nsScriptLoader.h

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 * for the specific language governing rights and limitations under the
 * License.
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 * The Original Code is Mozilla.
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 * The Initial Developer of the Original Code is
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 * Contributor(s):
 *   Vidur Apparao <vidur@netscape.com> (original author)
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/*
 * 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
{
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 NS_ERROR_HTMLPARSER_BLOCK 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.
   */
  nsresult 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;
  }

  /**
   * Whether the loader is enabled or not.
   * When disabled, processing of new script elements is disabled. 
   * Any call to ProcessScriptElement() will fail with a return code of
   * NS_ERROR_NOT_AVAILABLE. Note that this DOES NOT disable
   * currently loading or executing scripts.
   */
  PRBool GetEnabled()
  {
    return mEnabled;
  }
  void SetEnabled(PRBool 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 nsString& aHintCharset,
                                 nsIDocument* aDocument, nsString& aString);

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

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

protected:
  /**
   * Process any pending requests asyncronously (i.e. off an event) if there
   * are any. Note that this is a no-op if there aren't any currently pending
   * requests.
   */
  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.
   */
  PRBool ReadyToExecuteScripts();

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

  PRBool 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;
  nsCOMArray<nsScriptLoadRequest> mPendingRequests;
  nsCOMPtr<nsIScriptElement> mCurrentScript;
  // XXXbz do we want to cycle-collect these or something?  Not sure.
  nsTArray< nsRefPtr<nsScriptLoader> > mPendingChildLoaders;
  PRUint32 mBlockerCount;
  PRPackedBool mEnabled;
};

#endif //__nsScriptLoader_h__