store: Report non-transient polling errors.

Signed-off-by: Zixuan James Li <zixuan@zulip.com>

Author: PIG208

assets/l10n/app_en.arb

@@ -160,6 +160,13 @@
       "message": {"type": "String", "example": "Invalid format"}
     }
   },
+  "errorLoadingServerData": "Error loading server data. Will retry:\n\n{error}",
+  "@errorLoadingServerData": {
+    "description": "Dialog message for a generic unknown error.",
+    "placeholders": {
+      "error": {"type": "String", "example": "Invalid format"}
+    }
+  },
   "errorSharingFailed": "Sharing failed",
   "@errorSharingFailed": {
     "description": "Error message when sharing a message failed."

lib/model/store.dart

@@ -20,6 +20,7 @@ import '../log.dart';
 import '../notifications/receive.dart';
 import 'autocomplete.dart';
 import 'database.dart';
+import 'localizations.dart';
 import 'message.dart';
 import 'message_list.dart';
 import 'recent_dm_conversations.dart';
@@ -782,6 +783,7 @@ class UpdateMachine {
           queueId: queueId, lastEventId: lastEventId);
       } catch (e) {
         store.isLoading = true;
+        final localizations = GlobalLocalizations.zulipLocalizations;
         switch (e) {
           case ZulipApiException(code: 'BAD_EVENT_QUEUE_ID'):
             assert(debugLog('Lost event queue for $store.  Replacing…'));
@@ -802,7 +804,9 @@ class UpdateMachine {
           default:
             assert(debugLog('Error polling event queue for $store: $e\n'
                 'Backing off and retrying even though may be hopeless…'));
-            // TODO tell user on non-transient error in polling
+            // TODO(#186): Handle unrecoverable failures
+            reportErrorToUserInDialog(
+              localizations.errorLoadingServerData(e.toString()));
             await (backoffMachine ??= BackoffMachine()).wait();
             assert(debugLog('… Backoff wait complete, retrying poll.'));
             continue;

test/model/store_test.dart

@@ -8,6 +8,7 @@ import 'package:zulip/api/model/events.dart';
 import 'package:zulip/api/model/model.dart';
 import 'package:zulip/api/route/events.dart';
 import 'package:zulip/api/route/messages.dart';
+import 'package:zulip/log.dart';
 import 'package:zulip/model/store.dart';
 import 'package:zulip/notifications/receive.dart';
 
@@ -427,53 +428,61 @@ void main() {
       check(store.userSettings!.twentyFourHourTime).isTrue();
     }));
 
-    void checkRetry(String description, void Function() prepareError) {
-      test(description, () {
-        awaitFakeAsync((async) async {
-          await prepareStore(lastEventId: 1);
-          updateMachine.debugPauseLoop();
-          updateMachine.poll();
-          check(async.pendingTimers).length.equals(0);
-
-          // Make the request, inducing an error in it.
-          prepareError();
-          updateMachine.debugAdvanceLoop();
-          async.elapse(Duration.zero);
-          checkLastRequest(lastEventId: 1);
-          check(store).isLoading.isTrue();
-
-          // Polling doesn't resume immediately; there's a timer.
-          check(async.pendingTimers).length.equals(1);
-          updateMachine.debugAdvanceLoop();
-          async.flushMicrotasks();
-          check(connection.lastRequest).isNull();
-          check(async.pendingTimers).length.equals(1);
-
-          // Polling continues after a timer.
-          connection.prepare(json: GetEventsResult(events: [
-            HeartbeatEvent(id: 2),
-          ], queueId: null).toJson());
-          async.flushTimers();
-          checkLastRequest(lastEventId: 1);
-          check(updateMachine.lastEventId).equals(2);
-          check(store).isLoading.isFalse();
-        });
+    void checkRetry(void Function() prepareError, {
+      String? errorMessage,
+    }) {
+      awaitFakeAsync((async) async {
+        await prepareStore(lastEventId: 1);
+        updateMachine.debugPauseLoop();
+        updateMachine.poll();
+        check(async.pendingTimers).length.equals(0);
+
+        // Make the request, inducing an error in it.
+        prepareError();
+        updateMachine.debugAdvanceLoop();
+        check(debugLastReportedError).isNull();
+        async.elapse(Duration.zero);
+        if (errorMessage == null) {
+          check(debugTakeLastReportedError()).isNull();
+        } else {
+          check(debugTakeLastReportedError()).isNotNull().contains(errorMessage);
+        }
+        checkLastRequest(lastEventId: 1);
+        check(store).isLoading.isTrue();
+
+        // Polling doesn't resume immediately; there's a timer.
+        check(async.pendingTimers).length.equals(1);
+        updateMachine.debugAdvanceLoop();
+        async.flushMicrotasks();
+        check(connection.lastRequest).isNull();
+        check(async.pendingTimers).length.equals(1);
+
+        // Polling continues after a timer.
+        connection.prepare(json: GetEventsResult(events: [
+          HeartbeatEvent(id: 2),
+        ], queueId: null).toJson());
+        async.flushTimers();
+        checkLastRequest(lastEventId: 1);
+        check(updateMachine.lastEventId).equals(2);
+        check(store).isLoading.isFalse();
       });
     }
 
     group('retries', () {
-      checkRetry('retries on Server5xxException',
-        () => connection.prepare(httpStatus: 500, body: 'splat'));
+      test('retries on Server5xxException', () =>
+        checkRetry(() => connection.prepare(httpStatus: 500, body: 'splat')));
 
-      checkRetry('retries on NetworkException',
-        () => connection.prepare(exception: Exception("failed")));
+      test('retries on NetworkException', () =>
+        checkRetry(() => connection.prepare(exception: Exception("failed"))));
 
-      checkRetry('retries on ZulipApiException',
-        () => connection.prepare(httpStatus: 400, json: {
-          'result': 'error', 'code': 'BAD_REQUEST', 'msg': 'Bad request'}));
+      test('retries on ZulipApiException', () =>
+        checkRetry(() => connection.prepare(httpStatus: 400, json: {
+            'result': 'error', 'code': 'BAD_REQUEST', 'msg': 'Bad request'}),
+          errorMessage: 'Error loading server data. Will retry'));
 
-      checkRetry('retries on MalformedServerResponseException',
-        () => connection.prepare(httpStatus: 200, body: 'nonsense'));
+      test('retries on MalformedServerResponseException', () =>
+        checkRetry(() => connection.prepare(httpStatus: 200, body: 'nonsense'),
+          errorMessage: 'Error loading server data. Will retry'));
     });
   });