dom/bindings/CallbackObject.h
author Bob Owen <bobowencode@gmail.com>
Tue, 05 Jan 2016 10:08:57 +0000
changeset 278418 d765b7934fae4c1389ec4d860988a21437aed075
parent 275264 ae0fb501e531985fe7eedb1255d4b92e0cb68326
child 288588 ee3c99e6f6768fd804b58544efd97262cfea4779
permissions -rw-r--r--
Bug 1156742 Part 7: Refactor nsDeviceContext.cpp to use printing surface for size and nsIDeviceContextSpec for DPI and scale. r=roc These changes are to make using an off screen surface behind our DrawTarget in the child easier. It still creates the real printing surface for some of the calculations, removing this will be required for future tightening of the sandbox.

/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
/* vim: set ts=8 sts=2 et sw=2 tw=80: */
/* 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 "nsWrapperCache.h"
#include "nsJSEnvironment.h"
#include "xpcpublic.h"
#include "jsapi.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.  |aCx| is used to capture the current
  // stack, which is later used as an async parent when the callback
  // is invoked.  aCx can be nullptr, in which case no stack is
  // captured.
  explicit CallbackObject(JSContext* aCx, JS::Handle<JSObject*> aCallback,
                          nsIGlobalObject *aIncumbentGlobal)
  {
    if (aCx && JS::RuntimeOptionsRef(aCx).asyncStack()) {
      JS::RootedObject stack(aCx);
      if (!JS::CaptureCurrentStack(aCx, &stack)) {
        JS_ClearPendingException(aCx);
      }
      Init(aCallback, stack, aIncumbentGlobal);
    } else {
      Init(aCallback, nullptr, aIncumbentGlobal);
    }
  }

  JS::Handle<JSObject*> Callback() const
  {
    JS::ExposeObjectToActiveJS(mCallback);
    return CallbackPreserveColor();
  }

  JSObject* GetCreationStack() const
  {
    JSObject* result = mCreationStack;
    if (result) {
      JS::ExposeObjectToActiveJS(result);
    }
    return result;
  }

  void MarkForCC()
  {
    if (mCallback) {
      JS::ExposeObjectToActiveJS(mCallback);
    }
    if (mCreationStack) {
      JS::ExposeObjectToActiveJS(mCreationStack);
    }
  }

  /*
   * 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 or DOMException from the caller's scope,
    // otherwise report it.
    eRethrowContentExceptions,
    // Throw exceptions to the caller code, unless the caller compartment is
    // provided, the exception is not a DOMError or DOMException from the
    // caller compartment, and the caller compartment does not subsume our
    // unwrapped callback.
    eRethrowExceptions
  };

  size_t SizeOfIncludingThis(mozilla::MallocSizeOf aMallocSizeOf) const
  {
    return aMallocSizeOf(this);
  }

protected:
  virtual ~CallbackObject()
  {
    DropJSObjects();
  }

  explicit CallbackObject(CallbackObject* aCallbackObject)
  {
    Init(aCallbackObject->mCallback, aCallbackObject->mCreationStack,
         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, JSObject* aCreationStack,
                   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;
    mCreationStack = aCreationStack;
    if (aIncumbentGlobal) {
      mIncumbentGlobal = aIncumbentGlobal;
      mIncumbentJSGlobal = aIncumbentGlobal->GetGlobalJSObject();
    }
    mozilla::HoldJSObjects(this);
  }

  CallbackObject(const CallbackObject&) = delete;
  CallbackObject& operator =(const CallbackObject&) = delete;

protected:
  void DropJSObjects()
  {
    MOZ_ASSERT_IF(mIncumbentJSGlobal, mCallback);
    if (mCallback) {
      mCallback = nullptr;
      mCreationStack = nullptr;
      mIncumbentJSGlobal = nullptr;
      mozilla::DropJSObjects(this);
    }
  }

  JS::Heap<JSObject*> mCallback;
  JS::Heap<JSObject*> mCreationStack;
  // 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.
    //
    // If aExceptionHandling == eRethrowExceptions then aCompartment may be set
    // to the compartment in which exceptions will be rethrown.  In that case
    // they will only be rethrown if that compartment's principal subsumes the
    // principal of our (unwrapped) callback.
    CallSetup(CallbackObject* aCallback, ErrorResult& aRv,
              const char* aExecutionReason,
              ExceptionHandling aExceptionHandling,
              JSCompartment* aCompartment = nullptr,
              bool aIsJSImplementedWebIDL = false);
    ~CallSetup();

    JSContext* GetContext() const
    {
      return mCx;
    }

  private:
    // We better not get copy-constructed
    CallSetup(const CallSetup&) = 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 or eRethrowExceptions.
    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;

    // Members which are used to set the async stack.
    Maybe<JS::Rooted<JSObject*>> mAsyncStack;
    Maybe<JS::Rooted<JSString*>> mAsyncCause;
    Maybe<JS::AutoSetAsyncStackForNewCalls> mAsyncStackSetter;

    // 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;
    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
  explicit 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()) {
      RefPtr<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()) {
      RefPtr<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