77 lines
2.4 KiB
JavaScript
77 lines
2.4 KiB
JavaScript
/* This Source Code Form is subject to the terms of the Mozilla Public
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* License, v. 2.0. If a copy of the MPL was not distributed with this
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* file, You can obtain one at http://mozilla.org/MPL/2.0/. */
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"use strict";
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const {CC} = require("chrome");
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const defer = require("devtools/shared/defer");
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const promise = require("promise");
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const Services = require("Services");
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loader.lazyRequireGetter(this, "asyncStorage", "devtools/shared/async-storage");
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const XMLHttpRequest = CC("@mozilla.org/xmlextras/xmlhttprequest;1");
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/**
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* Downloads and caches a JSON file from an URL given by a pref.
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*
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* @param {String} prefName
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* The preference for the target URL
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*
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* @return {Promise}
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* - Resolved with the JSON object in case of successful request
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* or cache hit
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* - Rejected with an error message in case of failure
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*/
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exports.getJSON = function (prefName) {
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let deferred = defer();
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let xhr = new XMLHttpRequest();
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// We used to store cached data in preferences, but now we use asyncStorage
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// Migration step: if it still exists, move this now useless preference in its
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// new location and clear it
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if (Services.prefs.prefHasUserValue(prefName + "_cache")) {
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let json = Services.prefs.getCharPref(prefName + "_cache");
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asyncStorage.setItem(prefName + "_cache", json).catch(function (e) {
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// Could not move the cache, let's log the error but continue
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console.error(e);
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});
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Services.prefs.clearUserPref(prefName + "_cache");
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}
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function readFromStorage(networkError) {
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asyncStorage.getItem(prefName + "_cache").then(function (json) {
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if (!json) {
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return promise.reject("Empty cache for " + prefName);
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}
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return deferred.resolve(json);
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}).catch(function (e) {
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deferred.reject("JSON not available, CDN error: " + networkError +
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", storage error: " + e);
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});
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}
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xhr.onload = () => {
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try {
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let json = JSON.parse(xhr.responseText);
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asyncStorage.setItem(prefName + "_cache", json).catch(function (e) {
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// Could not update cache, let's log the error but continue
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console.error(e);
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});
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deferred.resolve(json);
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} catch (e) {
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readFromStorage(e);
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}
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};
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xhr.onerror = (e) => {
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readFromStorage(e);
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};
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xhr.open("get", Services.prefs.getCharPref(prefName));
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xhr.send();
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return deferred.promise;
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};
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