store: Ignore boring NetworkExceptions

Usually when a client goes back from sleep or lose network connection,
there will be a bunch of errors when polling event queue.  This known
error will always be a `NetworkException`, so we make a separate case
for it.

Previously, we may report these errors, and it ended up being spammy.
This filters out the more interesting one to report instead.

Fixes: #555

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

Author: PIG208

lib/model/store.dart

@@ -964,7 +964,7 @@ class UpdateMachine {
             debugLog('… Event queue replaced.');
             return;
 
-          case Server5xxException() || NetworkException():
+          case Server5xxException():
             assert(debugLog('Transient error polling event queue for $store: $e\n'
                 'Backing off, then will retry…'));
             maybeReportTransientError(
@@ -975,6 +975,21 @@ class UpdateMachine {
             assert(debugLog('… Backoff wait complete, retrying poll.'));
             continue;
 
+          case NetworkException():
+            assert(debugLog('Transient error polling event queue for $store: $e\n'
+                'Backing off, then will retry…'));
+            if (e.cause is! SocketException) {
+              // Heuristic check to only report interesting errors to the user.
+              // A [SocketException] is common when the app returns from sleep.
+              maybeReportTransientError(
+                localizations.errorConnectingToServerShort,
+                details: localizations.errorConnectingToServerDetails(
+                  serverUrl, e.toString()));
+            }
+            await (backoffMachine ??= BackoffMachine()).wait();
+            assert(debugLog('… Backoff wait complete, retrying poll.'));
+            continue;
+
           default:
             assert(debugLog('Error polling event queue for $store: $e\n'
                 'Backing off and retrying even though may be hopeless…'));

test/model/store_test.dart

@@ -1,4 +1,5 @@
 import 'dart:async';
+import 'dart:io';
 
 import 'package:checks/checks.dart';
 import 'package:fake_async/fake_async.dart';
@@ -717,6 +718,24 @@ void main() {
           "Error connecting to Zulip. Retrying…\n"
           "Error connecting to Zulip at");
       }));
+
+      test('ignore boring errors', () => awaitFakeAsync((async) async {
+        await prepare();
+
+        for (int i = 0; i < UpdateMachine.transientFailureCountNotifyThreshold; i++) {
+          connection.prepare(exception: const SocketException('failed'));
+          pollAndFail(async);
+          check(takeLastReportedError()).isNull();
+          // This skips the pending polling backoff.
+          async.flushTimers();
+        }
+
+        connection.prepare(exception: const SocketException('failed'));
+        pollAndFail(async);
+        // Normally we start showing user visible error messages for transient
+        // errors after enough number of retries.
+        check(takeLastReportedError()).isNull();
+      }));
     });
   });