Updated README to notify users of Dart SDK version requirements.

lib/src/line_decoder.dart

+// Copyright (c) 2017, 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.
+
+part of sync.http;
+
+// '\n' character
+const int _lineTerminator = 10;
+
+typedef void _LineDecoderCallback(
+    String line, int bytesRead, _LineDecoder decoder);
+
+class _LineDecoder {
+  BytesBuilder _unprocessedBytes = new BytesBuilder();
+
+  int expectedByteCount = -1;
+
+  final _LineDecoderCallback _callback;
+
+  _LineDecoder.withCallback(this._callback);
+
+  void add(List<int> chunk) {
+    while (chunk.isNotEmpty) {
+      int splitIndex = -1;
+
+      if (expectedByteCount > 0) {
+        splitIndex = expectedByteCount - _unprocessedBytes.length;
+      } else {
+        splitIndex = chunk.indexOf(_lineTerminator) + 1;
+      }
+
+      if (splitIndex > 0 && splitIndex <= chunk.length) {
+        _unprocessedBytes.add(chunk.sublist(0, splitIndex));
+        chunk = chunk.sublist(splitIndex);
+        expectedByteCount = -1;
+        _process(_unprocessedBytes.takeBytes());
+      } else {
+        _unprocessedBytes.add(chunk);
+        chunk = [];
+      }
+    }
+  }
+
+  void _process(List<int> line) =>
+      _callback(UTF8.decoder.convert(line), line.length, this);
+
+  int get bufferedBytes => _unprocessedBytes.length;
+
+  void close() => _process(_unprocessedBytes.takeBytes());
+}