sS limitedStruct(int limit, O o) {
  var baos = new ByteArrayOutputStream();
  var out = new LimitedOutputStream(baos, limit);
  var writer = printWriter(out);
  try {
    structureToPrintWriter(o, writer);
  } catch e {
    writer.close();
    fail("Struct exceeded limit of " + n2(limit) + " bytes: " + fromUtf8(baos.toByteArray()));
  }
  writer.close();
  ret fromUtf8(baos.toByteArray());
}