From 518cc7ad584693a4f00be28c8200c33363950a07 Mon Sep 17 00:00:00 2001
From: Andrew Osmond <aosmond@mozilla.com>
Date: Wed, 16 Aug 2023 12:06:34 +0000
Subject: [PATCH] Bug 1848875 - Throw InvalidStateError when cloning
 OffscreenCanvas with context. r=gfx-reviewers,lsalzman

This patch makes us follow the standard and pass WPT tests regarding the
cloning of OffscreenCanvas with a context. It also makes us throw a less
generic message when attempting to clone an OffscreenCanvas that has
already been cloned/transferred to a worker.

Differential Revision: https://phabricator.services.mozilla.com/D186265
---
 dom/base/StructuredCloneHolder.cpp            |  7 ++---
 dom/canvas/OffscreenCanvas.cpp                | 26 ++++++++++++++++---
 dom/canvas/OffscreenCanvas.h                  |  3 ++-
 .../offscreencanvas.transferrable.html.ini    |  3 ---
 .../offscreencanvas.transferrable.w.html.ini  |  8 ------
 5 files changed, 28 insertions(+), 19 deletions(-)
 delete mode 100644 testing/web-platform/meta/html/canvas/offscreen/manual/the-offscreen-canvas/offscreencanvas.transferrable.html.ini
 delete mode 100644 testing/web-platform/meta/html/canvas/offscreen/manual/the-offscreen-canvas/offscreencanvas.transferrable.w.html.ini

diff --git a/dom/base/StructuredCloneHolder.cpp b/dom/base/StructuredCloneHolder.cpp
index aa6af050b478..8040ad057b00 100644
--- a/dom/base/StructuredCloneHolder.cpp
+++ b/dom/base/StructuredCloneHolder.cpp
@@ -1472,16 +1472,17 @@ StructuredCloneHolder::CustomWriteTransferHandler(
       if (NS_SUCCEEDED(rv)) {
         MOZ_ASSERT(canvas);
 
-        if (!canvas->MayNeuter()) {
+        UniquePtr<OffscreenCanvasCloneData> clonedCanvas =
+            canvas->ToCloneData(aCx);
+        if (!clonedCanvas) {
           return false;
         }
 
         *aExtraData = 0;
         *aTag = SCTAG_DOM_CANVAS;
-        *aContent = canvas->ToCloneData();
+        *aContent = clonedCanvas.release();
         MOZ_ASSERT(*aContent);
         *aOwnership = JS::SCTAG_TMO_CUSTOM;
-        canvas->SetNeutered();
 
         return true;
       }
diff --git a/dom/canvas/OffscreenCanvas.cpp b/dom/canvas/OffscreenCanvas.cpp
index df8fc96cb9f0..09e58fedff8c 100644
--- a/dom/canvas/OffscreenCanvas.cpp
+++ b/dom/canvas/OffscreenCanvas.cpp
@@ -305,10 +305,28 @@ void OffscreenCanvas::CommitFrameToCompositor() {
   mDisplay->CommitFrameToCompositor(mCurrentContext, mTextureType, update);
 }
 
-OffscreenCanvasCloneData* OffscreenCanvas::ToCloneData() {
-  return new OffscreenCanvasCloneData(mDisplay, mWidth, mHeight,
-                                      mCompositorBackendType, mTextureType,
-                                      mNeutered, mIsWriteOnly, mExpandedReader);
+UniquePtr<OffscreenCanvasCloneData> OffscreenCanvas::ToCloneData(
+    JSContext* aCx) {
+  if (NS_WARN_IF(mNeutered)) {
+    ErrorResult rv;
+    rv.ThrowDataCloneError(
+        "Cannot clone placeholder canvas that is already transferred.");
+    MOZ_ALWAYS_TRUE(rv.MaybeSetPendingException(aCx));
+    return nullptr;
+  }
+
+  if (NS_WARN_IF(mCurrentContext)) {
+    ErrorResult rv;
+    rv.ThrowInvalidStateError("Cannot clone canvas with context.");
+    MOZ_ALWAYS_TRUE(rv.MaybeSetPendingException(aCx));
+    return nullptr;
+  }
+
+  auto cloneData = MakeUnique<OffscreenCanvasCloneData>(
+      mDisplay, mWidth, mHeight, mCompositorBackendType, mTextureType,
+      mNeutered, mIsWriteOnly, mExpandedReader);
+  SetNeutered();
+  return cloneData;
 }
 
 already_AddRefed<ImageBitmap> OffscreenCanvas::TransferToImageBitmap(
diff --git a/dom/canvas/OffscreenCanvas.h b/dom/canvas/OffscreenCanvas.h
index 30f4ea5940e8..0e1fc682379c 100644
--- a/dom/canvas/OffscreenCanvas.h
+++ b/dom/canvas/OffscreenCanvas.h
@@ -15,6 +15,7 @@
 #include "mozilla/layers/LayersTypes.h"
 #include "mozilla/Maybe.h"
 #include "mozilla/RefPtr.h"
+#include "mozilla/UniquePtr.h"
 #include "nsCycleCollectionParticipant.h"
 
 struct JSContext;
@@ -124,7 +125,7 @@ class OffscreenCanvas final : public DOMEventTargetHelper,
   // on worker thread.
   static bool PrefEnabledOnWorkerThread(JSContext* aCx, JSObject* aObj);
 
-  OffscreenCanvasCloneData* ToCloneData();
+  UniquePtr<OffscreenCanvasCloneData> ToCloneData(JSContext* aCx);
 
   void UpdateDisplayData(const OffscreenCanvasDisplayData& aData);
 
diff --git a/testing/web-platform/meta/html/canvas/offscreen/manual/the-offscreen-canvas/offscreencanvas.transferrable.html.ini b/testing/web-platform/meta/html/canvas/offscreen/manual/the-offscreen-canvas/offscreencanvas.transferrable.html.ini
deleted file mode 100644
index 2269d23a1e8b..000000000000
--- a/testing/web-platform/meta/html/canvas/offscreen/manual/the-offscreen-canvas/offscreencanvas.transferrable.html.ini
+++ /dev/null
@@ -1,3 +0,0 @@
-[offscreencanvas.transferrable.html]
-  [Test that transfer an OffscreenCanvas that already have a 2d context throws exception.]
-    expected: FAIL
diff --git a/testing/web-platform/meta/html/canvas/offscreen/manual/the-offscreen-canvas/offscreencanvas.transferrable.w.html.ini b/testing/web-platform/meta/html/canvas/offscreen/manual/the-offscreen-canvas/offscreencanvas.transferrable.w.html.ini
deleted file mode 100644
index 1c6cb7cd8eb8..000000000000
--- a/testing/web-platform/meta/html/canvas/offscreen/manual/the-offscreen-canvas/offscreencanvas.transferrable.w.html.ini
+++ /dev/null
@@ -1,8 +0,0 @@
-[offscreencanvas.transferrable.w.html]
-  expected:
-    if (os == "linux") and not debug and fission: [OK, CRASH]
-  [Test that transfer an OffscreenCanvas that has a webgl context throws exception in a worker.]
-    expected: FAIL
-
-  [Test that transfer an OffscreenCanvas that has a 2d context throws exception in a worker.]
-    expected: FAIL