feat: apply sample rate

dart/lib/src/client.dart

@@ -1,4 +1,5 @@
 import 'dart:async';
+import 'dart:math';
 
 import 'package:meta/meta.dart';
 import 'package:sentry/sentry.dart';
@@ -17,13 +18,16 @@ abstract class SentryClient {
   /// `dart:html` is available, otherwise it will throw an unsupported error.
   factory SentryClient(SentryOptions options) => createSentryClient(options);
 
-  SentryClient.base(this.options, {@required this.transport});
+  SentryClient.base(this.options, {@required this.transport}) {
+    _random = options.sampleRate == null ? null : Random();
+  }
 
   @protected
   SentryOptions options;
 
+  // TODO: this should be removed and used options.transport
   @visibleForTesting
-  final Transport transport;
+  Transport transport;
 
   /// Information about the current user.
   ///
@@ -37,6 +41,8 @@ abstract class SentryClient {
   /// * https://docs.sentry.io/learn/context/#capturing-the-user
   User userContext;
 
+  Random _random;
+
   /// Reports an [event] to Sentry.io.
   Future<SentryId> captureEvent(
     SentryEvent event, {
@@ -45,6 +51,11 @@ abstract class SentryClient {
   }) async {
     event = _processEvent(event, eventProcessors: options.eventProcessors);
 
+    // dropped by sampling or event processors
+    if (event == null) {
+      return Future.value(SentryId.empty());
+    }
+
     event = _applyScope(event: event, scope: scope);
 
     event = event.copyWith(
@@ -97,6 +108,14 @@ abstract class SentryClient {
     dynamic hint,
     List<EventProcessor> eventProcessors,
   }) {
+    if (_sampleRate()) {
+      options.logger(
+        SentryLevel.debug,
+        'Event ${event.eventId.toString()} was dropped due to sampling decision.',
+      );
+      return null;
+    }
+
     for (final processor in eventProcessors) {
       try {
         event = processor(event, hint);
@@ -157,4 +176,11 @@ abstract class SentryClient {
     }
     return event;
   }
+
+  bool _sampleRate() {
+    if (options.sampleRate != null && _random != null) {
+      return (options.sampleRate < _random.nextDouble());
+    }
+    return true;
+  }
 }

dart/lib/src/sentry_options.dart

@@ -102,8 +102,8 @@ class SentryOptions {
 
   /// Configures the sample rate as a percentage of events to be sent in the range of 0.0 to 1.0. if
   /// 1.0 is set it means that 100% of events are sent. If set to 0.1 only 10% of events will be
-  /// sent. Events are picked randomly. Default is 1.0 (disabled)
-  double sampleRate = 1.0;
+  /// sent. Events are picked randomly. Default is null (disabled)
+  double sampleRate;
 
   /// A list of string prefixes of module names that do not belong to the app, but rather third-party
   /// packages. Modules considered not to be part of the app will be hidden from stack traces by
@@ -119,6 +119,14 @@ class SentryOptions {
   List<String> get inAppIncludes => List.unmodifiable(_inAppIncludes);
 
   // TODO: transport, transportGate, connectionTimeoutMillis, readTimeoutMillis, hostnameVerifier, sslSocketFactory, proxy
+  Transport _transport;
+
+  Transport get transport => _transport;
+
+  set transport(Transport transport) {
+    // TODO: NoOp transport
+    _transport = transport;
+  }
 
   /// Sets the distribution. Think about it together with release and environment
   String dist;

dart/test/mocks.dart

@@ -4,6 +4,8 @@ import 'package:sentry/src/protocol.dart';
 
 class MockSentryClient extends Mock implements SentryClient {}
 
+class MockTransport extends Mock implements Transport {}
+
 final fakeDsn = 'https://[email protected]/1234567';
 
 final fakeException = Exception('Error');

dart/test/sentry_client_test.dart

@@ -0,0 +1,44 @@
+import 'package:mockito/mockito.dart';
+import 'package:sentry/sentry.dart';
+import 'package:test/test.dart';
+
+import 'mocks.dart';
+
+void main() {
+  group('SentryClient sampling', () {
+    SentryOptions options;
+    Transport transport;
+
+    setUp(() {
+      options = SentryOptions(dsn: fakeDsn);
+      transport = MockTransport();
+    });
+
+    test('captures event, sample rate is 100% enabled', () {
+      options.sampleRate = 1.0;
+      final client = SentryClient(options);
+      client.transport = transport;
+      client.captureEvent(fakeEvent);
+
+      verify(client.transport.send(any)).called(1);
+    });
+
+    test('do not capture event, sample rate is 0% disabled', () {
+      options.sampleRate = 0.0;
+      final client = SentryClient(options);
+      client.transport = transport;
+      client.captureEvent(fakeEvent);
+
+      verifyNever(client.transport.send(any));
+    });
+
+    test('do not capture event, sample rate is null', () {
+      options.sampleRate = null;
+      final client = SentryClient(options);
+      client.transport = transport;
+      client.captureEvent(fakeEvent);
+
+      verifyNever(client.transport.send(any));
+    });
+  });
+}