fune/dom/base/test/bug457746.sjs

function handleRequest(request, response) {
  response.setHeader("Content-Type", "text/plain; charset=ISO-8859-1", false);
  const body = [0xc1];
  var bos = Components.classes[
    "@mozilla.org/binaryoutputstream;1"
  ].createInstance(Components.interfaces.nsIBinaryOutputStream);
  bos.setOutputStream(response.bodyOutputStream);

  bos.writeByteArray(body);
}