Bug 1493709 - Do not report error of dump load in RemoteSettings.get() r=glasserc

If the collection has no local dump, it should not report any error while trying to load the dump.

Differential Revision: https://phabricator.services.mozilla.com/D7889

--HG--
extra : moz-landing-system : lando

services/settings/remote-settings.js

@@ -227,15 +227,27 @@ async function fetchLatestChanges(url, lastEtag, expectedTimestamp) {
  * Load the the JSON file distributed with the release for this collection.
  * @param {String}  bucket
  * @param {String}  collection
+ * @param {Object}  options
+ * @param {boolean} options.ignoreMissing Do not throw an error if the file is missing.
  */
-async function loadDumpFile(bucket, collection) {
+async function loadDumpFile(bucket, collection, { ignoreMissing = true } = {}) {
   const fileURI = `resource://app/defaults/settings/${bucket}/${collection}.json`;
-  const response = await fetch(fileURI);
+  let response;
+  try {
+    // Will throw NetworkError is folder/file is missing.
+    response = await fetch(fileURI);
     if (!response.ok) {
       throw new Error(`Could not read from '${fileURI}'`);
     }
-  // Will be rejected if JSON is invalid.
+    // Will throw if JSON is invalid.
     return response.json();
+  } catch (e) {
+    // A missing file is reported as "NetworError" (see Bug 1493709)
+    if (!ignoreMissing || !/NetworkError/.test(e.message)) {
+      throw e;
+    }
+  }
+  return { data: [] };
 }
 
 
@@ -616,7 +628,7 @@ async function hasLocalData(client) {
  */
 async function hasLocalDump(bucket, collection) {
   try {
-    await loadDumpFile(bucket, collection);
+    await loadDumpFile(bucket, collection, {ignoreMissing: false});
     return true;
   } catch (e) {
     return false;