Proyectos de Subversion Moodle

// This file is part of Moodle - http://moodle.org/

//

// Moodle 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 3 of the License, or

// (at your option) any later version.

//

// Moodle 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 Moodle.  If not, see <http://www.gnu.org/licenses/>.

/**

 * Wrap an instance of the browser's local or session storage to handle

 * cache expiry, key namespacing and other helpful things.

 *

 * @module     core/storagewrapper

 * @copyright  2017 Ryan Wyllie <ryan@moodle.com>

 * @license    http://www.gnu.org/copyleft/gpl.html GNU GPL v3 or later

 */

define(['core/config'], function(config) {

    /**

     * Constructor.

     *

     * @param {object} storage window.localStorage or window.sessionStorage

     */

    var Wrapper = function(storage) {

        this.storage = storage;

        this.supported = this.detectSupport();

        this.hashSource = config.wwwroot + '/' + config.jsrev;

        this.hash = this.hashString(this.hashSource);

        this.prefix = this.hash + '/';

        this.jsrevPrefix = this.hashString(config.wwwroot) + '/jsrev';

        this.validateCache();

    };

    /**

     * Check if the browser supports the type of storage.

     *

     * @method detectSupport

     * @return {boolean} True if the browser supports storage.

     */

    Wrapper.prototype.detectSupport = function() {

        if (config.jsrev == -1) {

            // Disable cache if debugging.

            return false;

        }

        if (typeof (this.storage) === "undefined") {

            return false;

        }

        var testKey = 'test';

        try {

            if (this.storage === null) {

                return false;

            }

            // MDL-51461 - Some browsers misreport availability of the storage

            // so check it is actually usable.

            this.storage.setItem(testKey, '1');

            this.storage.removeItem(testKey);

            return true;

        } catch (ex) {

            return false;

        }

    };

    /**

     * Add a unique prefix to all keys so multiple moodle sites do not share caches.

     *

     * @method prefixKey

     * @param {string} key The cache key to prefix.

     * @return {string} The new key

     */

    Wrapper.prototype.prefixKey = function(key) {

        return this.prefix + key;

    };

    /**

     * Check the current jsrev version and clear the cache if it has been bumped.

     *

     * @method validateCache

     */

    Wrapper.prototype.validateCache = function() {

        if (!this.supported) {

            return;

        }

        var cacheVersion = this.storage.getItem(this.jsrevPrefix);

        if (cacheVersion === null) {

            this.storage.setItem(this.jsrevPrefix, config.jsrev);

            return;

        }

        var moodleVersion = config.jsrev;

        if (moodleVersion != cacheVersion) {

            this.storage.clear();

            this.storage.setItem(this.jsrevPrefix, config.jsrev);

        }

    };

    /**

     * Hash a string, used to make shorter key prefixes.

     *

     * @method hashString

     * @param {String} source The string to hash

     * @return {Number}

     */

    Wrapper.prototype.hashString = function(source) {

        // From http://stackoverflow.com/questions/7616461/generate-a-hash-from-string-in-javascript-jquery.

        /* jshint bitwise: false */

        /* eslint no-bitwise: "off" */

        var hash = 0;

        var i, chr, len;

        if (source.length === 0) {

            return hash;

        }

        for (i = 0, len = source.length; i < len; i++) {

            chr = source.charCodeAt(i);

            hash = ((hash << 5) - hash) + chr;

            hash |= 0; // Convert to 32bit integer

        }

        return hash;

    };

    /**

     * Get a value from local storage. Remember - all values must be strings.

     *

     * @method get

     * @param {string} key The cache key to check.

     * @return {boolean|string} False if the value is not in the cache, or some other error - a string otherwise.

     */

    Wrapper.prototype.get = function(key) {

        if (!this.supported) {

            return false;

        }

        key = this.prefixKey(key);

        return this.storage.getItem(key);

    };

    /**

     * Set a value to local storage. Remember - all values must be strings.

     *

     * @method set

     * @param {string} key The cache key to set.

     * @param {string} value The value to set.

     * @return {boolean} False if the value can't be saved in the cache, or some other error - true otherwise.

     */

    Wrapper.prototype.set = function(key, value) {

        if (!this.supported) {

            return false;

        }

        key = this.prefixKey(key);

        // This can throw exceptions when the storage limit is reached.

        try {

            this.storage.setItem(key, value);

        } catch (e) {

            return false;

        }

        return true;

    };

    /**

     * Clean local storage.

     *

     * @method clean

     */

    Wrapper.prototype.clean = function() {

        this.storage.clear();

    };

    return Wrapper;

});