The Tor Browser: dom/bindings/CallbackObject.h@97036ab72558 (annotated)

dom/bindings/CallbackObject.h@97036ab72558 (annotated)

dom/bindings/CallbackObject.h

Tue, 06 Jan 2015 21:39:09 +0100

author: Michael Schloh von Bennewitz <michael@schloh.com>
date: Tue, 06 Jan 2015 21:39:09 +0100
branch: TOR_BUG_9701
changeset 8: 97036ab72558
permissions: -rw-r--r--

Conditionally force memory storage according to privacy.thirdparty.isolate;
This solves Tor bug #9701, complying with disk avoidance documented in
https://www.torproject.org/projects/torbrowser/design/#disk-avoidance.

 /* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
 /* vim:set ts=2 sw=2 sts=2 et cindent: */
 /* This Source Code Form is subject to the terms of the Mozilla Public
  * License, v. 2.0. If a copy of the MPL was not distributed with this
  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
 /**
  * A common base class for representing WebIDL callback function and
  * callback interface types in C++.
  *
  * This class implements common functionality like lifetime
  * management, initialization with the JS object, and setup of the
  * call environment.  Subclasses are responsible for providing methods
  * that do the call into JS as needed.
  */
 #ifndef mozilla_dom_CallbackObject_h
 #define mozilla_dom_CallbackObject_h
 #include "nsISupports.h"
 #include "nsISupportsImpl.h"
 #include "nsCycleCollectionParticipant.h"
 #include "jswrapper.h"
 #include "mozilla/Assertions.h"
 #include "mozilla/ErrorResult.h"
 #include "mozilla/HoldDropJSObjects.h"
 #include "mozilla/MemoryReporting.h"
 #include "mozilla/dom/ScriptSettings.h"
 #include "nsContentUtils.h"
 #include "nsWrapperCache.h"
 #include "nsJSEnvironment.h"
 #include "xpcpublic.h"
 namespace mozilla {
 namespace dom {
 #define DOM_CALLBACKOBJECT_IID \
 { 0xbe74c190, 0x6d76, 0x4991, \
  { 0x84, 0xb9, 0x65, 0x06, 0x99, 0xe6, 0x93, 0x2b } }
 class CallbackObject : public nsISupports
 {
 public:
   NS_DECLARE_STATIC_IID_ACCESSOR(DOM_CALLBACKOBJECT_IID)
   NS_DECL_CYCLE_COLLECTING_ISUPPORTS
   NS_DECL_CYCLE_COLLECTION_SCRIPT_HOLDER_CLASS(CallbackObject)
   // The caller may pass a global object which will act as an override for the
   // incumbent script settings object when the callback is invoked (overriding
   // the entry point computed from aCallback). If no override is required, the
   // caller should pass null.
   explicit CallbackObject(JS::Handle<JSObject*> aCallback, nsIGlobalObject *aIncumbentGlobal)
   {
     Init(aCallback, aIncumbentGlobal);
   }
   virtual ~CallbackObject()
   {
     DropJSObjects();
   }
   JS::Handle<JSObject*> Callback() const
   {
     JS::ExposeObjectToActiveJS(mCallback);
     return CallbackPreserveColor();
   }
   /*
    * This getter does not change the color of the JSObject meaning that the
    * object returned is not guaranteed to be kept alive past the next CC.
    *
    * This should only be called if you are certain that the return value won't
    * be passed into a JS API function and that it won't be stored without being
    * rooted (or otherwise signaling the stored value to the CC).
    */
   JS::Handle<JSObject*> CallbackPreserveColor() const
   {
     // Calling fromMarkedLocation() is safe because we trace our mCallback, and
     // because the value of mCallback cannot change after if has been set.
     return JS::Handle<JSObject*>::fromMarkedLocation(mCallback.address());
   }
   nsIGlobalObject* IncumbentGlobalOrNull() const
   {
     return mIncumbentGlobal;
   }
   enum ExceptionHandling {
     // Report any exception and don't throw it to the caller code.
     eReportExceptions,
     // Throw an exception to the caller code if the thrown exception is a
     // binding object for a DOMError from the caller's scope, otherwise report
     // it.
     eRethrowContentExceptions,
     // Throw any exception to the caller code.
     eRethrowExceptions
   };
   size_t SizeOfIncludingThis(mozilla::MallocSizeOf aMallocSizeOf) const
   {
     return aMallocSizeOf(this);
   }
 protected:
   explicit CallbackObject(CallbackObject* aCallbackObject)
   {
     Init(aCallbackObject->mCallback, aCallbackObject->mIncumbentGlobal);
   }
   bool operator==(const CallbackObject& aOther) const
   {
     JSObject* thisObj =
       js::UncheckedUnwrap(CallbackPreserveColor());
     JSObject* otherObj =
       js::UncheckedUnwrap(aOther.CallbackPreserveColor());
     return thisObj == otherObj;
   }
 private:
   inline void Init(JSObject* aCallback, nsIGlobalObject* aIncumbentGlobal)
   {
     MOZ_ASSERT(aCallback && !mCallback);
     // Set script objects before we hold, on the off chance that a GC could
     // somehow happen in there... (which would be pretty odd, granted).
     mCallback = aCallback;
     if (aIncumbentGlobal) {
       mIncumbentGlobal = aIncumbentGlobal;
       mIncumbentJSGlobal = aIncumbentGlobal->GetGlobalJSObject();
     }
     mozilla::HoldJSObjects(this);
   }
   CallbackObject(const CallbackObject&) MOZ_DELETE;
   CallbackObject& operator =(const CallbackObject&) MOZ_DELETE;
 protected:
   void DropJSObjects()
   {
     MOZ_ASSERT_IF(mIncumbentJSGlobal, mCallback);
     if (mCallback) {
       mCallback = nullptr;
       mIncumbentJSGlobal = nullptr;
       mozilla::DropJSObjects(this);
     }
   }
   JS::Heap<JSObject*> mCallback;
   // Ideally, we'd just hold a reference to the nsIGlobalObject, since that's
   // what we need to pass to AutoIncumbentScript. Unfortunately, that doesn't
   // hold the actual JS global alive. So we maintain an additional pointer to
   // the JS global itself so that we can trace it.
   //
   // At some point we should consider trying to make native globals hold their
   // scripted global alive, at which point we can get rid of the duplication
   // here.
   nsCOMPtr<nsIGlobalObject> mIncumbentGlobal;
   JS::TenuredHeap<JSObject*> mIncumbentJSGlobal;
   class MOZ_STACK_CLASS CallSetup
   {
     /**
      * A class that performs whatever setup we need to safely make a
      * call while this class is on the stack, After the constructor
      * returns, the call is safe to make if GetContext() returns
      * non-null.
      */
   public:
     // If aExceptionHandling == eRethrowContentExceptions then aCompartment
     // needs to be set to the compartment in which exceptions will be rethrown.
     CallSetup(CallbackObject* aCallback, ErrorResult& aRv,
               ExceptionHandling aExceptionHandling,
               JSCompartment* aCompartment = nullptr,
               bool aIsJSImplementedWebIDL = false);
     ~CallSetup();
     JSContext* GetContext() const
     {
       return mCx;
     }
   private:
     // We better not get copy-constructed
     CallSetup(const CallSetup&) MOZ_DELETE;
     bool ShouldRethrowException(JS::Handle<JS::Value> aException);
     // Members which can go away whenever
     JSContext* mCx;
     // Caller's compartment. This will only have a sensible value if
     // mExceptionHandling == eRethrowContentExceptions.
     JSCompartment* mCompartment;
     // And now members whose construction/destruction order we need to control.
     Maybe<AutoEntryScript> mAutoEntryScript;
     Maybe<AutoIncumbentScript> mAutoIncumbentScript;
     // Constructed the rooter within the scope of mCxPusher above, so that it's
     // always within a request during its lifetime.
     Maybe<JS::Rooted<JSObject*> > mRootedCallable;
     // Can't construct a JSAutoCompartment without a JSContext either.  Also,
     // Put mAc after mAutoEntryScript so that we exit the compartment before
     // we pop the JSContext. Though in practice we'll often manually order
     // those two things.
     Maybe<JSAutoCompartment> mAc;
     // An ErrorResult to possibly re-throw exceptions on and whether
     // we should re-throw them.
     ErrorResult& mErrorResult;
     const ExceptionHandling mExceptionHandling;
     JS::ContextOptions mSavedJSContextOptions;
     const bool mIsMainThread;
   };
 };
 template<class WebIDLCallbackT, class XPCOMCallbackT>
 class CallbackObjectHolder;
 template<class T, class U>
 void ImplCycleCollectionUnlink(CallbackObjectHolder<T, U>& aField);
 class CallbackObjectHolderBase
 {
 protected:
   // Returns null on all failures
   already_AddRefed<nsISupports> ToXPCOMCallback(CallbackObject* aCallback,
                                                 const nsIID& aIID) const;
 };
 template<class WebIDLCallbackT, class XPCOMCallbackT>
 class CallbackObjectHolder : CallbackObjectHolderBase
 {
   /**
    * A class which stores either a WebIDLCallbackT* or an XPCOMCallbackT*.  Both
    * types must inherit from nsISupports.  The pointer that's stored can be
    * null.
    *
    * When storing a WebIDLCallbackT*, mPtrBits is set to the pointer value.
    * When storing an XPCOMCallbackT*, mPtrBits is the pointer value with low bit
    * set.
    */
 public:
   explicit CallbackObjectHolder(WebIDLCallbackT* aCallback)
     : mPtrBits(reinterpret_cast<uintptr_t>(aCallback))
   {
     NS_IF_ADDREF(aCallback);
   }
   explicit CallbackObjectHolder(XPCOMCallbackT* aCallback)
     : mPtrBits(reinterpret_cast<uintptr_t>(aCallback) | XPCOMCallbackFlag)
   {
     NS_IF_ADDREF(aCallback);
   }
   explicit CallbackObjectHolder(const CallbackObjectHolder& aOther)
     : mPtrBits(aOther.mPtrBits)
   {
     NS_IF_ADDREF(GetISupports());
   }
   CallbackObjectHolder()
     : mPtrBits(0)
   {}
   ~CallbackObjectHolder()
   {
     UnlinkSelf();
   }
   void operator=(WebIDLCallbackT* aCallback)
   {
     UnlinkSelf();
     mPtrBits = reinterpret_cast<uintptr_t>(aCallback);
     NS_IF_ADDREF(aCallback);
   }
   void operator=(XPCOMCallbackT* aCallback)
   {
     UnlinkSelf();
     mPtrBits = reinterpret_cast<uintptr_t>(aCallback) | XPCOMCallbackFlag;
     NS_IF_ADDREF(aCallback);
   }
   void operator=(const CallbackObjectHolder& aOther)
   {
     UnlinkSelf();
     mPtrBits = aOther.mPtrBits;
     NS_IF_ADDREF(GetISupports());
   }
   nsISupports* GetISupports() const
   {
     return reinterpret_cast<nsISupports*>(mPtrBits & ~XPCOMCallbackFlag);
   }
   // Boolean conversion operator so people can use this in boolean tests
   operator bool() const
   {
     return GetISupports();
   }
   // Even if HasWebIDLCallback returns true, GetWebIDLCallback() might still
   // return null.
   bool HasWebIDLCallback() const
   {
     return !(mPtrBits & XPCOMCallbackFlag);
   }
   WebIDLCallbackT* GetWebIDLCallback() const
   {
     MOZ_ASSERT(HasWebIDLCallback());
     return reinterpret_cast<WebIDLCallbackT*>(mPtrBits);
   }
   XPCOMCallbackT* GetXPCOMCallback() const
   {
     MOZ_ASSERT(!HasWebIDLCallback());
     return reinterpret_cast<XPCOMCallbackT*>(mPtrBits & ~XPCOMCallbackFlag);
   }
   bool operator==(WebIDLCallbackT* aOtherCallback) const
   {
     if (!aOtherCallback) {
       // If other is null, then we must be null to be equal.
       return !GetISupports();
     }
     if (!HasWebIDLCallback() || !GetWebIDLCallback()) {
       // If other is non-null, then we can't be equal if we have a
       // non-WebIDL callback or a null callback.
       return false;
     }
     return *GetWebIDLCallback() == *aOtherCallback;
   }
   bool operator==(XPCOMCallbackT* aOtherCallback) const
   {
     return (!aOtherCallback && !GetISupports()) ||
       (!HasWebIDLCallback() && GetXPCOMCallback() == aOtherCallback);
   }
   bool operator==(const CallbackObjectHolder& aOtherCallback) const
   {
     if (aOtherCallback.HasWebIDLCallback()) {
       return *this == aOtherCallback.GetWebIDLCallback();
     }
     return *this == aOtherCallback.GetXPCOMCallback();
   }
   // Try to return an XPCOMCallbackT version of this object.
   already_AddRefed<XPCOMCallbackT> ToXPCOMCallback() const
   {
     if (!HasWebIDLCallback()) {
       nsRefPtr<XPCOMCallbackT> callback = GetXPCOMCallback();
       return callback.forget();
     }
     nsCOMPtr<nsISupports> supp =
       CallbackObjectHolderBase::ToXPCOMCallback(GetWebIDLCallback(),
                                                 NS_GET_TEMPLATE_IID(XPCOMCallbackT));
     // ToXPCOMCallback already did the right QI for us.
     return supp.forget().downcast<XPCOMCallbackT>();
   }
   // Try to return a WebIDLCallbackT version of this object.
   already_AddRefed<WebIDLCallbackT> ToWebIDLCallback() const
   {
     if (HasWebIDLCallback()) {
       nsRefPtr<WebIDLCallbackT> callback = GetWebIDLCallback();
       return callback.forget();
     }
     return nullptr;
   }
 private:
   static const uintptr_t XPCOMCallbackFlag = 1u;
   friend void
   ImplCycleCollectionUnlink<WebIDLCallbackT,
                             XPCOMCallbackT>(CallbackObjectHolder& aField);
   void UnlinkSelf()
   {
     // NS_IF_RELEASE because we might have been unlinked before
     nsISupports* ptr = GetISupports();
     NS_IF_RELEASE(ptr);
     mPtrBits = 0;
   }
   uintptr_t mPtrBits;
 };
 NS_DEFINE_STATIC_IID_ACCESSOR(CallbackObject, DOM_CALLBACKOBJECT_IID)
 template<class T, class U>
 inline void
 ImplCycleCollectionTraverse(nsCycleCollectionTraversalCallback& aCallback,
                             CallbackObjectHolder<T, U>& aField,
                             const char* aName,
                             uint32_t aFlags = 0)
 {
   CycleCollectionNoteChild(aCallback, aField.GetISupports(), aName, aFlags);
 }
 template<class T, class U>
 void
 ImplCycleCollectionUnlink(CallbackObjectHolder<T, U>& aField)
 {
   aField.UnlinkSelf();
 }
 } // namespace dom
 } // namespace mozilla
 #endif // mozilla_dom_CallbackObject_h

The Tor Browser / annotate

dom/bindings/CallbackObject.h@97036ab72558 (annotated)

dom/bindings/CallbackObject.h