# 3.12 PINGREQ – 心跳请求

客户端发送PINGREQ报文给服务端的。用于：

1. 在没有任何其它控制报文从客户端发给服务的时，告知服务端客户端还活着。
2. 请求服务端发送 响应确认它还活着。
3. 使用网络以确认网络连接没有断开。

保持连接（Keep Alive）处理中用到这个报文，详细信息请查看 3.1.2.10节。

## 3.12.1 固定报头

#### 图例 3.33 – PINGREQ报文固定报头

| **Bit** |      **7**      | **6** | **5** | **4** | **3** | **2** | **1** | **0** |
| :-----: | :-------------: | :---: | :---: | :---: | :---: | :---: | :---: | :---: |
|  byte 1 | MQTT控制报文类型 (12) |  保留位  |       |       |       |       |       |       |
|         |        1        |   1   |   0   |   0   |   0   |   0   |   0   |   0   |
|  byte 2 |     剩余长度 (0)    |       |       |       |       |       |       |       |
|         |        0        |   0   |   0   |   0   |   0   |   0   |   0   |   0   |

## 3.12.2 可变报头

PINGREQ报文没有可变报头。

## 3.12.3 有效载荷

PINGREQ报文没有有效载荷。

## 3.12.4 响应

服务端**必须**发送 PINGRESP报文响应客户端的PINGREQ报文 \[MQTT-3.12.4-1]。

## 第三章目录 MQTT控制报文

* [3.0 Contents – MQTT控制报文](/mqtt/03-controlpackets.md)
* [3.1 CONNECT – 连接服务端](/mqtt/03-controlpackets/0301-connect.md)
* [3.2 CONNACK – 确认连接请求](/mqtt/03-controlpackets/0302-connack.md)
* [3.3 PUBLISH – 发布消息](/mqtt/03-controlpackets/0303-publish.md)
* [3.4 PUBACK –发布确认](/mqtt/03-controlpackets/0304-puback.md)
* [3.5 PUBREC – 发布收到（QoS 2，第一步）](/mqtt/03-controlpackets/0305-pubrec.md)
* [3.6 PUBREL – 发布释放（QoS 2，第二步）](/mqtt/03-controlpackets/0306-pubrel.md)
* [3.7 PUBCOMP – 发布完成（QoS 2，第三步）](/mqtt/03-controlpackets/0307-pubcomp.md)
* [3.8 SUBSCRIBE - 订阅主题](/mqtt/03-controlpackets/0308-subscribe.md)
* [3.9 SUBACK – 订阅确认](/mqtt/03-controlpackets/0309-suback.md)
* [3.10 UNSUBSCRIBE –取消订阅](/mqtt/03-controlpackets/0310-unsubscribe.md)
* [3.11 UNSUBACK – 取消订阅确认](/mqtt/03-controlpackets/0311-unsuback.md)
* [3.12 PINGREQ – 心跳请求](/mqtt/03-controlpackets/0312-pingreq.md)
* [3.13 PINGRESP – 心跳响应](/mqtt/03-controlpackets/0313-pingresp.md)
* [3.14 DISCONNECT –断开连接](/mqtt/03-controlpackets/0314-disconnect.md)

## 项目主页

* [MQTT协议中文版](https://github.com/mcxiaoke/mqtt)


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