Add sinks to provide synchronous access to events.

lib/src/string_accumulator_sink.dart

Index: lib/src/string_accumulator_sink.dart
diff --git a/lib/src/string_accumulator_sink.dart b/lib/src/string_accumulator_sink.dart
new file mode 100644
index 0000000000000000000000000000000000000000..6d8ad566e5b9d627a4d24f20a5fbebf07854a6d0
--- /dev/null
+++ b/lib/src/string_accumulator_sink.dart
@@ -0,0 +1,38 @@
+// Copyright (c) 2016, 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.
+
+import 'dart:convert';
+
+/// A sink that provides synchronous access to the concatenated strings passed

[Lasse Reichstein Nielsen, 2016/04/22 09:15:14]

Again, no need for "synchronous".

[nweiz, 2016/04/22 21:19:56]

Done.

+/// to it.
+class StringAccumulatorSink extends StringConversionSinkBase {
+  /// The string accumulated so far.
+  String get string => _buffer.toString();
+  final _buffer = new StringBuffer();
+
+  /// Whether [close] has been called.
+  bool get isClosed => _isClosed;
+  var _isClosed = false;
+
+  void add(String chunk) {
+    if (_isClosed) {
+      throw new StateError("Can't add to a closed sink.");
+    }
+
+    _buffer.write(chunk);
+  }
+
+  void addSlice(String chunk, int start, int end, bool isLast) {
+    if (_isClosed) {
+      throw new StateError("Can't add to a closed sink.");
+    }
+
+    _buffer.write(chunk.substring(start, end));
+    if (isLast) _isClosed = true;
+  }
+
+  void close() {
+    _isClosed = true;
+  }
+}