StreamConsumer has an addStream and a close functions.

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>, T>] and provide
  * utility functions for writing to the StreamConsumer directly. The
  * [IOSink] buffers the input given by [write], [writeAll], [writeln],
@@ skipping 19 matching lines @@
    * Writes the bytes uninterpreted to the consumer.
    */
   void writeBytes(List<int> data);
 
   /**
    * Provide functionality for piping to the [IOSink].
    */
   Future<T> consume(Stream<List<int>> stream);
 
   /**
+   * Adds all elements of the given [stream] to `this`.
+   */
+  Future<T> addStream(Stream<List<int>> stream);
+
+  /**
    * Like [consume], but will not close the target when done.
+   *
+   * *Deprecated*: use [addStream] instead.
    */
   Future<T> writeStream(Stream<List<int>> stream);
 
   /**
    * Close the target.
    */
-  void close();
+  // TODO(floitsch): Currently the future cannot be typed because it has
+  // hardcoded type Future<HttpClientResponse> in subclass HttpClientRequest.
+  Future close();
 
   /**
    * Get future that will complete when all data has been written to
    * the IOSink and it has been closed.
    */
   Future<T> get done;
 }
 
 
 class _IOSinkImpl<T> implements IOSink<T> {
@@ skipping 69 matching lines @@
   }
 
   Future<T> consume(Stream<List<int>> stream) {
     if (_isBound) {
       throw new StateError("IOSink is already bound to a stream");
     }
     return _fillFromStream(stream);
   }
 
   Future<T> writeStream(Stream<List<int>> stream) {
+    return addStream(stream);
+  }
+
+  Future<T> addStream(Stream<List<int>> stream) {
     if (_isBound) {
       throw new StateError("IOSink is already bound to a stream");
     }
     return _fillFromStream(stream, unbind: true);
   }
 
-  void close() {
+  Future close() {
     if (_isBound) {
       throw new StateError("IOSink is already bound to a stream");
     }
     _controller.close();
+    return _pipeFuture;
   }
 
   Future<T> get done {
     _controller;
     return _pipeFuture;
   }
 
   void _completeWriteStreamCompleter([error]) {
     if (_writeStreamCompleter == null) return;
     var tmp = _writeStreamCompleter;
@@ skipping 79 matching lines @@
         },
         onError: _controller.addError);
     if (_paused) _pause();
     if (unbind) {
       return _writeStreamCompleter.future;
     } else {
       return _pipeFuture;
     }
   }
 }