onmessage = function(event) {
  var xhr = new XMLHttpRequest();
  xhr.onreadystatechange = function () {
    if (xhr.readyState !== 4) {
      return;
    }
    parent.postMessage(xhr.responseText, "*");
  };
  xhr.open('POST', location.href, true);
  xhr.setRequestHeader('Content-Type', 'application/json');
  var json;
  try {
    json = JSON.stringify(event.data);
  } catch(e) {}
  xhr.send(json);
};