Add a Client class to json_rpc_2.

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 26 matching lines @@
 /// [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, '');
 
+/// Like `try`/`finally`, run [body] and ensure that [whenComplete] runs
+/// afterwards, regardless of whether [body] succeeded.
+///
+/// This is synchronicity-agnostic relative to [body]. If [body] returns a
+/// [Future], this wil run asynchronously; otherwise it will run synchronously.
+tryFinally(body(), whenComplete()) {
+  var result;
+  try {
+    result = body();
+  } catch (_) {
+    whenComplete();
+    rethrow;
+  }
+
+  if (result is! Future) {
+    whenComplete();
+    return result;
+  } else {
+    return result.whenComplete(whenComplete);
+  }
+}
+
 /// 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();
 }