Dart: Adds a content handler and a test.

mojo/public/dart/src/drain_data.dart

Index: mojo/public/dart/src/drain_data.dart
diff --git a/mojo/public/dart/src/drain_data.dart b/mojo/public/dart/src/drain_data.dart
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+++ b/mojo/public/dart/src/drain_data.dart
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+// Copyright 2014 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+part of core;
+
+class DataPipeDrainer {
+  MojoDataPipeConsumer _consumer;
+  MojoEventStream _eventStream;
+  List<ByteData> _dataList;
+  int _dataSize;
+
+  DataPipeDrainer(this._consumer) {
+    _eventStream = new MojoEventStream(_consumer.handle);
+    _dataList = new List();
+    _dataSize = 0;
+  }
+
+  MojoResult _doRead() {
+    ByteData thisRead = _consumer.beginRead();
+    if (thisRead == null) {
+      throw 'Data pipe beginRead failed: ${_consumer.status}';
+    }
+    _dataList.add(thisRead);
+    _dataSize += thisRead.lengthInBytes;
+    return _consumer.endRead(thisRead.lengthInBytes);
+  }
+
+  ByteData _concatData() {
+    var data = new ByteData(_dataSize);
+    int end = 0;
+    for (var chunk in _dataList) {
+      data.buffer.asUint8List().setRange(
+          end, end + chunk.lengthInBytes, chunk.buffer.asUint8List());
+      end += chunk.lengthInBytes;
+    }
+    return data;
+  }
+
+  Future<ByteData> drain() {
+    var completer = new Completer();
+    _eventStream.listen((List<int> event) {
+      var mojoSignals = new MojoHandleSignals(event[1]);
+      if (mojoSignals.isReadable) {
+        var result = _doRead();
+        if (!result.isOk) {
+          _eventStream.close();
+          _eventStream = null;
+          completer.complete(_concatData());
+        } else {
+          _eventStream.enableReadEvents();
+        }
+      } else if (mojoSignals.isPeerClosed) {
+        _eventStream.close();
+        _eventStream = null;
+        completer.complete(_concatData());
+      } else {
+        throw 'Unexpected handle event: $mojoSignals';
+      }
+    });
+    return completer.future;
+  }
+
+  static Future<ByteData> drainHandle(MojoDataPipeConsumer consumer) {
+    var drainer = new DataPipeDrainer(consumer);
+    return drainer.drain();
+  }
+}