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mmv.provider.Image.js
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mmv.provider.Image.js
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/*
* This file is part of the MediaWiki extension MultimediaViewer.
*
* MultimediaViewer is free software: you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation, either version 2 of the License, or
* (at your option) any later version.
*
* MultimediaViewer is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with MultimediaViewer. If not, see <http://www.gnu.org/licenses/>.
*/
const config = require( '../config.json' );
/**
* Loads an image.
*/
class ImageProvider {
/**
* @param {string} imageQueryParameter When defined, is a query parameter to add to every image request
*/
constructor( imageQueryParameter = config.imageQueryParameter ) {
this.imageQueryParameter = imageQueryParameter;
/**
* AJAX call cache.
*
* @property {Object.<string, jQuery.Promise>} cache
* @protected
*/
this.cache = {};
}
/**
* Loads an image and returns it. When the browser supports it, the image is loaded as an AJAX
* request.
*
* @param {string} url
* @return {jQuery.Promise.<HTMLImageElement>} A promise which resolves to the image object.
* When loaded via AJAX, it has progress events, which return an array with the content loaded
* so far and with the progress as a floating-point number between 0 and 100.
*/
get( url ) {
const cacheKey = url;
if ( this.imageQueryParameter ) {
try {
const uri = new URL( url, location );
uri.searchParams.set( this.imageQueryParameter, '' );
url = uri.toString();
} catch ( error ) {
return $.Deferred().reject( error.message );
}
}
if ( !this.cache[ cacheKey ] ) {
this.cache[ cacheKey ] = this.rawGet( url, this.imagePreloadingSupported() );
this.cache[ cacheKey ].fail( ( error ) => {
mw.log( `${ this.constructor.name } provider failed to load: `, error );
} );
}
return this.cache[ cacheKey ];
}
/**
* Internal version of get(): no caching, no performance metrics.
*
* @param {string} url
* @param {boolean} [cors] if true, use CORS for preloading
* @return {jQuery.Promise.<HTMLImageElement>} a promise which resolves to the image object
*/
rawGet( url, cors ) {
const img = new window.Image();
const deferred = $.Deferred();
// This attribute is necessary in Firefox, which needs it for the image request after
// the XHR to hit the cache by being a proper CORS request.
if ( cors ) {
img.crossOrigin = 'anonymous';
}
img.onload = () => deferred.resolve( img );
img.onerror = () => deferred.reject( `could not load image from ${ url }` );
img.src = url;
return deferred;
}
/**
* Checks whether the current browser supports AJAX preloading of images.
* This means that:
* - the browser supports CORS requests (large wiki farms usually host images on a
* separate domain) and
* - either AJAX and normal image loading uses the same cache (when an image is used by a CORS
* request, and then normally by setting img.src, it is only loaded once)
* - or (as is the case with Firefox) they are cached separately, but that can be changed by
* setting the crossOrigin attribute
*
* @return {boolean}
*/
imagePreloadingSupported() {
// This checks if the browser supports CORS requests in XHRs
return window.XMLHttpRequest !== undefined && 'withCredentials' in new XMLHttpRequest();
}
}
module.exports = ImageProvider;

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