gecko/content/base/src/nsScriptLoader.h

/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
/* 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 class that handles loading and evaluation of <script> elements.
 */

#ifndef __nsScriptLoader_h__
#define __nsScriptLoader_h__

#include "nsCOMPtr.h"
#include "nsIScriptElement.h"
#include "nsIURI.h"
#include "nsCOMArray.h"
#include "nsTArray.h"
#include "nsAutoPtr.h"
#include "nsIDocument.h"
#include "nsIStreamLoader.h"

class nsScriptLoadRequest;

//////////////////////////////////////////////////////////////
// Script loader implementation
//////////////////////////////////////////////////////////////

class nsScriptLoader : public nsIStreamLoaderObserver
{
  friend class nsScriptRequestProcessor;
public:
  nsScriptLoader(nsIDocument* aDocument);
  virtual ~nsScriptLoader();

  NS_DECL_ISUPPORTS
  NS_DECL_NSISTREAMLOADEROBSERVER

  /**
   * The loader maintains a weak reference to the document with
   * which it is initialized. This call forces the reference to
   * be dropped.
   */
  void DropDocumentReference()
  {
    mDocument = nsnull;
  }

  /**
   * Add an observer for all scripts loaded through this loader.
   *
   * @param aObserver observer for all script processing.
   */
  nsresult AddObserver(nsIScriptLoaderObserver* aObserver)
  {
    return mObservers.AppendObject(aObserver) ? NS_OK :
      NS_ERROR_OUT_OF_MEMORY;
  }

  /**
   * Remove an observer.
   *
   * @param aObserver observer to be removed
   */
  void RemoveObserver(nsIScriptLoaderObserver* aObserver)
  {
    mObservers.RemoveObject(aObserver);
  }
  
  /**
   * Process a script element. This will include both loading the 
   * source of the element if it is not inline and evaluating
   * the script itself.
   *
   * If the script is an inline script that can be executed immediately
   * (i.e. there are no other scripts pending) then ScriptAvailable
   * and ScriptEvaluated will be called before the function returns.
   *
   * If true is returned the script could not be executed immediately.
   * In this case ScriptAvailable is guaranteed to be called at a later
   * point (as well as possibly ScriptEvaluated).
   *
   * @param aElement The element representing the script to be loaded and
   *        evaluated.
   */
  bool ProcessScriptElement(nsIScriptElement* aElement);

  /**
   * Gets the currently executing script. This is useful if you want to
   * generate a unique key based on the currently executing script.
   */
  nsIScriptElement* GetCurrentScript()
  {
    return mCurrentScript;
  }

  nsIScriptElement* GetCurrentParserInsertedScript()
  {
    return mCurrentParserInsertedScript;
  }

  /**
   * Whether the loader is enabled or not.
   * When disabled, processing of new script elements is disabled. 
   * Any call to ProcessScriptElement() will return false. Note that
   * this DOES NOT disable currently loading or executing scripts.
   */
  bool GetEnabled()
  {
    return mEnabled;
  }
  void SetEnabled(bool aEnabled)
  {
    if (!mEnabled && aEnabled) {
      ProcessPendingRequestsAsync();
    }
    mEnabled = aEnabled;
  }

  /**
   * Add/remove blocker. Blockers will stop scripts from executing, but not
   * from loading.
   */
  void AddExecuteBlocker()
  {
    ++mBlockerCount;
  }
  void RemoveExecuteBlocker()
  {
    if (!--mBlockerCount) {
      ProcessPendingRequestsAsync();
    }
  }

  /**
   * Convert the given buffer to a UTF-16 string.
   * @param aChannel     Channel corresponding to the data. May be null.
   * @param aData        The data to convert
   * @param aLength      Length of the data
   * @param aHintCharset Hint for the character set (e.g., from a charset
   *                     attribute). May be the empty string.
   * @param aDocument    Document which the data is loaded for. Must not be
   *                     null.
   * @param aString      [out] Data as converted to unicode
   */
  static nsresult ConvertToUTF16(nsIChannel* aChannel, const PRUint8* aData,
                                 PRUint32 aLength,
                                 const nsAString& aHintCharset,
                                 nsIDocument* aDocument, nsString& aString);

  /**
   * Processes any pending requests that are ready for processing.
   */
  void ProcessPendingRequests();

  /**
   * Check whether it's OK to load a script from aURI in
   * aDocument.
   */
  static nsresult ShouldLoadScript(nsIDocument* aDocument,
                                   nsISupports* aContext,
                                   nsIURI* aURI,
                                   const nsAString &aType);

  /**
   * Check whether it's OK to execute a script loaded via aChannel in
   * aDocument.
   */
  static bool ShouldExecuteScript(nsIDocument* aDocument,
                                    nsIChannel* aChannel);

  /**
   * Starts deferring deferred scripts and puts them in the mDeferredRequests
   * queue instead.
   */
  void BeginDeferringScripts()
  {
    mDeferEnabled = true;
    if (mDocument) {
      mDocument->BlockOnload();
    }
  }

  /**
   * Notifies the script loader that parsing is done.  If aTerminated is true,
   * this will drop any pending scripts that haven't run yet.  Otherwise, it
   * will stops deferring scripts and immediately processes the
   * mDeferredRequests queue.
   *
   * WARNING: This function will synchronously execute content scripts, so be
   * prepared that the world might change around you.
   */
  void ParsingComplete(bool aTerminated);

  /**
   * Returns the number of pending scripts, deferred or not.
   */
  PRUint32 HasPendingOrCurrentScripts()
  {
    return mCurrentScript || mParserBlockingRequest;
  }

  /**
   * Adds aURI to the preload list and starts loading it.
   *
   * @param aURI The URI of the external script.
   * @param aCharset The charset parameter for the script.
   * @param aType The type parameter for the script.
   * @param aCrossOrigin The crossorigin attribute for the script.
   *                     Void if not present.
   */
  virtual void PreloadURI(nsIURI *aURI, const nsAString &aCharset,
                          const nsAString &aType,
                          const nsAString &aCrossOrigin);

private:
  /**
   * Unblocks the creator parser of the parser-blocking scripts.
   */
  void UnblockParser(nsScriptLoadRequest* aParserBlockingRequest);

  /**
   * Asynchronously resumes the creator parser of the parser-blocking scripts.
   */
  void ContinueParserAsync(nsScriptLoadRequest* aParserBlockingRequest);


  /**
   * Helper function to check the content policy for a given request.
   */
  static nsresult CheckContentPolicy(nsIDocument* aDocument,
                                     nsISupports *aContext,
                                     nsIURI *aURI,
                                     const nsAString &aType);

  /**
   * Start a load for aRequest's URI.
   */
  nsresult StartLoad(nsScriptLoadRequest *aRequest, const nsAString &aType);

  /**
   * Process any pending requests asynchronously (i.e. off an event) if there
   * are any. Note that this is a no-op if there aren't any currently pending
   * requests.
   *
   * This function is virtual to allow cross-library calls to SetEnabled()
   */
  virtual void ProcessPendingRequestsAsync();

  /**
   * If true, the loader is ready to execute scripts, and so are all its
   * ancestors.  If the loader itself is ready but some ancestor is not, this
   * function will add an execute blocker and ask the ancestor to remove it
   * once it becomes ready.
   */
  bool ReadyToExecuteScripts();

  /**
   * Return whether just this loader is ready to execute scripts.
   */
  bool SelfReadyToExecuteScripts()
  {
    return mEnabled && !mBlockerCount;
  }

  bool AddPendingChildLoader(nsScriptLoader* aChild) {
    return mPendingChildLoaders.AppendElement(aChild) != nsnull;
  }
  
  nsresult ProcessRequest(nsScriptLoadRequest* aRequest);
  void FireScriptAvailable(nsresult aResult,
                           nsScriptLoadRequest* aRequest);
  void FireScriptEvaluated(nsresult aResult,
                           nsScriptLoadRequest* aRequest);
  nsresult EvaluateScript(nsScriptLoadRequest* aRequest,
                          const nsAFlatString& aScript);

  nsresult PrepareLoadedRequest(nsScriptLoadRequest* aRequest,
                                nsIStreamLoader* aLoader,
                                nsresult aStatus,
                                PRUint32 aStringLen,
                                const PRUint8* aString);

  nsIDocument* mDocument;                   // [WEAK]
  nsCOMArray<nsIScriptLoaderObserver> mObservers;
  nsTArray<nsRefPtr<nsScriptLoadRequest> > mNonAsyncExternalScriptInsertedRequests;
  nsTArray<nsRefPtr<nsScriptLoadRequest> > mAsyncRequests;
  nsTArray<nsRefPtr<nsScriptLoadRequest> > mDeferRequests;
  nsTArray<nsRefPtr<nsScriptLoadRequest> > mXSLTRequests;
  nsRefPtr<nsScriptLoadRequest> mParserBlockingRequest;

  // In mRequests, the additional information here is stored by the element.
  struct PreloadInfo {
    nsRefPtr<nsScriptLoadRequest> mRequest;
    nsString mCharset;
  };

  struct PreloadRequestComparator {
    bool Equals(const PreloadInfo &aPi, nsScriptLoadRequest * const &aRequest)
        const
    {
      return aRequest == aPi.mRequest;
    }
  };
  struct PreloadURIComparator {
    bool Equals(const PreloadInfo &aPi, nsIURI * const &aURI) const;
  };
  nsTArray<PreloadInfo> mPreloads;

  nsCOMPtr<nsIScriptElement> mCurrentScript;
  nsCOMPtr<nsIScriptElement> mCurrentParserInsertedScript;
  // XXXbz do we want to cycle-collect these or something?  Not sure.
  nsTArray< nsRefPtr<nsScriptLoader> > mPendingChildLoaders;
  PRUint32 mBlockerCount;
  bool mEnabled;
  bool mDeferEnabled;
  bool mDocumentParsingDone;
};

class nsAutoScriptLoaderDisabler
{
public:
  nsAutoScriptLoaderDisabler(nsIDocument* aDoc)
  {
    mLoader = aDoc->ScriptLoader();
    mWasEnabled = mLoader->GetEnabled();
    if (mWasEnabled) {
      mLoader->SetEnabled(false);
    }
  }
  
  ~nsAutoScriptLoaderDisabler()
  {
    if (mWasEnabled) {
      mLoader->SetEnabled(true);
    }
  }
  
  bool mWasEnabled;
  nsRefPtr<nsScriptLoader> mLoader;
};

#endif //__nsScriptLoader_h__