static long gzippedSize(byte[] data) ctex {
  new JustCountingOutputStream jcos;
  GZIPOutputStream gos = new GZIPOutputStream(jcos);
  gos.write(data, 0, l(data));
  gos.close();
  ret jcos!;
}

static int gzippedSize(S s) {
  ret l(gzipString(s));
}

static long gzippedSize(File f) ctex {
  new JustCountingOutputStream jcos;
  var gos = new GZIPOutputStream(jcos);
  file2stream(f, gos);
  gos.close();
  ret jcos!;
}

Began life as a copy of #1006276