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/* ***** BEGIN LICENSE BLOCK *****
 * Version: MPL 1.1/GPL 2.0/LGPL 2.1
 *
 * The contents of this file are subject to the Mozilla Public License
 * Version 1.1 (the "License"); you may not use this file except in
 * compliance with the License. You may obtain a copy of the License at
 * http://www.mozilla.org/MPL/
 *
 * Software distributed under the License is distributed on an "AS IS" basis,
 * WITHOUT WARRANTY OF ANY KIND, either express or implied. See the License
 * for the specific language governing rights and limitations under the
 * License.
 *
 * The Original Code is mozilla.org code.
 *
 * The Initial Developer of the Original Code is 
 * Boris Zbarsky <bzbarsky@mit.edu>.
 * Portions created by the Initial Developer are Copyright (C) 2003
 * the Initial Developer. All Rights Reserved.
 *
 * Contributor(s):
 *
 *
 * Alternatively, the contents of this file may be used under the terms of
 * either the GNU General Public License Version 2 or later (the "GPL"), or
 * the GNU Lesser General Public License Version 2.1 or later (the "LGPL"),
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 * ***** END LICENSE BLOCK ***** */

#include "imgIDecoderObserver.idl"

interface imgIRequest;
interface nsIChannel;
interface nsIStreamListener;

/**
 * This interface represents a content node that loads images.  The interface
 * exists to allow getting information on the images that the content node
 * loads and to allow registration of observers for the image loads.
 *
 * Implementors of this interface should handle all the mechanics of actually
 * loading an image -- getting the URI, checking with content policies and
 * the security manager to see whether loading the URI is allowed, performing
 * the load, firing any DOM events as needed.
 *
 * An implementation of this interface may support the concepts of a
 * "current" image and a "pending" image.  If it does, a request to change
 * the currently loaded image will start a "pending" request which will
 * become current only when the image is loaded.  It is the responsibility of
 * observers to check which request they are getting notifications for.
 *
 * Observers added in mid-load will not get any notifications they
 * missed.  We should NOT freeze this interface without considering
 * this issue.  (It could be that the image status on imgIRequest is
 * sufficient, when combined with the isImageBlocked() information.)
 *
 * XXXbz Do not freeze without removing imageURIChanged!
 */

[scriptable, uuid(f3138741-353d-4b2b-beb8-01c308428895)]
interface nsIImageLoadingContent : imgIDecoderObserver
{
  /**
   * Request types.  Image loading content nodes attempt to do atomic
   * image changes when the image url is changed.  This means that
   * when the url changes the new image load will start, but the old
   * image will remain the "current" request until the new image is
   * fully loaded.  At that point, the old "current" request will be
   * discarded and the "pending" request will become "current".
   */
  const long UNKNOWN_REQUEST = -1;
  const long CURRENT_REQUEST = 0;
  const long PENDING_REQUEST = 1;

  /**
   * loadingEnabled is used to enable and disable loading in
   * situations where loading images is unwanted.  Note that enabling
   * loading will *not* automatically trigger an image load.
   */
  attribute boolean loadingEnabled;

  /**
   * Returns true if the image load was blocked (by content policies,
   * security manager, etc).  Returns false otherwise.  This always
   * refers to the CURRENT_REQUEST load.
   */
  readonly attribute boolean imageBlocked;

  /**
   * Used to register an image decoder observer.  Typically, this will
   * be a proxy for a frame that wants to paint the image.
   * Notifications from ongoing image loads will be passed to all
   * registered observers.  Notifications for all request types,
   * current and pending, will be passed through.
   *
   * @param aObserver the observer to register
   *
   * @throws NS_ERROR_OUT_OF_MEMORY
   */
  void addObserver(in imgIDecoderObserver aObserver);

  /**
   * Used to unregister an image decoder observer.
   *
   * @param aObserver the observer to unregister
   */
  void removeObserver(in imgIDecoderObserver aObserver);
  
  /**
   * Accessor to get the image requests
   *
   * @param aRequestType a value saying which request is wanted
   *
   * @return the imgIRequest object (may be null, even when no error
   * is thrown)
   *
   * @throws NS_ERROR_UNEXPECTED if the request type requested is not
   * known
   */
  imgIRequest getRequest(in long aRequestType);

  /**
   * Used to find out what type of request one is dealing with (eg
   * which request got passed through to the imgIDecoderObserver
   * interface of an observer)
   *
   * @param aRequest the request whose type we want to know
   *
   * @return an enum value saying what type this request is
   *
   * @throws NS_ERROR_UNEXPECTED if aRequest is not known
   */
  long getRequestType(in imgIRequest aRequest);

  /**
   * loadImageWithChannel allows data from an existing channel to be
   * used as the image data for this content node.
   *
   * @param aChannel the channel that will deliver the data
   *
   * @return a stream listener to pump the image data into
   *
   * @see imgILoader::loadImageWithChannel
   *
   * @throws NS_ERROR_NULL_POINTER if aChannel is null
   */
  nsIStreamListener loadImageWithChannel(in nsIChannel aChannel);

  /**
   * ImageURIChanged is called when the appropriate attributes (eg
   * 'src' for <img> tags) change.  The string passed in is the new
   * uri string.
   */
  // XXXbz The only reason this is not a protected method is that
  // XXXbz <object> and <embed> do everything from frames, not content.
  // XXXbz Once those are moved to content, this method should become
  // XXXbz a protected method on nsImageLoadingContent!
  [noscript] void imageURIChanged(in AString aNewURI);
};
