Bug 1452562 [wpt PR 10348] - Allow range headers to pass through a service worker, a=testonly
authorJake Archibald <jaffathecake@gmail.com>
Wed, 06 Jun 2018 16:35:52 +0000
changeset 422208 8b458f3d30b63afa745527bc31744f4971749224
parent 422207 6424db14b6d5ab082bb7006836003de754ac1f67
child 422209 098ab2cd9e0dbbf21c7a602266bacbc499c59dc1
push id34122
push userebalazs@mozilla.com
push dateMon, 11 Jun 2018 09:37:00 +0000
treeherdermozilla-central@9941eb8c3b29 [default view] [failures only]
perfherder[talos] [build metrics] [platform microbench] (compared to previous push)
reviewerstestonly
bugs1452562, 10348
milestone62.0a1
first release with
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nightly linux64
nightly mac
nightly win32
nightly win64
last release without
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nightly linux64
nightly mac
nightly win32
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Bug 1452562 [wpt PR 10348] - Allow range headers to pass through a service worker, a=testonly Automatic update from web-platform-testsAllow range headers to pass through a service worker (#10348) Tests for https://github.com/whatwg/fetch/pull/560 -- wpt-commits: fb6d16d92af29262b6137b79e61f0c4b136c6ac1 wpt-pr: 10348
testing/web-platform/meta/MANIFEST.json
testing/web-platform/tests/fetch/range/general.any.js
testing/web-platform/tests/fetch/range/partial-script.window.js
testing/web-platform/tests/fetch/range/resources/basic.html
testing/web-platform/tests/fetch/range/resources/long-wav.py
testing/web-platform/tests/fetch/range/resources/partial-script.py
testing/web-platform/tests/fetch/range/resources/range-sw.js
testing/web-platform/tests/fetch/range/resources/stash-take.py
testing/web-platform/tests/fetch/range/resources/utils.js
testing/web-platform/tests/fetch/range/sw.https.window.js
testing/web-platform/tests/service-workers/service-worker/resources/test-helpers.sub.js
--- a/testing/web-platform/meta/MANIFEST.json
+++ b/testing/web-platform/meta/MANIFEST.json
@@ -273611,16 +273611,46 @@
      {}
     ]
    ],
    "fetch/origin/resources/redirect-and-stash.py": [
     [
      {}
     ]
    ],
+   "fetch/range/resources/basic.html": [
+    [
+     {}
+    ]
+   ],
+   "fetch/range/resources/long-wav.py": [
+    [
+     {}
+    ]
+   ],
+   "fetch/range/resources/partial-script.py": [
+    [
+     {}
+    ]
+   ],
+   "fetch/range/resources/range-sw.js": [
+    [
+     {}
+    ]
+   ],
+   "fetch/range/resources/stash-take.py": [
+    [
+     {}
+    ]
+   ],
+   "fetch/range/resources/utils.js": [
+    [
+     {}
+    ]
+   ],
    "fetch/sec-metadata/README.md": [
     [
      {}
     ]
    ],
    "fetch/sec-metadata/resources/echo-as-json.py": [
     [
      {}
@@ -330605,16 +330635,38 @@
      "/fetch/origin/no-cors.any.html",
      {}
     ],
     [
      "/fetch/origin/no-cors.any.worker.html",
      {}
     ]
    ],
+   "fetch/range/general.any.js": [
+    [
+     "/fetch/range/general.any.html",
+     {}
+    ],
+    [
+     "/fetch/range/general.any.worker.html",
+     {}
+    ]
+   ],
+   "fetch/range/partial-script.window.js": [
+    [
+     "/fetch/range/partial-script.window.html",
+     {}
+    ]
+   ],
+   "fetch/range/sw.https.window.js": [
+    [
+     "/fetch/range/sw.https.window.html",
+     {}
+    ]
+   ],
    "fetch/sec-metadata/fetch.tentative.https.sub.html": [
     [
      "/fetch/sec-metadata/fetch.tentative.https.sub.html",
      {}
     ]
    ],
    "fetch/sec-metadata/iframe.tentative.https.sub.html": [
     [
@@ -559760,16 +559812,52 @@
   "fetch/origin/no-cors.any.js": [
    "e9774c1c02bac3833b042c4895733d7bc8b36456",
    "testharness"
   ],
   "fetch/origin/resources/redirect-and-stash.py": [
    "bb002c0d5d4d46f426462f776cff00cf600f5a4a",
    "support"
   ],
+  "fetch/range/general.any.js": [
+   "2c16c0398373fca53ae80aae1107868c8cdeb6b4",
+   "testharness"
+  ],
+  "fetch/range/partial-script.window.js": [
+   "1352080860b8671290919ab0d09cb41f4100763e",
+   "testharness"
+  ],
+  "fetch/range/resources/basic.html": [
+   "51a23151c28992fe062b36914463de216bd55fbe",
+   "support"
+  ],
+  "fetch/range/resources/long-wav.py": [
+   "a9bdaefeb4e9cefd4bb678832d7ffcbe1b3167f7",
+   "support"
+  ],
+  "fetch/range/resources/partial-script.py": [
+   "d74bf301d56ad7d5ae4067e8e27ec544a21aa2ed",
+   "support"
+  ],
+  "fetch/range/resources/range-sw.js": [
+   "1ec66e1dd8bf9a11b058b90e32ca7caab2233d4d",
+   "support"
+  ],
+  "fetch/range/resources/stash-take.py": [
+   "9d29b6276fa690d6acb366bdb4d60a12bc57ea52",
+   "support"
+  ],
+  "fetch/range/resources/utils.js": [
+   "81cc493a76265cc64408fc2d41a67434ec99391a",
+   "support"
+  ],
+  "fetch/range/sw.https.window.js": [
+   "5bf1ebc9ce82990013831f2f7f55589e29a69bde",
+   "testharness"
+  ],
   "fetch/sec-metadata/README.md": [
    "75d58b35c1e5572d02dd3ad90ac65301e35c4bc7",
    "support"
   ],
   "fetch/sec-metadata/fetch.tentative.https.sub.html": [
    "6ce26d3683b78ca74a20b14ccca077cf375d742b",
    "testharness"
   ],
@@ -603481,17 +603569,17 @@
    "31ca62ad01049549f05ec52dda828defcbe2ac6e",
    "support"
   ],
   "service-workers/service-worker/resources/svg-target-reftest-frame.html": [
    "0f7bf8a7cccb1fb4aa5948fb7a684857006b295f",
    "support"
   ],
   "service-workers/service-worker/resources/test-helpers.sub.js": [
-   "74ea529125a5e2c5cd3d350f7c56ae614f82010d",
+   "079d31394903266dddb067f8f4dba5a94e522bdc",
    "support"
   ],
   "service-workers/service-worker/resources/testharness-helpers.js": [
    "15f29256ea90b9c4f91411e570d5dd1979ff73b2",
    "support"
   ],
   "service-workers/service-worker/resources/unregister-controller-page.html": [
    "feae7f538da58d45e38f6f26da5ce6af0c91857f",
new file mode 100644
--- /dev/null
+++ b/testing/web-platform/tests/fetch/range/general.any.js
@@ -0,0 +1,60 @@
+// Helpers that return headers objects with a particular guard
+function headersGuardNone(fill) {
+  if (fill) return new Headers(fill);
+  return new Headers();
+}
+
+function headersGuardResponse(fill) {
+  const opts = {};
+  if (fill) opts.headers = fill;
+  return new Response('', opts).headers;
+}
+
+function headersGuardRequest(fill) {
+  const opts = {};
+  if (fill) opts.headers = fill;
+  return new Request('./', opts).headers;
+}
+
+function headersGuardRequestNoCors(fill) {
+  const opts = { mode: 'no-cors' };
+  if (fill) opts.headers = fill;
+  return new Request('./', opts).headers;
+}
+
+const headerGuardTypes = [
+  ['none', headersGuardNone],
+  ['response', headersGuardResponse],
+  ['request', headersGuardRequest]
+];
+
+for (const [guardType, createHeaders] of headerGuardTypes) {
+  test(() => {
+    // There are three ways to set headers.
+    // Filling, appending, and setting. Test each:
+    let headers = createHeaders({ Range: 'foo' });
+    assert_equals(headers.get('Range'), 'foo');
+
+    headers = createHeaders();
+    headers.append('Range', 'foo');
+    assert_equals(headers.get('Range'), 'foo');
+
+    headers = createHeaders();
+    headers.set('Range', 'foo');
+    assert_equals(headers.get('Range'), 'foo');
+  }, `Range header setting allowed for guard type: ${guardType}`);
+}
+
+test(() => {
+  let headers = headersGuardRequestNoCors({ Range: 'foo' });
+  assert_false(headers.has('Range'));
+
+  headers = headersGuardRequestNoCors();
+  headers.append('Range', 'foo');
+  assert_false(headers.has('Range'));
+
+  headers = headersGuardRequestNoCors();
+  headers.set('Range', 'foo');
+  assert_false(headers.has('Range'));
+}, `Privileged header not allowed for guard type: request-no-cors`);
+
new file mode 100644
--- /dev/null
+++ b/testing/web-platform/tests/fetch/range/partial-script.window.js
@@ -0,0 +1,7 @@
+// META: script=resources/utils.js
+
+// It's weird that browsers do this, but it should continue to work.
+promise_test(async t => {
+  await loadScript('resources/partial-script.py?pretend-offset=90000');
+  assert_true(self.scriptExecuted);
+}, `Script executed from partial response`);
new file mode 100644
--- /dev/null
+++ b/testing/web-platform/tests/fetch/range/resources/basic.html
@@ -0,0 +1,1 @@
+<!DOCTYPE html>
new file mode 100644
--- /dev/null
+++ b/testing/web-platform/tests/fetch/range/resources/long-wav.py
@@ -0,0 +1,111 @@
+"""
+This generates a 30 minute silent wav, and is capable of
+responding to Range requests.
+"""
+import time
+import re
+import struct
+
+
+def create_wav_header(sample_rate, bit_depth, channels, duration):
+    bytes_per_sample = bit_depth / 8
+    block_align = bytes_per_sample * channels
+    byte_rate = sample_rate * block_align
+    sub_chunk_2_size = duration * byte_rate
+
+    data = b''
+    # ChunkID
+    data += b'RIFF'
+    # ChunkSize
+    data += struct.pack('<L', 36 + sub_chunk_2_size)
+    # Format
+    data += b'WAVE'
+    # Subchunk1ID
+    data += b'fmt '
+    # Subchunk1Size
+    data += struct.pack('<L', 16)
+    # AudioFormat
+    data += struct.pack('<H', 1)
+    # NumChannels
+    data += struct.pack('<H', channels)
+    # SampleRate
+    data += struct.pack('<L', sample_rate)
+    # ByteRate
+    data += struct.pack('<L', byte_rate)
+    # BlockAlign
+    data += struct.pack('<H', block_align)
+    # BitsPerSample
+    data += struct.pack('<H', bit_depth)
+    # Subchunk2ID
+    data += b'data'
+    # Subchunk2Size
+    data += struct.pack('<L', sub_chunk_2_size)
+
+    return data
+
+
+def main(request, response):
+    response.headers.set("Content-Type", "audio/wav")
+    response.headers.set("Accept-Ranges", "bytes")
+    response.headers.set("Cache-Control", "no-cache")
+
+    range_header = request.headers.get('Range', '')
+    range_received_key = request.GET.first('range-received-key', '')
+
+    if range_received_key and range_header:
+        # This is later collected using stash-take.py
+        request.stash.put(range_received_key, 'range-header-received', '/fetch/range/')
+
+    # Audio details
+    sample_rate = 8000
+    bit_depth = 8
+    channels = 1
+    duration = 60 * 5
+
+    total_length = (sample_rate * bit_depth * channels * duration) / 8
+    bytes_remaining_to_send = total_length
+    initial_write = ''
+
+    if range_header:
+        response.status = 206
+        start, end = re.search(r'^bytes=(\d*)-(\d*)$', range_header).groups()
+
+        start = int(start)
+        end = int(end) if end else 0
+
+        if end:
+            bytes_remaining_to_send = (end + 1) - start
+        else:
+            bytes_remaining_to_send = total_length - start
+
+        wav_header = create_wav_header(sample_rate, bit_depth, channels, duration)
+
+        if start < len(wav_header):
+            initial_write = wav_header[start:]
+
+            if bytes_remaining_to_send < len(initial_write):
+                initial_write = initial_write[0:bytes_remaining_to_send]
+
+        content_range = "bytes {}-{}/{}".format(start, end or total_length - 1, total_length)
+
+        response.headers.set("Content-Range", content_range)
+    else:
+        initial_write = create_wav_header(sample_rate, bit_depth, channels, duration)
+
+    response.headers.set("Content-Length", bytes_remaining_to_send)
+
+    response.write_status_headers()
+    response.writer.write(initial_write)
+
+    bytes_remaining_to_send -= len(initial_write)
+
+    while bytes_remaining_to_send > 0:
+        if not response.writer.flush():
+            break
+
+        to_send = b'\x00' * min(bytes_remaining_to_send, sample_rate)
+        bytes_remaining_to_send -= len(to_send)
+
+        response.writer.write(to_send)
+        # Throttle the stream
+        time.sleep(0.5)
new file mode 100644
--- /dev/null
+++ b/testing/web-platform/tests/fetch/range/resources/partial-script.py
@@ -0,0 +1,30 @@
+"""
+This generates a partial response containing valid JavaScript.
+"""
+
+
+def main(request, response):
+    require_range = request.GET.first('require-range', '')
+    pretend_offset = int(request.GET.first('pretend-offset', '0'))
+    range_header = request.headers.get('Range', '')
+
+    if require_range and not range_header:
+        response.set_error(412, "Range header required")
+        response.write()
+        return
+
+    response.headers.set("Content-Type", "text/plain")
+    response.headers.set("Accept-Ranges", "bytes")
+    response.headers.set("Cache-Control", "no-cache")
+    response.status = 206
+
+    to_send = 'self.scriptExecuted = true;'
+    length = len(to_send)
+
+    content_range = "bytes {}-{}/{}".format(
+        pretend_offset, pretend_offset + length - 1, pretend_offset + length)
+
+    response.headers.set("Content-Range", content_range)
+    response.headers.set("Content-Length", length)
+
+    response.content = to_send
new file mode 100644
--- /dev/null
+++ b/testing/web-platform/tests/fetch/range/resources/range-sw.js
@@ -0,0 +1,142 @@
+importScripts('/resources/testharness.js');
+
+setup({ explicit_done: true });
+
+function assert_range_request(request, expectedRangeHeader, name) {
+  assert_equals(request.headers.get('Range'), expectedRangeHeader, name);
+}
+
+async function broadcast(msg) {
+  for (const client of await clients.matchAll()) {
+    client.postMessage(msg);
+  }
+}
+
+addEventListener('fetch', event => {
+  /** @type Request */
+  const request = event.request;
+  const url = new URL(request.url);
+  const action = url.searchParams.get('action');
+
+  switch (action) {
+    case 'range-header-filter-test':
+      rangeHeaderFilterTest(request);
+      return;
+    case 'range-header-passthrough-test':
+      rangeHeaderPassthroughTest(event);
+      return;
+    case 'store-ranged-response':
+      storeRangedResponse(event);
+      return;
+    case 'use-stored-ranged-response':
+      useStoredRangeResponse(event);
+      return;
+  }
+});
+
+/**
+ * @param {Request} request
+ */
+function rangeHeaderFilterTest(request) {
+  const rangeValue = request.headers.get('Range');
+
+  test(() => {
+    assert_range_request(new Request(request), rangeValue, `Untampered`);
+    assert_range_request(new Request(request, {}), rangeValue, `Untampered (no init props set)`);
+    assert_range_request(new Request(request, { __foo: 'bar' }), rangeValue, `Untampered (only invalid props set)`);
+    assert_range_request(new Request(request, { mode: 'cors' }), rangeValue, `More permissive mode`);
+    assert_range_request(request.clone(), rangeValue, `Clone`);
+  }, "Range headers correctly preserved");
+
+  test(() => {
+    assert_range_request(new Request(request, { headers: { Range: 'foo' } }), null, `Tampered - range header set`);
+    assert_range_request(new Request(request, { headers: {} }), null, `Tampered - empty headers set`);
+    assert_range_request(new Request(request, { mode: 'no-cors' }), null, `Tampered – mode set`);
+    assert_range_request(new Request(request, { cache: 'no-cache' }), null, `Tampered – cache mode set`);
+  }, "Range headers correctly removed");
+
+  test(() => {
+    let headers;
+
+    headers = new Request(request).headers;
+    headers.delete('does-not-exist');
+    assert_equals(headers.get('Range'), rangeValue, `Preserved if no header actually removed`);
+
+    headers = new Request(request).headers;
+    headers.append('foo', 'bar');
+    assert_equals(headers.get('Range'), rangeValue, `Preserved if silent-failure on append (due to request-no-cors guard)`);
+
+    headers = new Request(request).headers;
+    headers.set('foo', 'bar');
+    assert_equals(headers.get('Range'), rangeValue, `Preserved if silent-failure on set (due to request-no-cors guard)`);
+
+    headers = new Request(request).headers;
+    headers.append('Range', 'foo');
+    assert_equals(headers.get('Range'), rangeValue, `Preserved if silent-failure on append (due to request-no-cors guard)`);
+
+    headers = new Request(request).headers;
+    headers.set('Range', 'foo');
+    assert_equals(headers.get('Range'), rangeValue, `Preserved if silent-failure on set (due to request-no-cors guard)`);
+
+    headers = new Request(request).headers;
+    headers.append('Accept', 'whatever');
+    assert_equals(headers.get('Range'), null, `Stripped if header successfully appended`);
+
+    headers = new Request(request).headers;
+    headers.set('Accept', 'whatever');
+    assert_equals(headers.get('Range'), null, `Stripped if header successfully set`);
+
+    headers = new Request(request).headers;
+    headers.delete('Accept');
+    assert_equals(headers.get('Range'), null, `Stripped if header successfully deleted`);
+
+    headers = new Request(request).headers;
+    headers.delete('Range');
+    assert_equals(headers.get('Range'), null, `Stripped if range header successfully deleted`);
+  }, "Headers correctly filtered");
+
+  done();
+}
+
+function rangeHeaderPassthroughTest(event) {
+  /** @type Request */
+  const request = event.request;
+  const url = new URL(request.url);
+  const key = url.searchParams.get('range-received-key');
+
+  event.waitUntil(new Promise(resolve => {
+    promise_test(async () => {
+      await fetch(event.request);
+      const response = await fetch('stash-take.py?key=' + key);
+      assert_equals(await response.json(), '"range-header-received"');
+      resolve();
+    }, `Include range header in network request`);
+
+    done();
+  }));
+
+  // Just send back any response, it isn't important for the test.
+  event.respondWith(new Response(''));
+}
+
+let storedRangeResponseP;
+
+function storeRangedResponse(event) {
+  /** @type Request */
+  const request = event.request;
+  const id = new URL(request.url).searchParams.get('id');
+
+  storedRangeResponseP = fetch(event.request);
+  broadcast({ id });
+
+  // Just send back any response, it isn't important for the test.
+  event.respondWith(new Response(''));
+}
+
+function useStoredRangeResponse(event) {
+  event.respondWith(async function() {
+    const response = await storedRangeResponseP;
+    if (!response) throw Error("Expected stored range response");
+    return response.clone();
+  }());
+}
new file mode 100644
--- /dev/null
+++ b/testing/web-platform/tests/fetch/range/resources/stash-take.py
@@ -0,0 +1,7 @@
+from wptserve.handlers import json_handler
+
+
+@json_handler
+def main(request, response):
+    key = request.GET.first("key")
+    return request.server.stash.take(key, '/fetch/range/')
new file mode 100644
--- /dev/null
+++ b/testing/web-platform/tests/fetch/range/resources/utils.js
@@ -0,0 +1,9 @@
+function loadScript(url, { doc = document }={}) {
+  return new Promise((resolve, reject) => {
+    const script = doc.createElement('script');
+    script.onload = () => resolve();
+    script.onerror = () => reject(Error("Script load failed"));
+    script.src = url;
+    doc.body.appendChild(script);
+  })
+}
new file mode 100644
--- /dev/null
+++ b/testing/web-platform/tests/fetch/range/sw.https.window.js
@@ -0,0 +1,128 @@
+// META: script=../../../service-workers/service-worker/resources/test-helpers.sub.js
+// META: script=/common/utils.js
+// META: script=/common/get-host-info.sub.js
+// META: script=resources/utils.js
+
+const { REMOTE_HOST } = get_host_info();
+const SCOPE = 'resources/basic.html' + Math.random();
+
+function appendAudio(document, url) {
+  const audio = document.createElement('audio');
+  audio.muted = true;
+  audio.src = url;
+  audio.preload = true;
+  document.body.appendChild(audio);
+}
+
+async function cleanup() {
+  for (const iframe of document.querySelectorAll('.test-iframe')) {
+    iframe.parentNode.removeChild(iframe);
+  }
+
+  const reg = await navigator.serviceWorker.getRegistration(SCOPE);
+  if (reg) await reg.unregister();
+}
+
+async function setupRegistration(t) {
+  await cleanup();
+  const reg = await navigator.serviceWorker.register('resources/range-sw.js', { scope: SCOPE });
+  await wait_for_state(t, reg.installing, 'activated');
+  return reg;
+}
+
+function awaitMessage(obj, id) {
+  return new Promise(resolve => {
+    obj.addEventListener('message', function listener(event) {
+      if (event.data.id !== id) return;
+      obj.removeEventListener('message', listener);
+      resolve();
+    });
+  });
+}
+
+promise_test(async t => {
+  const reg = await setupRegistration(t);
+  const iframe = await with_iframe(SCOPE);
+  const w = iframe.contentWindow;
+
+  // Trigger a cross-origin range request using media
+  const url = new URL('long-wav.py?action=range-header-filter-test', w.location);
+  url.hostname = REMOTE_HOST;
+  appendAudio(w.document, url);
+
+  // See rangeHeaderFilterTest in resources/range-sw.js
+  await fetch_tests_from_worker(reg.active);
+}, `Defer range header filter tests to service worker`);
+
+promise_test(async t => {
+  const reg = await setupRegistration(t);
+  const iframe = await with_iframe(SCOPE);
+  const w = iframe.contentWindow;
+
+  // Trigger a cross-origin range request using media
+  const url = new URL('long-wav.py', w.location);
+  url.searchParams.set('action', 'range-header-passthrough-test');
+  url.searchParams.set('range-received-key', token());
+  url.hostname = REMOTE_HOST;
+  appendAudio(w.document, url);
+
+  // See rangeHeaderPassthroughTest in resources/range-sw.js
+  await fetch_tests_from_worker(reg.active);
+}, `Defer range header passthrough tests to service worker`);
+
+promise_test(async t => {
+  await setupRegistration(t);
+  const iframe = await with_iframe(SCOPE);
+  const w = iframe.contentWindow;
+  const id = Math.random() + '';
+  const storedRangeResponse = awaitMessage(w.navigator.serviceWorker, id);
+
+  // Trigger a cross-origin range request using media
+  const url = new URL('partial-script.py', w.location);
+  url.searchParams.set('require-range', '1');
+  url.searchParams.set('action', 'store-ranged-response');
+  url.searchParams.set('id', id);
+  url.hostname = REMOTE_HOST;
+
+  appendAudio(w.document, url);
+
+  await storedRangeResponse;
+
+  // Fetching should reject
+  const fetchPromise = w.fetch('?action=use-stored-ranged-response', { mode: 'no-cors' });
+  promise_rejects(t, new TypeError(), fetchPromise);
+
+  // Script loading should error too
+  const loadScriptPromise = loadScript('?action=use-stored-ranged-response', { doc: w.document });
+  promise_rejects(t, new Error(), loadScriptPromise);
+
+  await loadScriptPromise.catch(() => {});
+
+  assert_false(!!w.scriptExecuted, `Partial response shouldn't be executed`);
+}, `Ranged response not allowed following no-cors ranged request`);
+
+promise_test(async t => {
+  await setupRegistration(t);
+  const iframe = await with_iframe(SCOPE);
+  const w = iframe.contentWindow;
+  const id = Math.random() + '';
+  const storedRangeResponse = awaitMessage(w.navigator.serviceWorker, id);
+
+  // Trigger a range request using media
+  const url = new URL('partial-script.py', w.location);
+  url.searchParams.set('require-range', '1');
+  url.searchParams.set('action', 'store-ranged-response');
+  url.searchParams.set('id', id);
+
+  appendAudio(w.document, url);
+
+  await storedRangeResponse;
+
+  // This should not throw
+  await w.fetch('?action=use-stored-ranged-response');
+
+  // This shouldn't throw either
+  await loadScript('?action=use-stored-ranged-response', { doc: w.document });
+
+  assert_true(w.scriptExecuted, `Partial response should be executed`);
+}, `Non-opaque ranged response executed`);
--- a/testing/web-platform/tests/service-workers/service-worker/resources/test-helpers.sub.js
+++ b/testing/web-platform/tests/service-workers/service-worker/resources/test-helpers.sub.js
@@ -41,19 +41,24 @@ function unreached_fulfillment(test, pre
 function unreached_rejection(test, prefix) {
   return test.step_func(function(error) {
       var reason = error.message || error.name || error;
       var error_prefix = prefix || 'unexpected rejection';
       assert_unreached(error_prefix + ': ' + reason);
     });
 }
 
-// Adds an iframe to the document and returns a promise that resolves to the
-// iframe when it finishes loading. The caller is responsible for removing the
-// iframe later if needed.
+/**
+ * Adds an iframe to the document and returns a promise that resolves to the
+ * iframe when it finishes loading. The caller is responsible for removing the
+ * iframe later if needed.
+ *
+ * @param {string} url
+ * @returns {HTMLIFrameElement}
+ */
 function with_iframe(url) {
   return new Promise(function(resolve) {
       var frame = document.createElement('iframe');
       frame.className = 'test-iframe';
       frame.src = url;
       frame.onload = function() { resolve(frame); };
       document.body.appendChild(frame);
     });