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diff --git a/netwerk/test/unit/test_stale-while-revalidate_max-age-0.js b/netwerk/test/unit/test_stale-while-revalidate_max-age-0.js
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+++ b/netwerk/test/unit/test_stale-while-revalidate_max-age-0.js
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+/*
+
+Tests the Cache-control: stale-while-revalidate response directive.
+
+Purpose is to check we perform the background revalidation when max-age=0 but
+the window is set and we hit it.
+
+* Make request #1.
+  - response is from the server and version=1
+  - max-age=0, stale-while-revalidate=9999
+* Switch version of the data on the server and prolong the max-age to not let req #3
+  do a bck reval at the end of the test (prevent leaks/shutdown races.)
+* Make request #2 in 2 seconds (entry should be expired by that time, but fall into
+  the reval window.)
+  - response is from the cache, version=1
+  - a new background request should be made for the data
+* Wait for "http-on-background-revalidation" notifying finish of the background reval.
+* Make request #3.
+  - response is from the cache, version=2
+* Done.
+
+*/
+
+"use strict";
+
+const { HttpServer } = ChromeUtils.import("resource://testing-common/httpd.js");
+
+let max_age;
+let version;
+let generate_response = ver => `response version=${ver}`;
+
+function test_handler(metadata, response) {
+  const originalBody = generate_response(version);
+  response.setHeader("Content-Type", "text/html", false);
+  response.setHeader(
+    "Cache-control",
+    `max-age=${max_age}, stale-while-revalidate=9999`,
+    false
+  );
+  response.setStatusLine(metadata.httpVersion, 200, "OK");
+  response.bodyOutputStream.write(originalBody, originalBody.length);
+}
+
+function make_channel(url) {
+  return NetUtil.newChannel({
+    uri: url,
+    loadUsingSystemPrincipal: true,
+  }).QueryInterface(Ci.nsIHttpChannel);
+}
+
+async function get_response(channel, fromCache) {
+  return new Promise(resolve => {
+    channel.asyncOpen(
+      new ChannelListener((request, buffer, ctx, isFromCache) => {
+        ok(fromCache == isFromCache, `got response from cache = ${fromCache}`);
+        resolve(buffer);
+      })
+    );
+  });
+}
+
+async function sleep(time) {
+  return new Promise(resolve => {
+    do_timeout(time * 1000, resolve);
+  });
+}
+
+async function stop_server(httpserver) {
+  return new Promise(resolve => {
+    httpserver.stop(resolve);
+  });
+}
+
+async function background_reval_promise() {
+  return new Promise(resolve => {
+    Services.obs.addObserver(resolve, "http-on-background-revalidation");
+  });
+}
+
+add_task(async function () {
+  let httpserver = new HttpServer();
+  httpserver.registerPathHandler("/testdir", test_handler);
+  httpserver.start(-1);
+  const PORT = httpserver.identity.primaryPort;
+  const URI = `http://localhost:${PORT}/testdir`;
+
+  let response;
+
+  version = 1;
+  max_age = 0;
+  response = await get_response(make_channel(URI), false);
+  ok(response == generate_response(1), "got response ver 1");
+
+  await sleep(2);
+
+  // must specifically wait for the internal channel to finish the reval to make
+  // the test race-free.
+  let reval_done = background_reval_promise();
+
+  version = 2;
+  max_age = 100;
+  response = await get_response(make_channel(URI), true);
+  ok(response == generate_response(1), "got response ver 1");
+
+  await reval_done;
+
+  response = await get_response(make_channel(URI), true);
+  ok(response == generate_response(2), "got response ver 2");
+
+  await stop_server(httpserver);
+});