Add IOSink:flush().

sdk/lib/io/io_sink.dart

 // Copyright (c) 2013, 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 dart.io;
 
 /**
  * Helper class to wrap a [StreamConsumer<List<int>>] and provide
  * utility functions for writing to the StreamConsumer directly. The
  * [IOSink] buffers the input given by all [StringSink] methods and will delay
@@ skipping 28 matching lines @@
    * Writes an error to the consumer.
    */
   void addError(error, [StackTrace stackTrace]);
 
   /**
    * Adds all elements of the given [stream] to `this`.
    */
   Future addStream(Stream<List<int>> stream);
 
   /**
+   * Returns a [Future] that completes once all buffered data is accepted by the
+   * to underlying [StreamConsumer].
+   *
+   * It's an error to call this method, while an [addStream] is incomplete.
+   *
+   * NOTE: This is not necessarily the same as the data being flushed by the
+   * operating system.
+   */
+  Future flush();
+
+  /**
    * Close the target.
    */
   Future close();
 
   /**
    * Get a future that will complete when all synchronous have completed, or an
    * error happened. This future is identical to the future returned from close.
    */
   Future get done;
 }
@@ skipping 33 matching lines @@
           .whenComplete(() {
             _isBound = false;
           });
     }
     if (_controllerInstance == null) return targetAddStream();
     var future = _controllerCompleter.future;
     _controllerInstance.close();
     return future.then((_) => targetAddStream());
   }
 
+  Future flush() {
+    // Adding an empty stream-controller will return a future that will complete
+    // when all data is done.
+    var controller = new StreamController()..close();
+    return addStream(controller.stream).then((_) => this);
+  }
+
   Future close() {
     if (_isBound) {
       throw new StateError("StreamSink is bound to a stream");
     }
     if (!_isClosed) {
       _isClosed = true;
       if (_controllerInstance != null) {
         _controllerInstance.close();
       } else {
         _closeTarget();
@@ skipping 113 matching lines @@
 
   void writeln([Object obj = ""]) {
     write(obj);
     write("\n");
   }
 
   void writeCharCode(int charCode) {
     write(new String.fromCharCode(charCode));
   }
 }