<!DOCTYPE html>
<meta charset="utf-8">
<title>Tests Stale While Revalidate works for images</title>
<script src="/resources/testharness.js"></script>
<script src="/resources/testharnessreport.js"></script>
<script src="/common/utils.js"></script>
<body>
<!--
Use a child document to load the second stale image into because
an image loaded into the same document will skip cache-control headers.
See: https://html.spec.whatwg.org/#the-list-of-available-images
-->
<iframe id="child1" srcdoc=""></iframe>
<iframe id="child2" srcdoc=""></iframe>
<script>

var request_token = token();
let image_src = "resources/stale-image.py?token=" + request_token;

let loadImage = async (document) => {
  let img = document.createElement("img");
  img.src = image_src;
  let loaded = new Promise(r => img.onload = r);
  document.body.appendChild(img);
  await loaded;
  return img;
};

promise_test(async t => {
  await new Promise(r => window.onload = r);

  let img1 = await loadImage(document);
  assert_equals(img1.width, 16, "(initial version loaded)");

  let img2 = await loadImage(child1.contentDocument);
  assert_equals(img2.width, 16, "(stale version loaded)");

  // Query the server again and again. At some point it must have received the
  // revalidation request. We poll, because we don't know when the revalidation
  // will occur.
  while(true) {
    await new Promise(r => step_timeout(r, 25));
    let response = await fetch(image_src + "&query");
    let count = response.headers.get("Count");
    if (count == '2')
      break;
  }

  let img3 = await loadImage(child2.contentDocument);
  assert_equals(img3.width, 256, "(revalidated version loaded)");

}, 'Cache returns stale resource');

</script>
</body>
