XMLHttpRequest/access-control-basic-allow-access-control-origin-header-data-url.htm

<!DOCTYPE html>
<html>
  <head>
    <title>Tests that cross-origin access is granted to null-origin embedded iframe</title>
    <script src="/resources/testharness.js"></script>
    <script src="/resources/testharnessreport.js"></script>
    <script src="/common/get-host-info.sub.js"></script>
  </head>
  <body>
    <script type="text/javascript">
const url = get_host_info().HTTP_REMOTE_ORIGIN + "/XMLHttpRequest/resources/access-control-origin-header.py";
async_test(function(test) {
  window.addEventListener("message", test.step_func(function(evt) {
    if (evt.data == "ready") {
      document.getElementById("frame").contentWindow.postMessage(url, "*");
    } else {
      assert_equals(evt.data, "PASS: Cross-domain access allowed.\nHTTP_ORIGIN: null");
      test.done();
    }
  }), false);
}, "Access granted to null-origin iframe");
    </script>
    <iframe id="frame" src='data:text/html,
    <script>
(function() {
  parent.postMessage("ready", "*");
  window.addEventListener("message", function(evt) {
    try {
      const url = evt.data;
      const xhr = new XMLHttpRequest;

      xhr.open("GET", url, false);
      xhr.send();

      parent.postMessage(xhr.responseText, "*");
    } catch(e) {
      parent.postMessage(e.message, "*");
    }
  });
})();
    </script>'>
  </body>
</html>