gecko-dev/content/base/test/bug444546.sjs

const CC = Components.Constructor;
const BinaryInputStream = CC("@mozilla.org/binaryinputstream;1",
                             "nsIBinaryInputStream",
                             "setInputStream");

function handleRequest(request, response)
{
  response.setHeader("Content-Type", "text/plain", false);

  var body = new BinaryInputStream(request.bodyInputStream);

  var avail;
  var bytes = [];
  while ((avail = body.available()) > 0)
    Array.prototype.push.apply(bytes, body.readByteArray(avail));

  var data = String.fromCharCode.apply(null, bytes);
  response.bodyOutputStream.write(data, data.length);
}