如何在 Netty 4 中处理 PING/PONG 帧？答案

【问题标题】：How to handle PING/PONG frame in Netty 4?如何在 Netty 4 中处理 PING/PONG 帧？
【发布时间】：2019-01-07 01:42:36
【问题描述】：

class ClientWebSocketHandler extends SimpleChannelInboundHandler<WebSocketFrame> {

  @Override
    protected void channelRead0(ChannelHandlerContext ctx, WebSocketFrame frame) throws Exception {

    }
}

我只能在channelRead0 中接收TextWebSocketFrame 和BinaryWebSocketFrame

PingWebSocketFrame和PongWebSocketFrame怎么处理，我想知道客户端什么时候发Ping/Pong

【问题讨论】：

标签： netty

【解决方案1】：

像这样：（知道当时 channelRead0 已被弃用，应该在 5.0 版本之后被删除或不支持，如果您想要最新的答案，请在评论中询问）

/**
 * * <strong>Please keep in mind that this method will be renamed to
 * {@code messageReceived(ChannelHandlerContext, I)} in 5.0.</strong>
 */
@Override
public void channelRead0(ChannelHandlerContext ctx, Object msg) throws Exception {
    Channel ch = ctx.channel();
    if (!handshaker.isHandshakeComplete()) {
        handshaker.finishHandshake(ch, (FullHttpResponse) msg);
        l.error("WebSocket Client connected!");
        handshakeFuture.setSuccess();
        return;
    }

    if (msg instanceof FullHttpResponse) {
        FullHttpResponse response = (FullHttpResponse) msg;
        throw new IllegalStateException("Unexpected FullHttpResponse (getStatus=" + response.status() + ", content="
            + response.content().toString(CharsetUtil.UTF_8) + ')');
    }


    WebSocketFrame frame = (WebSocketFrame) msg;
    if (frame instanceof TextWebSocketFrame) {
        TextWebSocketFrame textFrame = (TextWebSocketFrame) frame;
        l.info("WebSocket Client received message:{} ", textFrame.text());

        //needed if the server close the socket if no ping send for long
        //better to send the ping with a timer
        // it allwos to choose the rate
        ch.write(new PingWebSocketFrame());

    } else if (frame instanceof PongWebSocketFrame) {
        l.info("WebSocket Client received pong");
    } else if (frame instanceof CloseWebSocketFrame) {
        l.info("WebSocket Client received closing");
        ch.close();
    }
}

【讨论】：

如何用定时器发送 ping？
尝试将您的 channel.write 包含在这样的计时器中：``` public void channelConnected(ChannelHandlerContext ctx, ChannelStateEvent e) throws Exception { ... this.timerLocal.newTimeout(new TimerTask() { public void run(Timeout timeout) throws Exception { Channel ch = ctx.getChannel(); ch.write("data data data"); } }, 25, TimeUnit.SECONDS); ... } ``` stackoverflow.com/questions/8934449/…

【解决方案2】：

在任何 WebSocketFrame 到达您的 SimpleChannelInboundHandler 之前，Netty 已经接收到 PingWebSocketFrame 和 PongWebSocketFrame。有关其处理逻辑，请参阅摘要 WebSocketProtocolHandler。

【讨论】：