dom/events/JSEventHandler.h

/* -*- 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/. */

#ifndef mozilla_JSEventHandler_h_
#define mozilla_JSEventHandler_h_

#include "mozilla/Attributes.h"
#include "mozilla/MemoryReporting.h"
#include "mozilla/dom/EventHandlerBinding.h"
#include "nsCOMPtr.h"
#include "nsCycleCollectionParticipant.h"
#include "nsAtom.h"
#include "nsIDOMEventListener.h"
#include "nsIScriptContext.h"

namespace mozilla {

class TypedEventHandler {
 public:
  enum HandlerType {
    eUnset = 0,
    eNormal = 0x1,
    eOnError = 0x2,
    eOnBeforeUnload = 0x3,
    eTypeBits = 0x3
  };

  TypedEventHandler() : mBits(0) {}

  explicit TypedEventHandler(dom::EventHandlerNonNull* aHandler) : mBits(0) {
    Assign(aHandler, eNormal);
  }

  explicit TypedEventHandler(dom::OnErrorEventHandlerNonNull* aHandler)
      : mBits(0) {
    Assign(aHandler, eOnError);
  }

  explicit TypedEventHandler(dom::OnBeforeUnloadEventHandlerNonNull* aHandler)
      : mBits(0) {
    Assign(aHandler, eOnBeforeUnload);
  }

  TypedEventHandler(const TypedEventHandler& aOther) {
    if (aOther.HasEventHandler()) {
      // Have to make sure we take our own ref
      Assign(aOther.Ptr(), aOther.Type());
    } else {
      mBits = 0;
    }
  }

  ~TypedEventHandler() { ReleaseHandler(); }

  HandlerType Type() const { return HandlerType(mBits & eTypeBits); }

  bool HasEventHandler() const { return !!Ptr(); }

  void SetHandler(const TypedEventHandler& aHandler) {
    if (aHandler.HasEventHandler()) {
      ReleaseHandler();
      Assign(aHandler.Ptr(), aHandler.Type());
    } else {
      ForgetHandler();
    }
  }

  dom::EventHandlerNonNull* NormalEventHandler() const {
    MOZ_ASSERT(Type() == eNormal && Ptr());
    return reinterpret_cast<dom::EventHandlerNonNull*>(Ptr());
  }

  void SetHandler(dom::EventHandlerNonNull* aHandler) {
    ReleaseHandler();
    Assign(aHandler, eNormal);
  }

  dom::OnBeforeUnloadEventHandlerNonNull* OnBeforeUnloadEventHandler() const {
    MOZ_ASSERT(Type() == eOnBeforeUnload);
    return reinterpret_cast<dom::OnBeforeUnloadEventHandlerNonNull*>(Ptr());
  }

  void SetHandler(dom::OnBeforeUnloadEventHandlerNonNull* aHandler) {
    ReleaseHandler();
    Assign(aHandler, eOnBeforeUnload);
  }

  dom::OnErrorEventHandlerNonNull* OnErrorEventHandler() const {
    MOZ_ASSERT(Type() == eOnError);
    return reinterpret_cast<dom::OnErrorEventHandlerNonNull*>(Ptr());
  }

  void SetHandler(dom::OnErrorEventHandlerNonNull* aHandler) {
    ReleaseHandler();
    Assign(aHandler, eOnError);
  }

  dom::CallbackFunction* Ptr() const {
    // Have to cast eTypeBits so we don't have to worry about
    // promotion issues after the bitflip.
    return reinterpret_cast<dom::CallbackFunction*>(mBits &
                                                    ~uintptr_t(eTypeBits));
  }

  void ForgetHandler() {
    ReleaseHandler();
    mBits = 0;
  }

  bool operator==(const TypedEventHandler& aOther) const {
    return Ptr() && aOther.Ptr() &&
           Ptr()->CallbackPreserveColor() ==
               aOther.Ptr()->CallbackPreserveColor();
  }

 private:
  void operator=(const TypedEventHandler&) = delete;

  void ReleaseHandler() {
    nsISupports* ptr = Ptr();
    NS_IF_RELEASE(ptr);
  }

  void Assign(nsISupports* aHandler, HandlerType aType) {
    MOZ_ASSERT(aHandler, "Must have handler");
    NS_ADDREF(aHandler);
    mBits = uintptr_t(aHandler) | uintptr_t(aType);
  }

  uintptr_t mBits;
};

/**
 * Implemented by script event listeners. Used to retrieve the script object
 * corresponding to the event target and the handler itself.
 *
 * Note, mTarget is a raw pointer and the owner of the JSEventHandler object
 * is expected to call Disconnect()!
 */

#define NS_JSEVENTHANDLER_IID                        \
  {                                                  \
    0x4f486881, 0x1956, 0x4079, {                    \
      0x8c, 0xa0, 0xf3, 0xbd, 0x60, 0x5c, 0xc2, 0x79 \
    }                                                \
  }

class JSEventHandler : public nsIDOMEventListener {
 public:
  NS_DECLARE_STATIC_IID_ACCESSOR(NS_JSEVENTHANDLER_IID)

  JSEventHandler(nsISupports* aTarget, nsAtom* aType,
                 const TypedEventHandler& aTypedHandler);

  NS_DECL_CYCLE_COLLECTING_ISUPPORTS

  // nsIDOMEventListener interface
  NS_DECL_NSIDOMEVENTLISTENER

  nsISupports* GetEventTarget() const { return mTarget; }

  void Disconnect() { mTarget = nullptr; }

  const TypedEventHandler& GetTypedEventHandler() const {
    return mTypedHandler;
  }

  void ForgetHandler() { mTypedHandler.ForgetHandler(); }

  nsAtom* EventName() const { return mEventName; }

  // Set a handler for this event listener.  The handler must already
  // be bound to the right target.
  void SetHandler(const TypedEventHandler& aTypedHandler) {
    mTypedHandler.SetHandler(aTypedHandler);
  }
  void SetHandler(dom::EventHandlerNonNull* aHandler) {
    mTypedHandler.SetHandler(aHandler);
  }
  void SetHandler(dom::OnBeforeUnloadEventHandlerNonNull* aHandler) {
    mTypedHandler.SetHandler(aHandler);
  }
  void SetHandler(dom::OnErrorEventHandlerNonNull* aHandler) {
    mTypedHandler.SetHandler(aHandler);
  }

  size_t SizeOfExcludingThis(MallocSizeOf aMallocSizeOf) const {
    return 0;

    // Measurement of the following members may be added later if DMD finds it
    // is worthwhile:
    // - mTarget
    //
    // The following members are not measured:
    // - mTypedHandler: may be shared with others
    // - mEventName: shared with others
  }

  size_t SizeOfIncludingThis(MallocSizeOf aMallocSizeOf) {
    return aMallocSizeOf(this) + SizeOfExcludingThis(aMallocSizeOf);
  }

  NS_DECL_CYCLE_COLLECTION_SKIPPABLE_CLASS(JSEventHandler)

  bool IsBlackForCC();

 protected:
  virtual ~JSEventHandler();

  nsISupports* mTarget;
  RefPtr<nsAtom> mEventName;
  TypedEventHandler mTypedHandler;
};

NS_DEFINE_STATIC_IID_ACCESSOR(JSEventHandler, NS_JSEVENTHANDLER_IID)

}  // namespace mozilla

/**
 * Factory function.  aHandler must already be bound to aTarget.
 * aContext is allowed to be null if aHandler is already set up.
 */
nsresult NS_NewJSEventHandler(nsISupports* aTarget, nsAtom* aType,
                              const mozilla::TypedEventHandler& aTypedHandler,
                              mozilla::JSEventHandler** aReturn);

#endif  // mozilla_JSEventHandler_h_