Bug 1562021 - part3 : cancel old VTT listener when we start a new load. r=jya,baku

When we start a new load, all previous data fetching from the previous listener and all state changing applied to track element should be ignored.

Therefore, we add a new method `Cancel()` which owner of the listener should call when we would like to discard current listener.

Differential Revision: https://phabricator.services.mozilla.com/D36407

--HG--
extra : moz-landing-system : lando

dom/html/HTMLTrackElement.cpp

@@ -299,9 +299,15 @@ void HTMLTrackElement::LoadResource(RefPtr<WebVTTListener>&& aWebVTTListener) {
 
   if (mChannel) {
     mChannel->Cancel(NS_BINDING_ABORTED);
+    mChannel->SetNotificationCallbacks(nullptr);
     mChannel = nullptr;
   }
 
+  if (mListener) {
+    mListener->Cancel();
+    mListener = nullptr;
+  }
+
   // According to
   // https://www.w3.org/TR/html5/embedded-content-0.html#sourcing-out-of-band-text-tracks
   //

dom/media/WebVTTListener.cpp

@@ -63,6 +63,9 @@ WebVTTListener::GetInterface(const nsIID& aIID, void** aResult) {
 }
 
 nsresult WebVTTListener::LoadResource() {
+  if (IsCanceled()) {
+    return NS_OK;
+  }
   // Exit if we failed to create the WebVTTParserWrapper (vtt.jsm)
   NS_ENSURE_SUCCESS(mParserWrapperError, mParserWrapperError);
 
@@ -74,6 +77,9 @@ NS_IMETHODIMP
 WebVTTListener::AsyncOnChannelRedirect(nsIChannel* aOldChannel,
                                        nsIChannel* aNewChannel, uint32_t aFlags,
                                        nsIAsyncVerifyRedirectCallback* cb) {
+  if (IsCanceled()) {
+    return NS_OK;
+  }
   if (mElement) {
     mElement->OnChannelRedirect(aOldChannel, aNewChannel, aFlags);
   }
@@ -83,12 +89,20 @@ WebVTTListener::AsyncOnChannelRedirect(nsIChannel* aOldChannel,
 
 NS_IMETHODIMP
 WebVTTListener::OnStartRequest(nsIRequest* aRequest) {
+  if (IsCanceled()) {
+    return NS_OK;
+  }
+
   LOG("OnStartRequest");
   return NS_OK;
 }
 
 NS_IMETHODIMP
 WebVTTListener::OnStopRequest(nsIRequest* aRequest, nsresult aStatus) {
+  if (IsCanceled()) {
+    return NS_OK;
+  }
+
   LOG("OnStopRequest");
   if (NS_FAILED(aStatus)) {
     LOG("Got error status");
@@ -111,6 +125,7 @@ nsresult WebVTTListener::ParseChunk(nsIInputStream* aInStream, void* aClosure,
                                     uint32_t* aWriteCount) {
   nsCString buffer(aFromSegment, aCount);
   WebVTTListener* listener = static_cast<WebVTTListener*>(aClosure);
+  MOZ_ASSERT(!listener->IsCanceled());
 
   if (NS_FAILED(listener->mParserWrapper->Parse(buffer))) {
     LOG_WIHTOUT_ADDRESS(
@@ -127,6 +142,10 @@ nsresult WebVTTListener::ParseChunk(nsIInputStream* aInStream, void* aClosure,
 NS_IMETHODIMP
 WebVTTListener::OnDataAvailable(nsIRequest* aRequest, nsIInputStream* aStream,
                                 uint64_t aOffset, uint32_t aCount) {
+  if (IsCanceled()) {
+    return NS_OK;
+  }
+
   LOG("OnDataAvailable");
   uint32_t count = aCount;
   while (count > 0) {
@@ -144,6 +163,7 @@ WebVTTListener::OnDataAvailable(nsIRequest* aRequest, nsIInputStream* aStream,
 
 NS_IMETHODIMP
 WebVTTListener::OnCue(JS::Handle<JS::Value> aCue, JSContext* aCx) {
+  MOZ_ASSERT(!IsCanceled());
   if (!aCue.isObject()) {
     return NS_ERROR_FAILURE;
   }
@@ -161,12 +181,14 @@ WebVTTListener::OnCue(JS::Handle<JS::Value> aCue, JSContext* aCx) {
 
 NS_IMETHODIMP
 WebVTTListener::OnRegion(JS::Handle<JS::Value> aRegion, JSContext* aCx) {
+  MOZ_ASSERT(!IsCanceled());
   // Nothing for this callback to do.
   return NS_OK;
 }
 
 NS_IMETHODIMP
 WebVTTListener::OnParsingError(int32_t errorCode, JSContext* cx) {
+  MOZ_ASSERT(!IsCanceled());
   // We only care about files that have a bad WebVTT file signature right now
   // as that means the file failed to load.
   if (errorCode == ErrorCodes::BadSignature) {
@@ -176,5 +198,16 @@ WebVTTListener::OnParsingError(int32_t errorCode, JSContext* cx) {
   return NS_OK;
 }
 
+bool WebVTTListener::IsCanceled() const { return mCancel; }
+
+void WebVTTListener::Cancel() {
+  MOZ_ASSERT(!IsCanceled(), "Do not cancel canceled listener again!");
+  LOG("Cancel listen to channel's response.");
+  mCancel = true;
+  mParserWrapper->Cancel();
+  mParserWrapper = nullptr;
+  mElement = nullptr;
+}
+
 }  // namespace dom
 }  // namespace mozilla

dom/media/WebVTTListener.h

@@ -42,6 +42,14 @@ class WebVTTListener final : public nsIWebVTTListener,
    */
   nsresult LoadResource();
 
+  /**
+   * When this listener is not going to be used anymore, its owner should take
+   * a responsibility to call `Cancel()` to prevent this listener making any
+   * changes for the track element.
+   */
+  bool IsCanceled() const;
+  void Cancel();
+
  private:
   ~WebVTTListener();
 
@@ -54,6 +62,7 @@ class WebVTTListener final : public nsIWebVTTListener,
   RefPtr<HTMLTrackElement> mElement;
   nsCOMPtr<nsIWebVTTParserWrapper> mParserWrapper;
   nsresult mParserWrapperError;
+  bool mCancel = false;
 };
 
 }  // namespace dom

dom/media/webvtt/WebVTTParserWrapper.jsm

@@ -43,6 +43,12 @@ WebVTTParserWrapper.prototype =
     };
   },
 
+  cancel: function() {
+    this.parser.oncue = null;
+    this.parser.onregion = null;
+    this.parser.onparsingerror = null;
+  },
+
   convertCueToDOMTree: function(window, cue)
   {
     return WebVTT.convertCueToDOMTree(window, cue.text);

dom/media/webvtt/nsIWebVTTParserWrapper.idl

@@ -52,6 +52,11 @@ interface nsIWebVTTParserWrapper : nsISupports
    */
   void watch(in nsIWebVTTListener callback);
 
+  /**
+   * Cancel watching notifications which parser would send.
+   */
+  void cancel();
+
   /**
    * Convert the text content of a WebVTT cue to a document fragment so that
    * we can display it on the page.