Add a Client class to json_rpc_2.

pkg/json_rpc_2/lib/src/server.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.server;
 
 import 'dart:async';
 import 'dart:collection';
 import 'dart:convert';
 
@@ skipping 51 matching lines @@
   ///
   /// If [requests] is a [StreamSink] as well as a [Stream], [responses] may be
   /// omitted.
   ///
   /// Note that the server won't begin listening to [requests] until
   /// [Server.listen] is called.
   Server.withoutJson(Stream requests, [StreamSink responses])
       : _streams = new TwoWayStream.withoutJson(
             "Server", requests, "requests", responses, "responses");
 
+  /// Users of the library should not use this constructor.
+  Server.internal(this._streams);
+
   /// Starts listening to the underlying stream.
   ///
   /// Returns a [Future] that will complete when the stream is closed or when it
   /// has an error.
   ///
   /// [listen] may only be called once.
   Future listen() => _streams.listen(_handleRequest);
 
   /// Closes the server's request subscription and response sink.
   ///
@@ skipping 155 matching lines @@
       return syncFuture(() => iterator.current(params)).catchError((error) {
         if (error is! RpcException) throw error;
         if (error.code != error_code.METHOD_NOT_FOUND) throw error;
         return _tryNext();
       });
     }
 
     return _tryNext();
   }
 }