Convert json_rpc.Server to take a Stream and StreamSink.

pkg/json_rpc_2/lib/src/utils.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 json_rpc_2.utils;
 
 import 'dart:async';
 
 import 'package:stack_trace/stack_trace.dart';
 
@@ skipping 25 matching lines @@
 /// A regular expression to match the exception prefix that some exceptions'
 /// [Object.toString] values contain.
 final _exceptionPrefix = new RegExp(r'^([A-Z][a-zA-Z]*)?(Exception|Error): ');
 
 /// Get a string description of an exception.
 ///
 /// Many exceptions include the exception class name at the beginning of their
 /// [toString], so we remove that if it exists.
 String getErrorMessage(error) =>
     error.toString().replaceFirst(_exceptionPrefix, '');
+
+/// Returns a [StreamSink] that wraps [sink] and maps each event added using
+/// [callback].
+StreamSink mapStreamSink(StreamSink sink, callback(event)) =>
+    new _MappedStreamSink(sink, callback);
+
+/// A [StreamSink] wrapper that maps each event added to the sink.
+class _MappedStreamSink implements StreamSink {
+  final StreamSink _inner;
+  final Function _callback;
+
+  Future get done => _inner.done;
+
+  _MappedStreamSink(this._inner, this._callback);
+
+  void add(event) => _inner.add(_callback(event));
+  void addError(error, [StackTrace stackTrace]) =>
+      _inner.addError(error, stackTrace);
+  Future addStream(Stream stream) => _inner.addStream(stream.map(_callback));
+  Future close() => _inner.close();
+}