Bug 1888634 - Disallow captureStream with canvas transferred to DOM w…

…orker. This behaviour has yet to be defined by the spec and/or WPT, see: w3c/mediacapture-fromelement#65 w3c/mediacapture-extensions#26 web-platform-tests/wpt#21102 Differential Revision: https://phabricator.services.mozilla.com/D207582
aosmond · Apr 16, 2024 · 73aa2d6 · 73aa2d6
1 parent a62a8fc
commit 73aa2d6
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diff --git a/dom/canvas/OffscreenCanvas.cpp b/dom/canvas/OffscreenCanvas.cpp
@@ -358,6 +358,21 @@ UniquePtr<OffscreenCanvasCloneData> OffscreenCanvas::ToCloneData(
  return nullptr;
  }
 
+ // Check if we are using HTMLCanvasElement::captureStream. This is not
+ // defined by the spec yet, so it is better to fail now than implement
+ // something not compliant:
+ // https:/w3c/mediacapture-fromelement/issues/65
+ // https:/w3c/mediacapture-extensions/pull/26
+ // https:/web-platform-tests/wpt/issues/21102
+ if (mDisplay && NS_WARN_IF(mDisplay->UsingElementCaptureStream())) {
+ ErrorResult rv;
+ rv.ThrowNotSupportedError(
+ "Cannot transfer OffscreenCanvas bound to element using "
+ "captureStream.");
+ MOZ_ALWAYS_TRUE(rv.MaybeSetPendingException(aCx));
+ return nullptr;
+ }
+
  auto cloneData = MakeUnique<OffscreenCanvasCloneData>(
  mDisplay, mWidth, mHeight, mCompositorBackendType, mTextureType,
  mNeutered, mIsWriteOnly, mExpandedReader);

diff --git a/dom/canvas/OffscreenCanvasDisplayHelper.cpp b/dom/canvas/OffscreenCanvasDisplayHelper.cpp
@@ -61,6 +61,22 @@ void OffscreenCanvasDisplayHelper::DestroyCanvas() {
  mWorkerRef = nullptr;
 }
 
+bool OffscreenCanvasDisplayHelper::CanElementCaptureStream() const {
+ MutexAutoLock lock(mMutex);
+ return !!mWorkerRef;
+}
+
+bool OffscreenCanvasDisplayHelper::UsingElementCaptureStream() const {
+ MutexAutoLock lock(mMutex);
+
+ if (NS_WARN_IF(!NS_IsMainThread())) {
+ MOZ_ASSERT_UNREACHABLE("Should not call off main-thread!");
+ return !!mCanvasElement;
+ }
+
+ return mCanvasElement && mCanvasElement->UsingCaptureStream();
+}
+
 CanvasContextType OffscreenCanvasDisplayHelper::GetContextType() const {
  MutexAutoLock lock(mMutex);
  return mType;

diff --git a/dom/canvas/OffscreenCanvasDisplayHelper.h b/dom/canvas/OffscreenCanvasDisplayHelper.h
@@ -57,6 +57,9 @@ class OffscreenCanvasDisplayHelper final {
  void DestroyCanvas();
  void DestroyElement();
 
+ bool CanElementCaptureStream() const;
+ bool UsingElementCaptureStream() const;
+
  already_AddRefed<mozilla::gfx::SourceSurface> GetSurfaceSnapshot();
  already_AddRefed<mozilla::layers::Image> GetAsImage();
  UniquePtr<uint8_t[]> GetImageBuffer(int32_t* aOutFormat,

diff --git a/dom/html/HTMLCanvasElement.cpp b/dom/html/HTMLCanvasElement.cpp
@@ -857,6 +857,20 @@ already_AddRefed<CanvasCaptureMediaStream> HTMLCanvasElement::CaptureStream(
  return nullptr;
  }
 
+ // Check if we transferred the OffscreenCanvas to a DOM worker. This is not
+ // defined by the spec yet, so it is better to fail now than implement
+ // something not compliant:
+ // https:/w3c/mediacapture-fromelement/issues/65
+ // https:/w3c/mediacapture-extensions/pull/26
+ // https:/web-platform-tests/wpt/issues/21102
+ if (mOffscreenDisplay &&
+ NS_WARN_IF(!mOffscreenDisplay->CanElementCaptureStream())) {
+ aRv.ThrowNotSupportedError(
+ "Capture stream not supported when OffscreenCanvas transferred to "
+ "worker");
+ return nullptr;
+ }
+
  auto stream = MakeRefPtr<CanvasCaptureMediaStream>(window, this);
 
  nsCOMPtr<nsIPrincipal> principal = NodePrincipal();

diff --git a/dom/html/HTMLCanvasElement.h b/dom/html/HTMLCanvasElement.h
@@ -356,6 +356,8 @@ class HTMLCanvasElement final : public nsGenericHTMLElement,
 
  layers::ImageContainer* GetImageContainer() const { return mImageContainer; }
 
+ bool UsingCaptureStream() const { return !!mRequestedFrameRefreshObserver; }
+
  protected:
  bool mResetLayer;
  bool mMaybeModified; // we fetched the context, so we may have written to the