Bug 1727487 - Notify observers of synchronization errors (r=mixedpuppy)

Differential Revision: https://phabricator.services.mozilla.com/D123597

services/settings/docs/index.rst

@@ -324,6 +324,8 @@ The polling for changes process sends two notifications that observers can regis
 
 * ``remote-settings:changes-poll-start``: Polling for changes is starting. triggered either by the scheduled timer or a push broadcast.
 * ``remote-settings:changes-poll-end``: Polling for changes has ended
+* ``remote-settings:sync-error``: A synchronization error occured. Notification subject provides information about the error and affected
+  collection in the ``wrappedJSObject`` attribute.
 
 .. code-block:: javascript
 

services/settings/remote-settings.js

@@ -342,6 +342,11 @@ function remoteSettingsFunction() {
         UptakeTelemetry.STATUS.SYNC_ERROR,
         syncTelemetryArgs
       );
+      // Notify potential observers of the error.
+      Services.obs.notifyObservers(
+        { wrappedJSObject: { error: firstError } },
+        "remote-settings:sync-error"
+      );
       // Rethrow the first observed error
       throw firstError;
     }

services/settings/test/unit/test_remote_settings_poll.js

@@ -723,34 +723,34 @@ add_task(async function test_client_error() {
     TELEMETRY_HISTOGRAM_SYNC_KEY
   );
 
-  server.registerPathHandler(
-    CHANGES_PATH,
-    serveChangesEntries(10000, [
-      {
+  const collectionDetails = {
     id: "b6ba7fab-a40a-4d03-a4af-6b627f3c5b36",
     last_modified: 42,
     host: "localhost",
     bucket: "main",
     collection: "some-entry",
-      },
-    ])
+  };
+  server.registerPathHandler(
+    CHANGES_PATH,
+    serveChangesEntries(10000, [collectionDetails])
   );
   const c = RemoteSettings("some-entry");
   c.maybeSync = () => {
-    throw new Error("boom");
+    throw new RemoteSettingsClient.CorruptedDataError("main/some-entry");
   };
 
-  let notificationObserved = false;
+  let notificationsObserved = [];
   const observer = {
     observe(aSubject, aTopic, aData) {
-      Services.obs.removeObserver(this, "remote-settings:changes-poll-end");
-      notificationObserved = true;
+      Services.obs.removeObserver(this, aTopic);
+      notificationsObserved.push([aTopic, aSubject.wrappedJSObject]);
     },
   };
   Services.obs.addObserver(observer, "remote-settings:changes-poll-end");
+  Services.obs.addObserver(observer, "remote-settings:sync-error");
   Services.prefs.setIntPref(PREF_LAST_ETAG, 42);
 
-  // pollChanges() fails with adequate error and no notification.
+  // pollChanges() fails with adequate error and a sync-error notification.
   let error;
   try {
     await RemoteSettings.pollChanges();
@@ -758,11 +758,25 @@ add_task(async function test_client_error() {
     error = e;
   }
 
-  Assert.ok(
-    !notificationObserved,
-    "a notification should not have been observed"
+  Assert.equal(
+    notificationsObserved.length,
+    1,
+    "only the error notification should not have been observed"
   );
-  Assert.ok(/boom/.test(error.message), "original client error is thrown");
+  console.log(notificationsObserved);
+  let [topicObserved, subjectObserved] = notificationsObserved[0];
+  Assert.equal(topicObserved, "remote-settings:sync-error");
+  Assert.ok(
+    subjectObserved.error instanceof RemoteSettingsClient.CorruptedDataError,
+    `original error is provided (got ${subjectObserved.error})`
+  );
+  Assert.deepEqual(
+    subjectObserved.error.details,
+    collectionDetails,
+    "information about collection is provided"
+  );
+
+  Assert.ok(/Corrupted/.test(error.message), "original client error is thrown");
   // When an error occurs, last etag was not overwritten.
   Assert.equal(Services.prefs.getIntPref(PREF_LAST_ETAG), 42);
   // ensure that we've accumulated the correct telemetry