docs: public List<Integer> getTrackIds() {
          ArrayList<Integer> results = new ArrayList<Integer>(trackCount);
          Enumeration<? extends ZipEntry> entries = zipFile.entries();
          while (entries.hasMoreElements()) {
              ZipEntry entry = entries.nextElement();
              if (entry.getName().startsWith(CACHE_METADATA_ENTRY_PREFIX)) {
                  String idPart = entry.getName().substring(CACHE_METADATA_ENTRY_PREFIX.length());
                  if (idPart.length() > 0) {
                      results.add(Integer.valueOf(idPart));
                  }
              }
          }
  
          return Collections.unmodifiableList(results);
      }