@Override
    public void pingResp(final ChannelHandlerContext ctx) {
        MqttFixedHeader pingreqFixedHeader = new MqttFixedHeader(MqttMessageType.PINGRESP, false,
                MqttQoS.AT_MOST_ONCE, false, 0);
        MqttMessage pingResp = new MqttMessage(pingreqFixedHeader);
        ctx.writeAndFlush(pingResp);
    }
Mqtt Server send pingresp to respond to pingreq of the client.
shenyu-protocol/shenyu-protocol-mqtt/src/main/java/org/apache/shenyu/protocol/mqtt/PingResp.java