Implement onClosed on a socket output stream

runtime/bin/socket_stream_impl.dart

 // Copyright (c) 2012, 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.
 
 class _SocketInputStream implements SocketInputStream {
   _SocketInputStream(Socket socket) : _socket = socket {
     if (_socket._id == -1) _closed = true;
     _socket.onClosed = _onClosed;
   }
 
@@ skipping 91 matching lines @@
   bool write(List<int> buffer, [bool copyBuffer = true]) {
     return _write(buffer, 0, buffer.length, copyBuffer);
   }
 
   bool writeFrom(List<int> buffer, [int offset = 0, int len]) {
     return _write(
         buffer, offset, (len == null) ? buffer.length - offset : len, true);
   }
 
   void close() {
+    if (_closing && _closed) return;
     if (!_pendingWrites.isEmpty()) {
       // Mark the socket for close when all data is written.
       _closing = true;
       _socket._onWrite = _onWrite;
     } else {
       // Close the socket for writing.
       _socket._closeWrite();
       _closed = true;
+      // Invoke the callback asynchronously.
+      new Timer(0, (t) {
+        if (_onClosed != null) _onClosed();
+      });
     }
   }
 
   void destroy() {
     _socket.onWrite = null;
     _pendingWrites.clear();
     _socket.close();
     _closed = true;
   }
 
   void set onNoPendingWrites(void callback()) {
     _onNoPendingWrites = callback;
     if (_onNoPendingWrites != null) {
       _socket._onWrite = _onWrite;
     }
   }
 
+  void set onClosed(void callback()) {
+    _onClosed = callback;
+  }
+
   bool _write(List<int> buffer, int offset, int len, bool copyBuffer) {
     if (_closing || _closed) throw new StreamException("Stream closed");
     int bytesWritten = 0;
     if (_pendingWrites.isEmpty()) {
       // If nothing is buffered write as much as possible and buffer
       // the rest.
       bytesWritten = _socket.writeList(buffer, offset, len);
       if (bytesWritten == len) return true;
     }
 
@@ skipping 22 matching lines @@
       if (bytesWritten < bytesToWrite) {
         _socket._onWrite = _onWrite;
         return;
       }
     }
 
     // All buffered data was written.
     if (_closing) {
       _socket._closeWrite();
       _closed = true;
+      if (_onClosed != null) {
+        _onClosed();
+      }
     } else {
       if (_onNoPendingWrites != null) _onNoPendingWrites();
     }
     if (_onNoPendingWrites == null) {
       _socket._onWrite = null;
     } else {
       _socket._onWrite = _onWrite;
     }
   }
 
   bool _onSocketError(e) {
     close();
     if (_onError != null) {
       _onError(e);
       return true;
     } else {
       return false;
     }
   }
 
   Socket _socket;
   _BufferList _pendingWrites;
   Function _onNoPendingWrites;
+  Function _onClosed;
   bool _closing = false;
   bool _closed = false;
 }