fix: return topic subscribe error immediately if subscription limit r…

…eached (#62)

* fix: return topic subscribe error immediately if subscription limit reached

* dart format

* remove keepalive settings

* update examples to await subscribe

* dart format

* use env var in flutter app instead of hardcoded api key

* dart format

* flutter app can use fromEnvVar credential provider instead

example/flutter_chat_app/README.md

@@ -8,12 +8,14 @@
 
 ## Running the Flutter Demo App
 
-1. Provide your Momento API key in [`lib/main.dart`](./lib/main.dart) at this line:
-    ```
-    static const String _momentoApiKey = "your-api-key-here";
-    ```
+You can run Flutter apps in [VSCode](https://docs.flutter.dev/tools/vs-code) or [Android Studio or IntelliJ](https://docs.flutter.dev/tools/android-studio) using built-in tooling, just make sure to provide your Momento API key as an environment variable named `MOMENTO_API_KEY`.
 
-2. Run in [VSCode](https://docs.flutter.dev/tools/vs-code) or [Android Studio or IntelliJ](https://docs.flutter.dev/tools/android-studio). If using the command line, you can run using a command like: `flutter run -d <device_id>`. You can use `flutter devices` to see all connected devices and their IDs.
+You can also use the terminal to list your devides and select one to run.
+
+```bash
+flutter devices
+flutter run -d <device_id> --dart-define="MOMENTO_API_KEY=<your-api-key>"
+```
 
 ## Flutter Resources
 

example/flutter_chat_app/lib/main.dart

@@ -1,6 +1,6 @@
 import 'dart:io';
 
-import 'package:client_sdk_dart/momento.dart';
+import 'package:momento/momento.dart';
 import 'package:flutter/material.dart';
 
 void main() {
@@ -33,9 +33,9 @@ class MyHomePage extends StatefulWidget {
 }
 
 class _MyHomePageState extends State<MyHomePage> {
-  static const String _momentoApiKey = "your-api-key-here";
   TopicClient _topicClient = TopicClient(
-      CredentialProvider.fromString(_momentoApiKey), Mobile.latest());
+      CredentialProvider.fromEnvironmentVariable('MOMENTO_API_KEY'),
+      MobileTopicConfiguration.latest());
 
   List<String> _messages = ["Welcome to Momento Topics!"];
   final TextEditingController _textInputController = TextEditingController();
@@ -45,8 +45,12 @@ class _MyHomePageState extends State<MyHomePage> {
   @override
   void initState() {
     super.initState();
+    establishSubscription();
+    return;
+  }
 
-    final subscribeResult = _topicClient.subscribe("cache", "topic");
+  Future<void> establishSubscription() async {
+    final subscribeResult = await _topicClient.subscribe("cache", "topic");
     switch (subscribeResult) {
       case TopicSubscription():
         print("Successful subscription");

example/flutter_chat_app/pubspec.yaml

@@ -18,7 +18,7 @@ environment:
 dependencies:
   flutter:
     sdk: flutter
-  client_sdk_dart:
+  momento:
     path: ../../../client-sdk-dart
 
 

example/topics/advanced.dart

@@ -30,7 +30,7 @@ void main() async {
     }
   });
 
-  var subscription = topicClient.subscribe("cache", "topic");
+  var subscription = await topicClient.subscribe("cache", "topic");
   var messageStream = switch (subscription) {
     TopicSubscription() => subscription.stream,
     TopicSubscribeError() => throw Exception(
@@ -59,7 +59,7 @@ void main() async {
 
   // unsubscribing should not affect the topic client's ability
   // to subscribe to another topic afterwards
-  var sub2 = topicClient.subscribe("cache", "topic");
+  var sub2 = await topicClient.subscribe("cache", "topic");
   switch (sub2) {
     case TopicSubscription():
       print("Successful 2nd subscription!");

example/topics/basic_subscriber.dart

@@ -6,7 +6,7 @@ void main() async {
       CredentialProvider.fromEnvironmentVariable("MOMENTO_API_KEY"),
       TopicClientConfigurations.latest());
 
-  var subscription = topicClient.subscribe("cache", "topic");
+  var subscription = await topicClient.subscribe("cache", "topic");
   var messageStream = switch (subscription) {
     TopicSubscription() => subscription.stream,
     TopicSubscribeError() => throw Exception(

lib/src/internal/pubsub_client.dart

@@ -14,7 +14,7 @@ abstract class AbstractPubsubClient {
   Future<TopicPublishResponse> publish(
       String cacheName, String topicName, Value value);
 
-  TopicSubscribeResponse subscribe(String cacheName, String topicName);
+  Future<TopicSubscribeResponse> subscribe(String cacheName, String topicName);
 
   void close();
 }
@@ -61,20 +61,29 @@ class ClientPubsub implements AbstractPubsubClient {
   }
 
   @override
-  TopicSubscribeResponse subscribe(String cacheName, String topicName,
-      {Int64? resumeAtTopicSequenceNumber}) {
+  Future<TopicSubscribeResponse> subscribe(String cacheName, String topicName,
+      {Int64? resumeAtTopicSequenceNumber}) async {
     var request = SubscriptionRequest_();
     request.cacheName = cacheName;
     request.topic = topicName;
     request.resumeAtTopicSequenceNumber =
         resumeAtTopicSequenceNumber ?? Int64(0);
     try {
       var stream = _grpcManager.client.subscribe(request);
-      return TopicSubscription(stream, request.resumeAtTopicSequenceNumber,
-          this, cacheName, topicName);
+      final subscription = TopicSubscription(stream,
+          request.resumeAtTopicSequenceNumber, this, cacheName, topicName);
+
+      try {
+        await subscription.init();
+        return subscription;
+      } catch (e) {
+        rethrow;
+      }
     } catch (e) {
       if (e is GrpcError) {
         return TopicSubscribeError(grpcStatusToSdkException(e));
+      } else if (e is SdkException) {
+        return TopicSubscribeError(e);
       }
       return TopicSubscribeError(
           UnknownException("Unexpected error: $e", null, null));

lib/src/internal/topics_grpc_manager.dart

@@ -9,11 +9,7 @@ class TopicGrpcManager {
   final _logger = Logger('MomentoTopicClient');
 
   TopicGrpcManager(CredentialProvider credentialProvider) {
-    _channel = ClientChannel(credentialProvider.cacheEndpoint,
-        options: ChannelOptions(
-            keepAlive: ClientKeepAliveOptions(
-                pingInterval: Duration(seconds: 10),
-                timeout: Duration(seconds: 5))));
+    _channel = ClientChannel(credentialProvider.cacheEndpoint);
     _client = PubsubClient(_channel,
         options: CallOptions(metadata: {
           'authorization': credentialProvider.apiKey,

lib/src/messages/responses/topics/topic_subscribe.dart

@@ -18,9 +18,24 @@ class TopicSubscription implements TopicSubscribeResponse {
   String topicName;
   bool retry = true;
   final logger = Logger("TopicSubscribeResponse");
+  late Stream _broadcastStream;
 
   TopicSubscription(this._stream, this.lastSequenceNumber, this._client,
-      this.cacheName, this.topicName);
+      this.cacheName, this.topicName) {
+    _broadcastStream = _stream.asBroadcastStream();
+  }
+
+  Future<void> init() async {
+    await for (final firstItem in _broadcastStream) {
+      if (firstItem.whichKind() != SubscriptionItem__Kind.heartbeat) {
+        throw InternalServerException(
+            "Expected heartbeat message for topic $topicName on cache $cacheName, got ${firstItem.whichKind()}",
+            null,
+            null);
+      }
+      break;
+    }
+  }
 
   Stream<TopicSubscriptionItemResponse> get stream {
     return _handleStream();
@@ -29,7 +44,7 @@ class TopicSubscription implements TopicSubscribeResponse {
   Stream<TopicSubscriptionItemResponse> _handleStream() async* {
     while (retry) {
       try {
-        await for (final msg in _stream) {
+        await for (final msg in _broadcastStream) {
           var result = _processResult(msg);
           if (result != null) {
             yield result;
@@ -39,20 +54,41 @@ class TopicSubscription implements TopicSubscribeResponse {
         if (e is CancelledException ||
             (e is GrpcError && e.codeName == "CANCELLED")) {
           logger.fine("Subscription was cancelled, not reconnecting");
+          await _stream.cancel();
+          retry = false;
+        } else if (e is ClientResourceExhaustedException ||
+            (e is GrpcError && e.codeName == "RESOURCE_EXHAUSTED")) {
+          logger.fine("Subscription limit reached, not reconnecting");
+          await _stream.cancel();
           retry = false;
         } else {
           logger.fine("Attempting to reconnect after receiving error: $e");
-          var result = _client.subscribe(cacheName, topicName,
-              resumeAtTopicSequenceNumber: lastSequenceNumber);
-          if (result is TopicSubscription) {
-            _stream = result._stream;
-            lastSequenceNumber = result.lastSequenceNumber;
-          } else if (result is TopicSubscribeError) {
-            logger.fine("Error reconnecting: ${result.message}");
-          }
         }
       }
+
+      if (retry) {
+        logger.fine("retry is still true");
+        retry = await attemptReconnect();
+      }
+    }
+  }
+
+  Future<bool> attemptReconnect() async {
+    await _stream.cancel();
+    var result = await _client.subscribe(cacheName, topicName,
+        resumeAtTopicSequenceNumber: lastSequenceNumber);
+    if (result is TopicSubscription) {
+      _stream = result._stream;
+      _broadcastStream = result._broadcastStream;
+      lastSequenceNumber = result.lastSequenceNumber;
+    } else if (result is TopicSubscribeError) {
+      logger.fine("Error reconnecting: ${result.message}");
+      if (result.errorCode == MomentoErrorCode.limitExceededError ||
+          result.errorCode == MomentoErrorCode.cancelledError) {
+        return false;
+      }
     }
+    return true;
   }
 
   TopicSubscriptionItemResponse? _processResult(SubscriptionItem_ item) {

lib/src/topic_client.dart

@@ -10,7 +10,7 @@ abstract class ITopicClient {
   Future<TopicPublishResponse> publish(
       String cacheName, String topicName, Value value);
 
-  TopicSubscribeResponse subscribe(String cacheName, String topicName);
+  Future<TopicSubscribeResponse> subscribe(String cacheName, String topicName);
 
   void close();
 }
@@ -33,8 +33,9 @@ class TopicClient implements ITopicClient {
   }
 
   @override
-  TopicSubscribeResponse subscribe(String cacheName, String topicName) {
-    return _pubsubClient.subscribe(cacheName, topicName);
+  Future<TopicSubscribeResponse> subscribe(
+      String cacheName, String topicName) async {
+    return await _pubsubClient.subscribe(cacheName, topicName);
   }
 
   @override

pubspec.yaml

@@ -14,7 +14,7 @@ dependencies:
   logging: ^1.2.0
   protobuf: ^3.1.0
   string_validator: ^1.0.2
-  uuid: ^4.3.1
+  uuid: ^4.2.2
   # path: ^1.8.0
 
 dev_dependencies: