feat: Implement RateLimiter into enroll_verb_handler and add unit test

packages/at_secondary_server/config/config.yaml

@@ -154,4 +154,8 @@ testing:
 enrollment:
   # The maximum time in hours for an enrollment to expire, beyond which any action on enrollment is forbidden.
   # Default values is 48 hours.
-  expiryInHours: 48
+  expiryInHours: 48
+  # The maximum number of requests allowed within the time window.
+  maxRequestsPerTimeFrame: 5
+  # The duration of the time window in hours.
+  timeFrameInHours: 1

packages/at_secondary_server/lib/src/connection/inbound/dummy_inbound_connection.dart

@@ -1,12 +1,19 @@
 import 'dart:io';
 
 import 'package:at_secondary/src/connection/inbound/inbound_connection_metadata.dart';
+import 'package:at_secondary/src/server/at_secondary_config.dart';
 import 'package:at_server_spec/at_server_spec.dart';
 
 /// A dummy implementation of [InboundConnection] class which returns a dummy inbound connection.
 class DummyInboundConnection implements InboundConnection {
   var metadata = InboundConnectionMetadata();
 
+  @override
+  int maxRequestsPerTimeFrame = AtSecondaryConfig.maxEnrollRequestsAllowed;
+
+  @override
+  int timeFrameInMillis = AtSecondaryConfig.timeFrameInMills;
+
   @override
   void acceptRequests(Function(String p1, InboundConnection p2) callback,
       Function(List<int>, InboundConnection) streamCallback) {}
@@ -54,4 +61,9 @@ class DummyInboundConnection implements InboundConnection {
 
   @override
   Socket? receiverSocket;
+
+  @override
+  bool isRequestAllowed() {
+    return true;
+  }
 }

packages/at_secondary_server/lib/src/connection/inbound/inbound_connection_impl.dart

@@ -1,10 +1,12 @@
+import 'dart:collection';
 import 'dart:io';
 import 'dart:math';
 
 import 'package:at_secondary/src/connection/base_connection.dart';
 import 'package:at_secondary/src/connection/inbound/inbound_connection_metadata.dart';
 import 'package:at_secondary/src/connection/inbound/inbound_connection_pool.dart';
 import 'package:at_secondary/src/connection/inbound/inbound_message_listener.dart';
+import 'package:at_secondary/src/server/at_secondary_config.dart';
 import 'package:at_secondary/src/server/server_context.dart';
 import 'package:at_secondary/src/server/at_secondary_impl.dart';
 import 'package:at_secondary/src/utils/logging_util.dart';
@@ -42,6 +44,17 @@ class InboundConnectionImpl extends BaseConnection
   late double lowWaterMarkRatio;
   late bool progressivelyReduceAllowableInboundIdleTime;
 
+  /// The maximum number of requests allowed within the specified time frame.
+  @override
+  late int maxRequestsPerTimeFrame;
+
+  /// The duration of the time frame within which requests are limited.
+  @override
+  late int timeFrameInMillis;
+
+  /// A list of timestamps representing the times when requests were made.
+  late final Queue<int> requestTimestampQueue;
+
   InboundConnectionImpl(Socket? socket, String? sessionId, {this.owningPool})
       : super(socket) {
     metaData = InboundConnectionMetadata()
@@ -69,6 +82,10 @@ class InboundConnectionImpl extends BaseConnection
         secondaryContext.authenticatedInboundIdleTimeMillis;
     authenticatedMinAllowableIdleTimeMillis =
         secondaryContext.authenticatedMinAllowableIdleTimeMillis;
+
+    maxRequestsPerTimeFrame = AtSecondaryConfig.maxEnrollRequestsAllowed;
+    timeFrameInMillis = AtSecondaryConfig.timeFrameInMills;
+    requestTimestampQueue = Queue();
   }
 
   /// Returns true if the underlying socket is not null and socket's remote address and port match.
@@ -230,4 +247,31 @@ class InboundConnectionImpl extends BaseConnection
           metaData, 'SENT: ${BaseConnection.truncateForLogging(data)}'));
     }
   }
+
+  @override
+  bool isRequestAllowed() {
+    int currentTimeInMills = DateTime.now().toUtc().millisecondsSinceEpoch;
+    _checkAndUpdateQueue(currentTimeInMills);
+    if (requestTimestampQueue.length < maxRequestsPerTimeFrame) {
+      requestTimestampQueue.addLast(currentTimeInMills);
+      return true;
+    }
+    return false;
+  }
+
+  /// Checks and updates the request timestamp queue based on the current time.
+  ///
+  /// This method removes timestamps from the queue that are older than the specified
+  /// time window.
+  ///
+  /// [currentTimeInMillis] is the current time in milliseconds since epoch.
+  void _checkAndUpdateQueue(int currentTimeInMillis) {
+    if (requestTimestampQueue.isEmpty) return;
+    int calculatedTime = (currentTimeInMillis - requestTimestampQueue.first);
+    while (calculatedTime >= timeFrameInMillis) {
+      requestTimestampQueue.removeFirst();
+      if (requestTimestampQueue.isEmpty) break;
+      calculatedTime = (currentTimeInMillis - requestTimestampQueue.first);
+    }
+  }
 }

packages/at_secondary_server/lib/src/exception/global_exception_handler.dart

@@ -68,7 +68,8 @@ class GlobalExceptionHandler {
         exception is KeyNotFoundException ||
         exception is AtConnectException ||
         exception is SocketException ||
-        exception is AtTimeoutException) {
+        exception is AtTimeoutException ||
+        exception is AtThrottleLimitExceeded) {
       logger.info(exception.toString());
       await _sendResponseForException(exception, atConnection);
     } else if (exception is InternalServerError) {

packages/at_secondary_server/lib/src/server/at_secondary_config.dart

@@ -121,12 +121,22 @@ class AtSecondaryConfig {
           ? ConfigUtil.getPubspecConfig()!['version']
           : null;
 
-  static final int _enrollmentExpiryInHours = 48;
-
   static final Map<String, String> _envVars = Platform.environment;
 
   static String? get secondaryServerVersion => _secondaryServerVersion;
 
+  // Enrollment Configurations
+  static const int _enrollmentExpiryInHours = 48;
+  static int _maxEnrollRequestsAllowed = 5;
+
+  static final int _timeFrameInHours = 1;
+
+  // For easy of testing, duration in hours is long. Hence introduced "timeFrameInMills"
+  // to have a shorter time frame. This is defaulted to "_timeFrameInHours", can be modified
+  // via the config verb
+  static int _timeFrameInMills =
+      Duration(hours: _timeFrameInHours).inMilliseconds;
+
   static int get enrollmentExpiryInHours => _enrollmentExpiryInHours;
 
   // TODO: Medium priority: Most (all?) getters in this class return a default value but the signatures currently
@@ -716,6 +726,54 @@ class AtSecondaryConfig {
     }
   }
 
+  static int get maxEnrollRequestsAllowed {
+    // For easy of testing purpose, we need to reduce the number of requests.
+    // So, in testing mode, enable to modify the "maxEnrollRequestsAllowed"
+    // can be set via the config verb
+    // Defaults to value in config.yaml
+    if (testingMode) {
+      return _maxEnrollRequestsAllowed;
+    }
+    var result = _getIntEnvVar('maxEnrollRequestsAllowed');
+    if (result != null) {
+      return result;
+    }
+    try {
+      return getConfigFromYaml(['enrollment', 'maxRequestsPerTimeFrame']);
+    } on ElementNotFoundException {
+      return _maxEnrollRequestsAllowed;
+    }
+  }
+
+  static set maxEnrollRequestsAllowed(int value) {
+    _maxEnrollRequestsAllowed = value;
+  }
+
+  static int get timeFrameInMills {
+    // For easy of testing purpose, we need to reduce the time frame.
+    // So, in testing mode, enable to modify the "timeFrameInMills"
+    // can be set via the config verb
+    // Defaults to value in config.yaml
+    if (testingMode) {
+      return _timeFrameInMills;
+    }
+    var result = _getIntEnvVar('enrollTimeFrameInHours');
+    if (result != null) {
+      return Duration(hours: result).inMilliseconds;
+    }
+    try {
+      return Duration(
+              hours: getConfigFromYaml(['enrollment', 'timeFrameInHours']))
+          .inMilliseconds;
+    } on ElementNotFoundException {
+      return Duration(hours: _timeFrameInHours).inMilliseconds;
+    }
+  }
+
+  static set timeFrameInMills(int timeWindowInMills) {
+    _timeFrameInMills = timeWindowInMills;
+  }
+
   //implementation for config:set. This method returns a data stream which subscribers listen to for updates
   static Stream<dynamic>? subscribe(ModifiableConfigs configName) {
     if (testingMode) {
@@ -786,6 +844,10 @@ class AtSecondaryConfig {
         return false;
       case ModifiableConfigs.doCacheRefreshNow:
         return false;
+      case ModifiableConfigs.maxRequestsPerTimeFrame:
+        return maxEnrollRequestsAllowed;
+      case ModifiableConfigs.timeFrameInMills:
+        return Duration(hours: _timeFrameInHours).inMilliseconds;
     }
   }
 
@@ -866,7 +928,9 @@ enum ModifiableConfigs {
   maxNotificationRetries,
   checkCertificateReload,
   shouldReloadCertificates,
-  doCacheRefreshNow
+  doCacheRefreshNow,
+  maxRequestsPerTimeFrame,
+  timeFrameInMills
 }
 
 class ModifiableConfigurationEntry {

packages/at_secondary_server/lib/src/server/at_secondary_impl.dart

@@ -421,6 +421,14 @@ class AtSecondaryServerImpl implements AtSecondaryServer {
         notificationResourceManager.setMaxRetries(newCount);
         QueueManager.getInstance().setMaxRetries(newCount);
       });
+
+      AtSecondaryConfig.subscribe(ModifiableConfigs.maxRequestsPerTimeFrame)?.listen((maxEnrollRequestsAllowed) {
+        AtSecondaryConfig.maxEnrollRequestsAllowed = maxEnrollRequestsAllowed;
+      });
+
+      AtSecondaryConfig.subscribe(ModifiableConfigs.timeFrameInMills)?.listen((timeWindowInMills) {
+        AtSecondaryConfig.timeFrameInMills = timeWindowInMills;
+      });
     }
   }
 

packages/at_secondary_server/lib/src/verb/handler/enroll_verb_handler.dart

@@ -105,11 +105,17 @@ class EnrollVerbHandler extends AbstractVerbHandler {
   /// and its corresponding state.
   ///
   /// Throws "AtEnrollmentException", if the OTP provided is invalid.
+  /// Throws [AtThrottleLimitExceeded], if the number of requests exceed within
+  /// a time window.
   Future<void> _handleEnrollmentRequest(
       EnrollParams enrollParams,
       currentAtSign,
       Map<dynamic, dynamic> responseJson,
       InboundConnection atConnection) async {
+    if (!atConnection.isRequestAllowed()) {
+      throw AtThrottleLimitExceeded(
+          'Enrollment requests have exceeded the limit within the specified time frame');
+    }
     if (!atConnection.getMetaData().isAuthenticated) {
       var otp = enrollParams.otp;
       if (otp == null ||

packages/at_secondary_server/pubspec.yaml

@@ -22,7 +22,7 @@ dependencies:
   at_utils: 3.0.15
   at_chops: 1.0.4
   at_lookup: 3.0.40
-  at_server_spec: 3.0.14
+  at_server_spec: 3.0.15
   at_persistence_spec: 2.0.14
   at_persistence_secondary_server: 3.0.57
   expire_cache: ^2.0.1

packages/at_secondary_server/test/inbound_connection_impl_test.dart

@@ -0,0 +1,44 @@
+import 'dart:io';
+
+import 'package:at_secondary/src/connection/inbound/inbound_connection_impl.dart';
+import 'package:at_server_spec/at_server_spec.dart';
+import 'package:test/test.dart';
+
+void main(){
+  group('A test to verify the rate limiter on inbound connection', () {
+    test('A test to verify requests exceeding the limit are rejected', () {
+      Socket? dummySocket;
+      AtConnection connection1 = InboundConnectionImpl(dummySocket, 'aaa');
+      (connection1 as InboundConnectionImpl).maxRequestsPerTimeFrame = 1;
+      connection1.timeFrameInMillis =
+          Duration(milliseconds: 10).inMilliseconds;
+      expect(connection1.isRequestAllowed(), true);
+      expect(connection1.isRequestAllowed(), false);
+    });
+
+    test('A test to verify requests after the time window are accepted',
+            () async {
+          Socket? dummySocket;
+          AtConnection connection1 = InboundConnectionImpl(dummySocket, 'aaa');
+          (connection1 as InboundConnectionImpl).maxRequestsPerTimeFrame = 1;
+          connection1.timeFrameInMillis = Duration(milliseconds: 2).inMilliseconds;
+          expect(connection1.isRequestAllowed(), true);
+          expect(connection1.isRequestAllowed(), false);
+          await Future.delayed(Duration(milliseconds: 2));
+          expect(connection1.isRequestAllowed(), true);
+        });
+
+    test('A test to verify request from different connection is allowed', () {
+      Socket? dummySocket;
+      AtConnection connection1 = InboundConnectionImpl(dummySocket, 'aaa');
+      AtConnection connection2 = InboundConnectionImpl(dummySocket, 'aaa');
+      (connection1 as InboundConnectionImpl).maxRequestsPerTimeFrame = 1;
+      (connection2 as InboundConnectionImpl).maxRequestsPerTimeFrame = 1;
+      connection1.timeFrameInMillis =
+          Duration(milliseconds: 10).inMilliseconds;
+      expect(connection1.isRequestAllowed(), true);
+      expect(connection1.isRequestAllowed(), false);
+      expect(connection2.isRequestAllowed(), true);
+    });
+  });
+}

tests/at_functional_test/pubspec.yaml

@@ -16,7 +16,7 @@ dependencies:
       ref: trunk
   at_chops: ^1.0.1
   at_lookup: ^3.0.32
-  at_commons: ^3.0.53
+  at_commons: ^3.0.55
   uuid: ^3.0.7
   elliptic: ^0.3.8