Bug 1734239 - Implement the CountQueuingStrategy size function. r=smaug

Differential Revision: https://phabricator.services.mozilla.com/D134916

dom/base/nsIGlobalObject.cpp

@@ -134,6 +134,9 @@ void nsIGlobalObject::UnlinkObjectsInGlobal() {
 
   mReportRecords.Clear();
   mReportingObservers.Clear();
+#ifdef MOZ_DOM_STREAMS
+  mCountQueuingStrategySizeFunction = nullptr;
+#endif
 }
 
 void nsIGlobalObject::TraverseObjectsInGlobal(
@@ -149,6 +152,9 @@ void nsIGlobalObject::TraverseObjectsInGlobal(
   nsIGlobalObject* tmp = this;
   NS_IMPL_CYCLE_COLLECTION_TRAVERSE(mReportRecords)
   NS_IMPL_CYCLE_COLLECTION_TRAVERSE(mReportingObservers)
+#ifdef MOZ_DOM_STREAMS
+  NS_IMPL_CYCLE_COLLECTION_TRAVERSE(mCountQueuingStrategySizeFunction)
+#endif
 }
 
 void nsIGlobalObject::AddEventTargetObject(DOMEventTargetHelper* aObject) {
@@ -349,6 +355,18 @@ void nsIGlobalObject::RemoveReportRecords() {
   }
 }
 
+#ifdef MOZ_DOM_STREAMS
+already_AddRefed<mozilla::dom::Function>
+nsIGlobalObject::GetCountQueuingStrategySizeFunction() {
+  return do_AddRef(mCountQueuingStrategySizeFunction);
+}
+
+void nsIGlobalObject::SetCountQueuingStrategySizeFunction(
+    mozilla::dom::Function* aFunction) {
+  mCountQueuingStrategySizeFunction = aFunction;
+}
+#endif
+
 bool nsIGlobalObject::ShouldResistFingerprinting() const {
   return nsContentUtils::ShouldResistFingerprinting();
 }

dom/base/nsIGlobalObject.h

@@ -37,6 +37,7 @@ enum class StorageAccess;
 namespace dom {
 class VoidFunction;
 class DebuggerNotificationManager;
+class Function;
 class Report;
 class ReportBody;
 class ReportingObserver;
@@ -212,6 +213,14 @@ class nsIGlobalObject : public nsISupports,
 
   void RemoveReportRecords();
 
+#ifdef MOZ_DOM_STREAMS
+  // https://streams.spec.whatwg.org/#count-queuing-strategy-size-function
+  // This function is set once by CountQueuingStrategy::GetSize.
+  already_AddRefed<mozilla::dom::Function>
+  GetCountQueuingStrategySizeFunction();
+  void SetCountQueuingStrategySizeFunction(mozilla::dom::Function* aFunction);
+#endif
+
   /**
    * Check whether we should avoid leaking distinguishing information to JS/CSS.
    * https://w3c.github.io/fingerprinting-guidance/
@@ -240,6 +249,11 @@ class nsIGlobalObject : public nsISupports,
   // List of Report objects for ReportingObservers.
   nsTArray<RefPtr<mozilla::dom::ReportingObserver>> mReportingObservers;
   nsTArray<RefPtr<mozilla::dom::Report>> mReportRecords;
+
+#ifdef MOZ_DOM_STREAMS
+  // https://streams.spec.whatwg.org/#count-queuing-strategy-size-function
+  RefPtr<mozilla::dom::Function> mCountQueuingStrategySizeFunction;
+#endif
 };
 
 NS_DEFINE_STATIC_IID_ACCESSOR(nsIGlobalObject, NS_IGLOBALOBJECT_IID)

dom/streams/CountQueuingStrategy.cpp

@@ -5,6 +5,7 @@
  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
 
 #include "mozilla/dom/CountQueuingStrategy.h"
+#include "mozilla/dom/FunctionBinding.h"
 #include "mozilla/dom/QueuingStrategyBinding.h"
 #include "nsCOMPtr.h"
 
@@ -37,5 +38,59 @@ JSObject* CountQueuingStrategy::WrapObject(JSContext* aCx,
   return CountQueuingStrategy_Binding::Wrap(aCx, this, aGivenProto);
 }
 
+// https://streams.spec.whatwg.org/#count-queuing-strategy-size-function
+static bool CountQueuingStrategySize(JSContext* aCx, unsigned aArgc,
+                                     JS::Value* aVp) {
+  JS::CallArgs args = CallArgsFromVp(aArgc, aVp);
+
+  // Step 1.1. Return 1.
+  args.rval().setInt32(1);
+  return true;
+}
+
+// https://streams.spec.whatwg.org/#cqs-size
+already_AddRefed<Function> CountQueuingStrategy::GetSize(ErrorResult& aRv) {
+  // Step 1. Return this's relevant global object's count queuing strategy
+  // size function.
+  if (RefPtr<Function> fun = mGlobal->GetCountQueuingStrategySizeFunction()) {
+    return fun.forget();
+  }
+
+  // Note: Instead of eagerly allocating a size function for every global object
+  // we do it lazily once in this getter.
+  // After this point the steps refer to:
+  // https://streams.spec.whatwg.org/#count-queuing-strategy-size-function.
+
+  AutoJSAPI jsapi;
+  if (!jsapi.Init(mGlobal)) {
+    aRv.ThrowUnknownError("Internal error");
+    return nullptr;
+  }
+  JSContext* cx = jsapi.cx();
+
+  // Step 1. Let steps be the following steps:
+  // Note: See CountQueuingStrategySize instead.
+
+  // Step 2. Let F be
+  // ! CreateBuiltinFunction(steps, 0, "size", « »,
+  //                         globalObject’s relevant Realm).
+  JS::Rooted<JSFunction*> sizeFunction(
+      cx, JS_NewFunction(cx, CountQueuingStrategySize, 0, 0, "size"));
+  if (!sizeFunction) {
+    aRv.StealExceptionFromJSContext(cx);
+    return nullptr;
+  }
+
+  // Step 3. Set globalObject’s count queuing strategy size function to
+  // a Function that represents a reference to F,
+  // with callback context equal to globalObject’s relevant settings object.
+  JS::Rooted<JSObject*> funObj(cx, JS_GetFunctionObject(sizeFunction));
+  JS::Rooted<JSObject*> global(cx, mGlobal->GetGlobalJSObject());
+  RefPtr<Function> function = new Function(cx, funObj, global, mGlobal);
+  mGlobal->SetCountQueuingStrategySizeFunction(function);
+
+  return function.forget();
+}
+
 }  // namespace dom
 }  // namespace mozilla

dom/streams/CountQueuingStrategy.h

@@ -52,7 +52,7 @@ class CountQueuingStrategy final : public nsISupports, public nsWrapperCache {
 
   double HighWaterMark() const { return mHighWaterMark; }
 
-  already_AddRefed<Function> Size() const;
+  already_AddRefed<Function> GetSize(ErrorResult& aRv);
 
  private:
   double mHighWaterMark = 0.0;

dom/webidl/QueuingStrategy.webidl

@@ -16,8 +16,6 @@ interface CountQueuingStrategy {
 
   readonly attribute unrestricted double highWaterMark;
 
-  // This is currently inlined, but will need to be implemented
-  // See Bug 1734239
-  //
-  // readonly attribute Function size;
+  [Throws]
+  readonly attribute Function size;
 };