static new ThreadLocal<Bool> smartZipCompressionLevel_on;

static AutoCloseable smartZipCompressionLevel(ZipOutputStream zip, File f) {
  ret smartZipCompressionLevel(zip, fileName(f));
}

static AutoCloseable smartZipCompressionLevel(final ZipOutputStream zip, S fileName) {
  if (!isTrue(smartZipCompressionLevel_on!)) null;
  int level = Deflater.DEFAULT_COMPRESSION;
  if (isImageFileName(fileName) || eqicOneOf(fileExtension(fileName), ".zip", ".jar", ".gz", ".bin")) // assume .bin is a jar snippet or some such
    level = Deflater.NO_COMPRESSION;
  zip.setLevel(level);
  ret autoCloseable { zip.setLevel(Deflater.DEFAULT_COMPRESSION); };
}