tor-browser

IDTracker.h (7713B)

---

/* -*- 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_dom_IDTracker_h_
#define mozilla_dom_IDTracker_h_

#include "nsIObserver.h"
#include "nsThreadUtils.h"

class nsAtom;
class nsIContent;
class nsINode;
class nsIURI;
class nsIReferrerInfo;

namespace mozilla::dom {

class Document;
class DocumentOrShadowRoot;
class Element;

/**
* Class to track what element is referenced by a given ID.
*
* To use it, call one of the Reset methods to set it up to watch a given ID.
* Call get() anytime to determine the referenced element (which may be null if
* the element isn't found). When the element changes, ElementChanged
* will be called, so subclass this class if you want to receive that
* notification. ElementChanged runs at safe-for-script time, i.e. outside
* of the content update. Call Unlink() if you want to stop watching
* for changes (get() will then return null).
*
* By default this is a single-shot tracker --- i.e., when ElementChanged
* fires, we will automatically stop tracking. get() will continue to return
* the changed-to element.
* Override IsPersistent to return true if you want to keep tracking after
* the first change.
*/
class IDTracker {
public:
 using Element = mozilla::dom::Element;

 IDTracker();

 ~IDTracker();

 /**
  * Find which element, if any, is referenced.
  */
 Element* get() const { return mElement; }

 /**
  * Set up a reference to another element, identified by the fragment
  * identifier in aURI. If aURI identifies an element in a document that is
  * not aFrom's document, then an ExternalResourceLoad object will be created
  * to load and store that document in the background as a resource document
  * (until we, and any other observers, no longer observe it).
  *
  * This can be called multiple times with different URIs to change which
  * element is being tracked, but these changes do not trigger ElementChanged.
  *
  * @param aFrom The source element that has made the reference to aURI.
  * @param aURI A URI containing a fragment identifier that identifies the
  *   target element.
  * @param aReferrerInfo The referrerInfo for the source element. Needed if
  *   the referenced element is in an external resource document.
  * @param aReferenceImage Whether the reference comes from a -moz-element
  *   property (that is, we're creating a reference an "image element", which
  *   is subject to the document's mozSetImageElement overriding mechanism).
  */
 void ResetToURIWithFragmentID(Element& aFrom, nsIURI* aURI,
                               nsIReferrerInfo* aReferrerInfo,
                               bool aReferenceImage = false);

 /**
  * A variation on ResetToURIWithFragmentID() to set up a reference that
  * consists only of a fragment identifier, referencing an element in the same
  * document as aFrom.
  *
  * @param aFrom The source element that is making the reference.
  * @param aLocalRef The fragment identifier that identifies the target
  *   element. Must begin with "#".
  * @param aBaseURI The URI this url was specified from. Only used to determine
  *   whether we need to reference the source resource document.
  * @param aReferrerInfo The referrerInfo for the source element. Needed if
  *   the referenced element is in an external resource document.
  * @param aReferenceImage See above.
  */
 void ResetToLocalFragmentID(Element& aFrom, const nsAString& aLocalRef,
                             nsIURI* aBaseURI = nullptr,
                             nsIReferrerInfo* aReferrerInfo = nullptr,
                             bool aReferenceImage = false);

 /**
  * A variation on ResetToURIWithFragmentID() to set up a reference that
  * consists of a pre-parsed ID, referencing an element in the same document
  * as aFrom.
  *
  * @param aFrom The source element that is making the reference.
  * @param aID The ID of the target element.
  * @param aReferenceImage See above.
  */
 void ResetToID(Element& aFrom, nsAtom* aID, bool aReferenceImage = false);

 /**
  * Clears the reference. ElementChanged is not triggered. get() will return
  * null.
  */
 void Unlink();

 void Traverse(nsCycleCollectionTraversalCallback* aCB);

protected:
 /** Requests and maybe watches an external resource doc. */
 void ResetToExternalResource(nsIURI* aURI, nsIReferrerInfo* aReferrerInfo,
                              nsAtom* aRef, Element& aFrom,
                              bool aReferenceImage);

 /**
  * Override this to be notified of element changes. Don't forget
  * to call this superclass method to change mElement. This is called
  * at script-runnable time.
  */
 virtual void ElementChanged(Element* aFrom, Element* aTo);

 /**
  * Override this to convert from a single-shot notification to
  * a persistent notification.
  */
 virtual bool IsPersistent() { return false; }

 /**
  * Set ourselves up with our new document.  Note that aDocument might be
  * null.  Either aWatch must be false or aRef must be empty.
  */
 void HaveNewDocumentOrShadowRoot(DocumentOrShadowRoot*, bool aWatch,
                                  nsAtom* aID);

private:
 static bool Observe(Element* aOldElement, Element* aNewElement, void* aData);

 class Notification : public nsISupports {
  public:
   virtual void SetTo(Element* aTo) = 0;
   virtual void Clear() { mTarget = nullptr; }
   virtual ~Notification() = default;

  protected:
   explicit Notification(IDTracker* aTarget) : mTarget(aTarget) {
     MOZ_ASSERT(aTarget, "Must have a target");
   }
   IDTracker* mTarget;
 };

 class ChangeNotification : public mozilla::Runnable, public Notification {
  public:
   ChangeNotification(IDTracker* aTarget, Element* aFrom, Element* aTo);

   // We need to actually declare all of nsISupports, because
   // Notification inherits from it but doesn't declare it.
   NS_DECL_ISUPPORTS_INHERITED
   NS_IMETHOD Run() override {
     if (mTarget) {
       mTarget->mPendingNotification = nullptr;
       mTarget->ElementChanged(mFrom, mTo);
     }
     return NS_OK;
   }
   void SetTo(Element* aTo) override;
   void Clear() override;

  protected:
   virtual ~ChangeNotification();

   RefPtr<Element> mFrom;
   RefPtr<Element> mTo;
 };
 friend class ChangeNotification;

 class DocumentLoadNotification : public Notification, public nsIObserver {
  public:
   DocumentLoadNotification(IDTracker* aTarget, nsAtom* aRef)
       : Notification(aTarget) {
     if (!mTarget->IsPersistent()) {
       mRef = aRef;
     }
   }

   NS_DECL_ISUPPORTS
   NS_DECL_NSIOBSERVER
  private:
   virtual ~DocumentLoadNotification() = default;

   virtual void SetTo(Element* aTo) override {}

   RefPtr<nsAtom> mRef;
 };
 friend class DocumentLoadNotification;

 DocumentOrShadowRoot* GetWatchDocOrShadowRoot() const;

 RefPtr<nsAtom> mWatchID;
 nsCOMPtr<nsINode>
     mWatchDocumentOrShadowRoot;  // Always a `DocumentOrShadowRoot`.
 RefPtr<Element> mElement;
 RefPtr<Notification> mPendingNotification;
 bool mReferencingImage = false;
};

inline void ImplCycleCollectionUnlink(IDTracker& aField) { aField.Unlink(); }

inline void ImplCycleCollectionTraverse(
   nsCycleCollectionTraversalCallback& aCallback, IDTracker& aField,
   const char* aName, uint32_t aFlags = 0) {
 aField.Traverse(&aCallback);
}

}  // namespace mozilla::dom

#endif /* mozilla_dom_IDTracker_h_ */