Add ability to send a ping interval on a WebSocket.

sdk/lib/io/websocket.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;
 
 /**
  * Web socket status codes used when closing a web socket connection.
  */
 abstract class WebSocketStatus {
@@ skipping 113 matching lines @@
    */
   int get closeCode;
 
   /**
    * The close reason set when the web socket connection is closed. If
    * there is no close reason available this property will be [:null:]
    */
   String get closeReason;
 
   /**
+   * Set and get the interval for sending ping signals. If a ping message is not
+   * answered by a pong message from the peer, the `WebSocket` is assumed
+   * disconnected and the connection is closed with a
+   * [WebSocketStatus.GOING_AWAY] close code. When a ping signal is sent, the
+   * pong message must be received within [pingInterval].
+   *
+   * There are never two outstanding pings at any given time, and the next ping
+   * timer starts when the pong is received.
+   *
+   * Set the [pingInterval] to `null` to disable sending ping messages.
+   *
+   * The default value is `null`.
+   */
+  Duration pingInterval;
+
+  /**
    * Closes the web socket connection. Set the optional [code] and [reason]
    * arguments to send close information to the remote peer. If they are
    * omitted, the peer will see [WebSocketStatus.NO_STATUS_RECEIVED] code
    * with no reason.
    */
   Future close([int code, String reason]);
 
   /**
    * Sends data on the web socket connection. The data in [data] must
    * be either a [:String:], or a [:List<int>:] holding bytes.
    */
   void add(data);
 
   /**
    * Sends data from a stream on web socket connection. Each data event from
    * [stream] will be send as a single WebSocket frame. The data from [stream]
    * must be either [:String:]s, or [:List<int>:]s holding bytes.
    */
   Future addStream(Stream stream);
 }
 
 
 class WebSocketException implements IOException {
   const WebSocketException([String this.message = ""]);
   String toString() => "WebSocketException: $message";
   final String message;
 }