Fix WebSocket header construction for large frames.

runtime/bin/websocket_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 _WebSocketMessageType {
   static final int NONE = 0;
   static final int BINARY = 1;
   static final int TEXT = 2;
   static final int CLOSE = 3;
 }
@@ skipping 481 matching lines @@
     if (_onError != null) _onError(e);
     _socket.close();
   }
 
   _sendFrame(int opcode, List<int> data) {
     bool mask = false;  // Masking not implemented for server.
     int dataLength = data == null ? 0 : data.length;
     // Determine the header size.
     int headerSize = (mask) ? 6 : 2;
     if (dataLength > 65535) {
-      headerSize += 4;
+      headerSize += 8;
     } else if (dataLength > 126) {
       headerSize += 2;
     }
     List<int> header = new List<int>(headerSize);
     int index = 0;
     // Set FIN and opcode.
     header[index++] = 0x80 | opcode;
     // Determine size and position of length field.
     int lengthBytes = 1;
     int firstLengthByte = 1;
@@ skipping 77 matching lines @@
     }
     String key = request.headers.value("Sec-WebSocket-Key");
     if (key == null) {
       return false;
     }
     return true;
   }
 
   Function _onOpen;
 }