store: Report if transient polling errors persist.

Signed-off-by: Zixuan James Li <[email protected]>

Author: PIG208

assets/l10n/app_en.arb

@@ -167,6 +167,13 @@
       "error": {"type": "String", "example": "Invalid format"}
     }
   },
+  "errorConnectingToServer": "Failed to reach server. Will retry:\n\n{error}",
+  "@errorConnectingToServer": {
+    "description": "Dialog message when the the server cannot be reached",
+    "placeholders": {
+      "error": {"type": "String", "example": "Network request failed: HTTP status 500"}
+    }
+  },
   "errorSharingFailed": "Sharing failed",
   "@errorSharingFailed": {
     "description": "Error message when sharing a message failed."

lib/model/store.dart

@@ -767,6 +767,8 @@ class UpdateMachine {
 
   void poll() async {
     BackoffMachine? backoffMachine;
+    int accumulatedTransientFailureCount = 0;
+    const transientFailureCountNotifyThreshold = 5;
 
     while (true) {
       if (_debugLoopSignal != null) {
@@ -795,8 +797,12 @@ class UpdateMachine {
           case Server5xxException() || NetworkException():
             assert(debugLog('Transient error polling event queue for $store: $e\n'
                 'Backing off, then will retry…'));
-            // TODO tell user if transient polling errors persist
             // TODO reset to short backoff eventually
+            accumulatedTransientFailureCount++;
+            if (accumulatedTransientFailureCount > transientFailureCountNotifyThreshold) {
+              reportErrorToUserInDialog(
+                localizations.errorConnectingToServer(e.toString()));
+            }
             await (backoffMachine ??= BackoffMachine()).wait();
             assert(debugLog('… Backoff wait complete, retrying poll.'));
             continue;
@@ -830,6 +836,7 @@ class UpdateMachine {
       // and failures, the successes themselves should space out the requests.
       backoffMachine = null;
       store.isLoading = false;
+      accumulatedTransientFailureCount = 0;
 
       final events = result.events;
       for (final event in events) {

test/model/store_test.dart

@@ -430,25 +430,32 @@ void main() {
 
     void checkRetry(void Function() prepareError, {
       String? errorMessage,
+      int failureCountNofityThreshold = 0,
     }) {
       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);
+        for (int i = 0; i < failureCountNofityThreshold + 1; i++) {
+          // Make the request, inducing an error in it.
+          prepareError();
+          if (i > 0) {
+            // End polling backoff from the previous iteration.
+            async.flushTimers();
+          }
+          updateMachine.debugAdvanceLoop();
+          check(debugLastReportedError).isNull();
+          async.elapse(Duration.zero);
+          if (i < failureCountNofityThreshold || errorMessage == null) {
+            check(debugTakeLastReportedError()).isNull();
+          } else {
+            check(debugTakeLastReportedError()).isNotNull().contains(errorMessage);
+          }
+          checkLastRequest(lastEventId: 1);
+          check(store).isLoading.isTrue();
         }
-        checkLastRequest(lastEventId: 1);
-        check(store).isLoading.isTrue();
 
         // Polling doesn't resume immediately; there's a timer.
         check(async.pendingTimers).length.equals(1);
@@ -469,11 +476,15 @@ void main() {
     }
 
     group('retries', () {
-      test('retries on Server5xxException', () =>
-        checkRetry(() => connection.prepare(httpStatus: 500, body: 'splat')));
-
-      test('retries on NetworkException', () =>
-        checkRetry(() => connection.prepare(exception: Exception("failed"))));
+      test('too many retries on Server5xxException', () =>
+        checkRetry(() => connection.prepare(httpStatus: 500, body: 'splat'),
+          errorMessage: 'Failed to reach server. Will retry',
+          failureCountNofityThreshold: 5));
+
+      test('too many retries on NetworkException', () =>
+        checkRetry(() => connection.prepare(exception: Exception("failed")),
+          errorMessage: 'Failed to reach server. Will retry',
+          failureCountNofityThreshold: 5));
 
       test('retries on ZulipApiException', () =>
         checkRetry(() => connection.prepare(httpStatus: 400, json: {