1 files changed, 76 insertions, 0 deletions
diff --git a/devtools/client/shared/getjson.js b/devtools/client/shared/getjson.js
new file mode 100644
index 000000000..3c4d48e07
--- /dev/null
+++ b/devtools/client/shared/getjson.js
@@ -0,0 +1,76 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+"use strict";
+
+const {CC} = require("chrome");
+const defer = require("devtools/shared/defer");
+const promise = require("promise");
+const Services = require("Services");
+
+loader.lazyRequireGetter(this, "asyncStorage", "devtools/shared/async-storage");
+
+const XMLHttpRequest = CC("@mozilla.org/xmlextras/xmlhttprequest;1");
+
+/**
+ * Downloads and caches a JSON file from an URL given by a pref.
+ *
+ * @param {String} prefName
+ *        The preference for the target URL
+ *
+ * @return {Promise}
+ *         - Resolved with the JSON object in case of successful request
+ *           or cache hit
+ *         - Rejected with an error message in case of failure
+ */
+exports.getJSON = function (prefName) {
+  let deferred = defer();
+  let xhr = new XMLHttpRequest();
+
+  // We used to store cached data in preferences, but now we use asyncStorage
+  // Migration step: if it still exists, move this now useless preference in its
+  // new location and clear it
+  if (Services.prefs.prefHasUserValue(prefName + "_cache")) {
+    let json = Services.prefs.getCharPref(prefName + "_cache");
+    asyncStorage.setItem(prefName + "_cache", json).catch(function (e) {
+      // Could not move the cache, let's log the error but continue
+      console.error(e);
+    });
+    Services.prefs.clearUserPref(prefName + "_cache");
+  }
+
+  function readFromStorage(networkError) {
+    asyncStorage.getItem(prefName + "_cache").then(function (json) {
+      if (!json) {
+        return promise.reject("Empty cache for " + prefName);
+      }
+      return deferred.resolve(json);
+    }).catch(function (e) {
+      deferred.reject("JSON not available, CDN error: " + networkError +
+                      ", storage error: " + e);
+    });
+  }
+
+  xhr.onload = () => {
+    try {
+      let json = JSON.parse(xhr.responseText);
+      asyncStorage.setItem(prefName + "_cache", json).catch(function (e) {
+        // Could not update cache, let's log the error but continue
+        console.error(e);
+      });
+      deferred.resolve(json);
+    } catch (e) {
+      readFromStorage(e);
+    }
+  };
+
+  xhr.onerror = (e) => {
+    readFromStorage(e);
+  };
+
+  xhr.open("get", Services.prefs.getCharPref(prefName));
+  xhr.send();
+
+  return deferred.promise;
+};