Bug 1390465: Load all subtitles in RFP. r=tjr

This patch targets non-js mode. By fetching everything, the website can't tell what language is being used.

Trying to protect js enabled mode would be impossible as websites can just use a custom player and record usage as they wish.

Differential Revision: https://phabricator.services.mozilla.com/D223636

dom/html/HTMLTrackElement.cpp

@@ -93,7 +93,8 @@ class WindowDestroyObserver final : public nsIObserver {
       NS_ENSURE_SUCCESS(rv, rv);
       if (innerID == mInnerID) {
         if (mTrackElement) {
-          mTrackElement->CancelChannelAndListener();
+          // Window is being destroyed, cancel without checking for RFP.
+          mTrackElement->CancelChannelAndListener(false);
         }
         UnRegisterWindowDestroyObserver();
       }
@@ -128,7 +129,8 @@ HTMLTrackElement::~HTMLTrackElement() {
   if (mWindowDestroyObserver) {
     mWindowDestroyObserver->UnRegisterWindowDestroyObserver();
   }
-  CancelChannelAndListener();
+  // Track element is being destroyed, cancel without checking for RFP.
+  CancelChannelAndListener(false);
 }
 
 NS_IMPL_ELEMENT_CLONE(HTMLTrackElement)
@@ -250,11 +252,18 @@ void HTMLTrackElement::MaybeDispatchLoadResource() {
 
   // step2, if the text track's text track mode is not set to one of hidden or
   // showing, then return.
-  if (mTrack->Mode() == TextTrackMode::Disabled) {
+  bool resistFingerprinting = ShouldResistFingerprinting(RFPTarget::WebVTT);
+  if (mTrack->Mode() == TextTrackMode::Disabled && !resistFingerprinting) {
     LOG("Do not load resource for disable track");
     return;
   }
 
+  // We need to do this check in order to prevent
+  // HonorUserPreferencesForTrackSelection from loading the text track twice.
+  if (resistFingerprinting && ReadyState() == TextTrackReadyState::Loading) {
+    return;
+  }
+
   // step3, if the text track's track element does not have a media element as a
   // parent, return.
   if (!mMediaParent) {
@@ -294,7 +303,8 @@ void HTMLTrackElement::LoadResource(RefPtr<WebVTTListener>&& aWebVTTListener) {
   NS_ENSURE_TRUE_VOID(NS_SUCCEEDED(rv));
   LOG("Trying to load from src=%s", NS_ConvertUTF16toUTF8(src).get());
 
-  CancelChannelAndListener();
+  // Prevent canceling the channel and listener if RFP is enabled.
+  CancelChannelAndListener(true);
 
   // According to
   // https://www.w3.org/TR/html5/embedded-content-0.html#sourcing-out-of-band-text-tracks
@@ -470,7 +480,11 @@ void HTMLTrackElement::DispatchTrustedEvent(const nsAString& aName) {
                                        Cancelable::eNo);
 }
 
-void HTMLTrackElement::CancelChannelAndListener() {
+void HTMLTrackElement::CancelChannelAndListener(bool aCheckRFP) {
+  if (aCheckRFP && ShouldResistFingerprinting(RFPTarget::WebVTT)) {
+    return;
+  }
+
   if (mChannel) {
     mChannel->CancelWithReason(NS_BINDING_ABORTED,
                                "HTMLTrackElement::CancelChannelAndListener"_ns);
@@ -484,6 +498,15 @@ void HTMLTrackElement::CancelChannelAndListener() {
   }
 }
 
+bool HTMLTrackElement::ShouldResistFingerprinting(RFPTarget aRfpTarget) {
+  Document* doc = OwnerDoc();
+  if (!doc) {
+    return nsContentUtils::ShouldResistFingerprinting("Null document",
+                                                      aRfpTarget);
+  }
+  return doc->ShouldResistFingerprinting(aRfpTarget);
+}
+
 void HTMLTrackElement::AfterSetAttr(int32_t aNameSpaceID, nsAtom* aName,
                                     const nsAttrValue* aValue,
                                     const nsAttrValue* aOldValue,

dom/html/HTMLTrackElement.h

@@ -98,7 +98,9 @@ class HTMLTrackElement final : public nsGenericHTMLElement {
   void DispatchTrustedEvent(const nsAString& aName);
   void DispatchTestEvent(const nsAString& aName);
 
-  void CancelChannelAndListener();
+  void CancelChannelAndListener(bool aCheckRFP);
+
+  bool ShouldResistFingerprinting(RFPTarget aRfpTarget);
 
   // Only load resource for the non-disabled track with media parent.
   void MaybeDispatchLoadResource();

dom/media/webvtt/WebVTTListener.cpp

@@ -114,7 +114,8 @@ WebVTTListener::OnStopRequest(nsIRequest* aRequest, nsresult aStatus) {
     mElement->SetReadyState(TextTrackReadyState::Loaded);
   }
 
-  mElement->CancelChannelAndListener();
+  // Prevent canceling the channel and listener if RFP is enabled.
+  mElement->CancelChannelAndListener(true);
 
   return aStatus;
 }

dom/media/webvtt/test/mochitest/basicvtt-server.sjs

@@ -0,0 +1,124 @@
+// This file is a simple "server" for test_webvtt_resistfingerprinting.html
+
+// You can request a VTT file by setting the `request` parameter to `vtt` and
+// providing an `id` parameter. Id parameter is used to track how many times
+// a specific test has requested the file. Please don't use the same id for
+// multiple tests.
+
+// You can also request the number of times a specific test has requested the
+// file by setting the `request` parameter to `count` and providing an `id`
+// parameter.
+
+const vtt = `WEBVTT
+REGION
+id:testOne lines:2 width:30%
+REGION
+id:testTwo lines:4 width:20%
+
+1
+00:00.500 --> 00:00.700 region:testOne
+This
+
+2
+00:01.200 --> 00:02.400 region:testTwo
+Is
+
+2.5
+00:02.000 --> 00:03.500 region:testOne
+(Over here?!)
+
+3
+00:02.710 --> 00:02.910
+A
+
+4
+00:03.217 --> 00:03.989
+Test
+
+5
+00:03.217 --> 00:03.989
+And more!
+`;
+
+// stolen from server-stream-download.sjs# and they stole it from file_blocked_script.sjs
+function setGlobalState(data, key) {
+  const x = {
+    data,
+    QueryInterface(_iid) {
+      return this;
+    },
+  };
+  x.wrappedJSObject = x;
+  setObjectState(key, x);
+}
+
+function getGlobalState(key) {
+  let data;
+  getObjectState(key, function (x) {
+    data = x && x.wrappedJSObject.data;
+  });
+  return data;
+}
+
+const requestCounter = (() => {
+  const keyPrefix = "vtt-request-counter-";
+
+  return {
+    recordRequest(id) {
+      const key = keyPrefix + id;
+      const count = getGlobalState(key) || 0;
+      setGlobalState(count + 1, key);
+    },
+    getRequestCount(id) {
+      const key = keyPrefix + id;
+      return getGlobalState(key) || 0;
+    },
+  };
+})();
+
+// We need this for test-verify jobs. It runs the test
+// multiple times and we need to know how many times
+// the test has been run because global state is not
+// reset between runs.
+const iterationCounter = (() => {
+  const keyPrefix = "vtt-request-iteration-counter-";
+
+  return {
+    recordIteration() {
+      const count = getGlobalState(keyPrefix) || 0;
+      setGlobalState(count + 1, keyPrefix);
+    },
+    getIterationCount() {
+      return getGlobalState(keyPrefix) || 0;
+    },
+  };
+})();
+
+function handleRequest(aRequest, aResponse) {
+  aResponse.setHeader("Access-Control-Allow-Origin", "*", false);
+
+  const params = aRequest.queryString
+    .split("&")
+    .map(command => command.split("="))
+    .reduce((acc, [key, value]) => {
+      acc[key] = value;
+      return acc;
+    }, {});
+
+  if (params.request === "vtt") {
+    requestCounter.recordRequest(params.id);
+    aResponse.setStatusLine(aRequest.httpVersion, 200);
+    aResponse.setHeader("Content-Type", "text/vtt", false);
+    aResponse.write(vtt);
+  } else if (params.request === "count") {
+    aResponse.setStatusLine(aRequest.httpVersion, 200);
+    aResponse.write(requestCounter.getRequestCount(params.id));
+  } else if (params.request === "newIteration") {
+    iterationCounter.recordIteration();
+    aResponse.setStatusLine(aRequest.httpVersion, 200);
+    aResponse.write(iterationCounter.getIterationCount());
+  } else {
+    aResponse.setStatusLine(aRequest.httpVersion, 400);
+    aResponse.write(aRequest.queryString);
+  }
+}

dom/media/webvtt/test/mochitest/mochitest.toml

@@ -72,6 +72,12 @@ skip-if = ["true"]
 
 ["test_webvtt_positionalign.html"]
 
+["test_webvtt_resistfingerprinting.html"]
+support-files = [
+  "basicvtt-server.sjs",
+]
+run-sequentially = "An extension having the same id is installed/uninstalled in different tests"
+
 ["test_webvtt_seeking.html"]
 
 ["test_webvtt_update_display_after_adding_or_removing_cue.html"]

dom/media/webvtt/test/mochitest/test_webvtt_resistfingerprinting.html

@@ -0,0 +1,76 @@
+<!DOCTYPE HTML>
+<html>
+<head>
+  <meta charset='utf-8'>
+  <title>WebVTT: ResistFingerprinting</title>
+  <script src="/tests/SimpleTest/SimpleTest.js"></script>
+  <link rel="stylesheet" type="text/css" href="/tests/SimpleTest/test.css"/>
+</head>
+<body>
+<div id="content">
+</div>
+<template id="video">
+  <video width="600" height="400" controls onloadeddata="handleOnLoadedData()">
+    <source src="gizmo.mp4" type="video/mp4">
+    <track label="VTT1" kind="subtitles" srclang="en" src="basicvtt-server.sjs?request=vtt&id=test_webvtt_resistfingerprinting.html" />
+    <track label="VTT2" kind="subtitles" srclang="es" src="basicvtt-server.sjs?request=vtt&id=test_webvtt_resistfingerprinting.html" />
+    <track label="VTT3" kind="subtitles" srclang="tr" src="basicvtt-server.sjs?request=vtt&id=test_webvtt_resistfingerprinting.html" default />
+  </video>
+</template>
+<script class="testbody" type="text/javascript">
+SimpleTest.waitForExplicitFinish();
+SimpleTest.requestFlakyTimeout("Need to wait for all VTT files to be loaded");
+
+let iteration = "0";
+async function startTest() {
+  await SpecialPowers.pushPrefEnv({
+    "set": [
+      ["privacy.resistFingerprinting", true]
+    ]
+  });
+
+  iteration = await fetch("basicvtt-server.sjs?request=newIteration")
+    .then(response => response.text());
+
+  const video = document.getElementById("video").content.cloneNode(true);
+  video.querySelectorAll("track").forEach(track => {
+    track.src = track.src + iteration;
+  });
+  document.getElementById("content").appendChild(video);
+}
+
+async function handleOnLoadedData() {
+  // Wait for 5 minutes at most
+  for (let i = 0; i < 5 * 60; i++) {
+    const shouldEnd = await fetch("basicvtt-server.sjs?request=count&id=test_webvtt_resistfingerprinting.html" + iteration)
+      .then(response => response.text())
+      .then(text => {
+        info("Number of VTT files loaded: " + text);
+        const num = +text;
+        if (num === 3) {
+          ok(true, "All VTT files are loaded");
+          return true
+        }
+        if (num > 3) {
+          ok(false, "Too many VTT files are loaded");
+          return true;
+        }
+        return false;
+      }).catch(error => {
+        ok(false, "Failed to fetch count: " + error);
+        return true;
+      });
+    if (shouldEnd) {
+      break;
+    }
+    await new Promise(resolve => setTimeout(resolve, 1000));
+  }
+
+  await SpecialPowers.popPrefEnv();
+  SimpleTest.finish();
+}
+
+onload = startTest;
+</script>
+</body>
+</html>

toolkit/components/resistfingerprinting/RFPTargets.inc

@@ -93,6 +93,7 @@ ITEM_VALUE(SiteSpecificZoom,            1llu << 60)
 // Are font visibility restrictions applied when resolving a CSS <generic-family>?
 // (This may block the fonts selected in Preferences from actually being used.)
 ITEM_VALUE(FontVisibilityRestrictGenerics, 1llu << 61)
+ITEM_VALUE(WebVTT,                      1llu << 62)
 
 // !!! Don't forget to update kDefaultFingerprintingProtections in nsRFPService.cpp
 // if necessary.