Minimalistic analytics library used by Dart Server and try.dartlang.org

dart/pkg/microlytics/lib/channels.dart

+// Copyright (c) 2014, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+library microlytics.channels;
+
+import 'dart:async';
+
+const String ANALYTICS_URL = "https://ssl.google-analytics.com/collect";
+
+abstract class Channel {
+  void sendData(String data);
+  void shutdown() {}
+}
+
+/// [Channel] that implements a leaky bucket
+/// algorithm to provide rate limiting.
+/// See [http://en.wikipedia.org/wiki/Leaky_bucket].
+class RateLimitingBufferedChannel extends Channel {
+  final List<String> _buffer = <String>[];
+  final Channel _innerChannel;
+  final int _bufferSizeLimit;
+  Timer _timer;
+
+  RateLimitingBufferedChannel(
+      this._innerChannel,
+      {int bufferSizeLimit: 10,
+        double packetsPerSecond: 1.0})
+      : this._bufferSizeLimit = bufferSizeLimit {
+    if (!(packetsPerSecond > 0)) {
+      throw new ArgumentError("packetsPerSecond must be larger than zero.");
+    }
+
+    int transmitDelay = (1000 / packetsPerSecond).floor();
+    _timer = new Timer.periodic(
+        new Duration(milliseconds: transmitDelay), _onTimerTick);
+  }
+
+  void _onTimerTick(_) {
+    if (_buffer.length > 0) {
+      String item = _buffer.removeLast();
+      _innerChannel.sendData(item);
+    }
+  }
+
+  void sendData(String data) {
+    if (_buffer.length >= _bufferSizeLimit) return;
+    _buffer.add(data);
+  }
+
+  void shutdown() {
+    _timer.cancel();
+    _innerChannel.shutdown();
+  }
+}