1 files changed, 77 insertions, 0 deletions
diff --git a/devtools/client/shared/getjson.js b/devtools/client/shared/getjson.js
new file mode 100644
index 0000000000..831382c310
--- /dev/null
+++ b/devtools/client/shared/getjson.js
@@ -0,0 +1,77 @@
+/* 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 Services = require("Services");
+
+loader.lazyRequireGetter(this, "asyncStorage", "devtools/shared/async-storage");
+
+/**
+ * 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) {
+  return new Promise((resolve, reject) => {
+    const 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")) {
+      const 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 reject("Empty cache for " + prefName);
+          }
+          return resolve(json);
+        })
+        .catch(function(e) {
+          reject(
+            "JSON not available, CDN error: " +
+              networkError +
+              ", storage error: " +
+              e
+          );
+        });
+    }
+
+    xhr.onload = () => {
+      try {
+        const 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);
+        });
+        resolve(json);
+      } catch (e) {
+        readFromStorage(e);
+      }
+    };
+
+    xhr.onerror = e => {
+      readFromStorage(e);
+    };
+
+    xhr.open("get", Services.prefs.getCharPref(prefName));
+    xhr.send();
+  });
+};