
+    @Test
+    public void savesNothingOutsideTheDownloadLocation() {
+        ClementineSongDownloader downloader = new ClementineSongDownloader();
+        downloader.setCreateArtistDir(true);
+        downloader.setCreateAlbumDir(true);
+        downloader.setIsPlaylist(true, "...");
+        downloader.setCreatePlaylistDir(true);
+        assertEquals("", downloader.buildRelativeDir(chunk("..", "", " .. ")));
+
+        ResponseSongFileChunk chunk = ResponseSongFileChunk.newBuilder()
+                .setSongMetadata(SongMetadata.newBuilder().setFilename("..").setTitle("Aria"))
+                .build();
+        assertEquals("Aria", ClementineSongDownloader.buildFileName(chunk));
+    }
+
     @Test
     public void unknownFileTypesAreSavedAsAudio() {
         assertEquals("audio/mpeg", MediaStoreDownloadStorage.mimeType("song"));