Mqtt（emqx）上下线监听

其他 2020-04-11 11:38:31 阅读次数: 0

在mqtt协议中，存在LTW（Last Will and Testament）遗言机制，该机制只能捕捉客户端异常离线的通知，而无法获取正常通过disconnect断开连接的通知。

LTW（Last Will and Testament）遗言机制
客户端在连接到Mqtt服务器时，需指定will topic和will message遗言信息，
之后若在客户端异常断开（弱网络、服务被终止，而非正常disconnet）时会由mqtt服务器主动向will topic发送will message，
此时其他监听will topic的用户即可获得客户端离线的will遗言通知；

而在Emqx，存在系统主题订阅，其中的系统主题$SYS/brokers/${node}/clients/${clientId}/connected, $SYS/brokers/${node}/clients/${clientId}/disconnected同样支持客户端上线、下线的通知；

LWT和Emqx SYS主题通知效果对比

机制＼事件 connect disconnect 异常disconnect
$SYS/brokers/${node}/clients/${clientId}/connected ✔
$SYS/brokers/${node}/clients/${clientId}/disconnected ✔ ✔
LWT ✔

通过实际测试对比发现，LWT仅支持异常disconnect的通知，而emqx的$SYS/brokers/${node}/clients/${clientId}/disconnected系统主题可以捕捉到所有离线通知（主动diconnect、异常disconnect），即emqx的系统主题即可完整支持客户端上线、下线监听的需求。可以根据实际的需求选择适当的机制。
若使用LWT机制、结合retained messages亦可以实现客户端上线、下线的监听，LWT上下线监听参考方案如下：

client1在connect时指定lastWillMessage “Offline”，同时设置lastWillRetain为true, lastWillTopic设置为client1/status，
client1在连接成功（包括之后每次重连成功）时主动publish消息"Online"（且消息retained设置为true）到同一主题client1/status，
client1在主动disconnect之前，都要主动publish消息"Offline"（且消息retained设置为true）到同一主题client1/status，
client1在异常disconnect时，mqtt服务器都会主动publish消息"Offline"（且消息retained设置为true）到同一主题client1/status，
如此，只要client1在线时，client1/status中的消息都是Online, 而只要client1离线时，client1/status中的消息都是offline，
而使用retained消息（保留最新的一条消息）即可保证其他订阅该主题的客户端总能获得client1的最新在线状态，
该方式每个客户端指定唯一will topic如clientId/status，而关注用户上下线的客户端可以统一订阅主题+/status以获得其他所有客户端的上下线状态。
参考链接：MQTT Essentials: Part 9 last-will-and-testament

若mqtt服务器为emqx，推荐使用SYS主题方式。

emqx设置

在这里插入图片描述
参考官网：用户指南->$SYS-系统主题

（1）修改etc/acl.conf
设置allow所有用户订阅$SYS/brokers/+/clients/#主题

{allow, {user, "dashboard"}, subscribe, ["$SYS/#"]}.

{allow, {ipaddr, "127.0.0.1"}, pubsub, ["$SYS/#", "#"]}.

{allow, all, subscribe, ["$SYS/brokers/+/clients/#"]}.

{deny, all, subscribe, ["$SYS/#", {eq, "#"}]}.

{allow, all}.

参看官网：配置说明->匿名认证与 ACL 文件

（2）重新加载acl文件（或者重启emqx服务）

$ ./bin/emqx_ctl acl reload

参看官网：管理命令->acl命令

示例代码

示例代码均采用hivemq客户端、mqtt5

客户端代码

package com.mx.mqtt.sys;

import com.hivemq.client.mqtt.datatypes.MqttQos;
import com.hivemq.client.mqtt.lifecycle.MqttClientConnectedContext;
import com.hivemq.client.mqtt.lifecycle.MqttClientConnectedListener;
import com.hivemq.client.mqtt.lifecycle.MqttClientDisconnectedContext;
import com.hivemq.client.mqtt.lifecycle.MqttClientDisconnectedListener;
import com.hivemq.client.mqtt.mqtt5.Mqtt5AsyncClient;
import com.hivemq.client.mqtt.mqtt5.Mqtt5BlockingClient;
import com.hivemq.client.mqtt.mqtt5.Mqtt5Client;
import com.hivemq.client.mqtt.mqtt5.exceptions.Mqtt5ConnAckException;
import com.hivemq.client.mqtt.mqtt5.message.auth.Mqtt5SimpleAuth;
import com.hivemq.client.mqtt.mqtt5.message.connect.connack.Mqtt5ConnAck;
import com.mx.mqtt.config.Consts;
import com.mx.mqtt.jwt.JwtUtils;
import com.mx.mqtt.utils.CommonUtils;

/**
 * emqx - 客户端（指定LWT配置）
 *
 * @Ahthor luohq
 * @Date 2020-04-09
 */
public class EmqxClient {

    private static final String SYS_TOPIC_CONNECTED = "$SYS/brokers/+/clients/+/connected";
    private static final String SYS_TOPIC_DISCONNECTED = "$SYS/brokers/+/clients/+/disconnected";

    private static final String MQTT_JWT_SECRET = "xxxx";
    private static final String MQTT_SERVER_HOST = "192.168.xx.xxx";
    private static final Integer MQTT_SERVER_PORT = 1883;
    private static final String MQTT_CLIENT_ID = "luohq" + CommonUtils.uuid();
    private static final String MQTT_LWT_TOPIC = "lwt";


    public static void main(String[] args) {
        Mqtt5BlockingClient client = buildMqtt5Client();
        Mqtt5AsyncClient asyncClient = client.toAsync();
    }


    public static Mqtt5BlockingClient buildMqtt5Client() {
        /** blocking客户端 */
        Mqtt5BlockingClient client = Mqtt5Client.builder()
                .identifier(MQTT_CLIENT_ID)
                .serverHost(MQTT_SERVER_HOST)
                .serverPort(MQTT_SERVER_PORT)
                .addConnectedListener(new MqttClientConnectedListener() {
                    @Override
                    public void onConnected(MqttClientConnectedContext context) {
                        System.out.println("mqtt onConnected context");
                    }
                })
                .addDisconnectedListener(new MqttClientDisconnectedListener() {
                    @Override
                    public void onDisconnected(MqttClientDisconnectedContext context) {
                        System.out.println("mqtt onDisconnected context");
                    }
                })
                //自动重连（指数级延迟重连（起始延迟1s，之后每次2倍，到2分钟封顶） delay : 1s-> 2s -> 4s -> ... -> 2min）
                .automaticReconnectWithDefaultConfig()
                /** 指定LWT */
                .willPublish()
                    .topic(MQTT_LWT_TOPIC)
                    .qos(MqttQos.EXACTLY_ONCE)
                    //will内容：clientId
                    .payload(MQTT_CLIENT_ID.getBytes())
                    .applyWillPublish()
                .buildBlocking();
        /** Emqx JWT认证 */
        String authJwt = JwtUtils.generateJwt(MQTT_CLIENT_ID, MQTT_JWT_SECRET);
        Mqtt5SimpleAuth auth = Mqtt5SimpleAuth.builder()
                .username(MQTT_CLIENT_ID)
                .password(authJwt.getBytes())
                .build();
        Mqtt5ConnAck connAck = null;
        try {
            connAck = client.connectWith()
                    .simpleAuth(auth)
                    /** cleanSession=false */
                    .cleanStart(false)
                    /** session 7天过期 */
                    .sessionExpiryInterval(Consts.MqttConsts.SESSION_EXPIRATION)
                    /** keepalive 时长*/
                    .keepAlive(60)
                    .send();
        } catch (Mqtt5ConnAckException e) {
            e.printStackTrace();
            connAck = e.getMqttMessage();
        }


        /** 连接(普通无密码连接) */
        //Mqtt5ConnAck connAck = client.connect();

        System.out.println(connAck.getReasonCode() + ":" + connAck.getReasonString() + ":" + connAck.getResponseInformation());
        if (connAck.getReasonCode().isError()) {
            System.err.println("Mqtt5连接失败！");
            System.exit(-1);
        }
        return client;
    }
}

监听端代码

package com.mx.mqtt.sys;

import com.hivemq.client.mqtt.datatypes.MqttQos;
import com.hivemq.client.mqtt.lifecycle.MqttClientConnectedContext;
import com.hivemq.client.mqtt.lifecycle.MqttClientConnectedListener;
import com.hivemq.client.mqtt.lifecycle.MqttClientDisconnectedContext;
import com.hivemq.client.mqtt.lifecycle.MqttClientDisconnectedListener;
import com.hivemq.client.mqtt.mqtt5.Mqtt5AsyncClient;
import com.hivemq.client.mqtt.mqtt5.Mqtt5BlockingClient;
import com.hivemq.client.mqtt.mqtt5.Mqtt5Client;
import com.hivemq.client.mqtt.mqtt5.exceptions.Mqtt5ConnAckException;
import com.hivemq.client.mqtt.mqtt5.message.auth.Mqtt5SimpleAuth;
import com.hivemq.client.mqtt.mqtt5.message.connect.connack.Mqtt5ConnAck;
import com.hivemq.client.mqtt.mqtt5.message.publish.Mqtt5Publish;
import com.mx.mqtt.config.Consts;
import com.mx.mqtt.jwt.JwtUtils;
import com.mx.mqtt.utils.CommonUtils;
import org.apache.logging.log4j.LogManager;
import org.apache.logging.log4j.Logger;

import java.io.UnsupportedEncodingException;

/**
 * emqx - SYS - 主题监控
 *
 * @Ahthor luohq
 * @Date 2020-04-09
 */
public class EmqxSysListener {

    /**
     * 日志
     */
    private static final Logger logger = LogManager.getLogger(EmqxSysListener.class);

    private static final String SYS_TOPIC_CONNECTED = "$SYS/brokers/+/clients/+/connected";
    private static final String SYS_TOPIC_DISCONNECTED = "$SYS/brokers/+/clients/+/disconnected";

    private static final String MQTT_JWT_SECRET = "xxxx";
    private static final String MQTT_SERVER_HOST = "192.168.xx.xxx";
    private static final Integer MQTT_SERVER_PORT = 1883;
    private static final String MQTT_CLIENT_ID = "luohq";
    private static final String MQTT_LWT_TOPIC = "lwt";


    public static void main(String[] args) {
        Mqtt5BlockingClient client = buildMqtt5Client();
        Mqtt5AsyncClient asyncClient = client.toAsync();

        //订阅主题
        asyncClient.subscribeWith()
                .topicFilter(SYS_TOPIC_CONNECTED)
                .qos(MqttQos.EXACTLY_ONCE)
                //消费主题消息（异步）
                .callback(mqtt5Publish -> {
                    printMsg("CONNECTED", mqtt5Publish);
                })
                .send();

        //订阅主题
        asyncClient.subscribeWith()
                .topicFilter(SYS_TOPIC_DISCONNECTED)
                .qos(MqttQos.EXACTLY_ONCE)
                //消费主题消息（异步）
                .callback(mqtt5Publish -> {
                    printMsg("DISCONNECTED", mqtt5Publish);
                })
                .send();

        //订阅主题
        asyncClient.subscribeWith()
                .topicFilter(MQTT_LWT_TOPIC)
                .qos(MqttQos.EXACTLY_ONCE)
                //消费主题消息（异步）
                .callback(mqtt5Publish -> {
                    printMsg("LWT", mqtt5Publish);
                })
                .send();

    }


    public static Mqtt5BlockingClient buildMqtt5Client() {
        /** blocking客户端 */
        Mqtt5BlockingClient client = Mqtt5Client.builder()
                .identifier(MQTT_CLIENT_ID)
                .serverHost(MQTT_SERVER_HOST)
                .serverPort(MQTT_SERVER_PORT)
                .addConnectedListener(new MqttClientConnectedListener() {
                    @Override
                    public void onConnected(MqttClientConnectedContext context) {
                        System.out.println("mqtt onConnected context");
                    }
                })
                .addDisconnectedListener(new MqttClientDisconnectedListener() {
                    @Override
                    public void onDisconnected(MqttClientDisconnectedContext context) {
                        System.out.println("mqtt onDisconnected context");
                    }
                })
                //自动重连（指数级延迟重连（起始延迟1s，之后每次2倍，到2分钟封顶） delay : 1s-> 2s -> 4s -> ... -> 2min）
                .automaticReconnectWithDefaultConfig()
                .buildBlocking();
        /** Emqx JWT认证 */
        String authJwt = JwtUtils.generateJwt(MQTT_CLIENT_ID, MQTT_JWT_SECRET);
        Mqtt5SimpleAuth auth = Mqtt5SimpleAuth.builder()
                .username(MQTT_CLIENT_ID)
                .password(authJwt.getBytes())
                .build();
        Mqtt5ConnAck connAck = null;
        try {
            connAck = client.connectWith()
                    .simpleAuth(auth)
                    /** cleanSession=false */
                    .cleanStart(false)
                    /** session 7天过期 */
                    .sessionExpiryInterval(Consts.MqttConsts.SESSION_EXPIRATION)
                    .send();
        } catch (Mqtt5ConnAckException e) {
            e.printStackTrace();
            connAck = e.getMqttMessage();
        }


        /** 连接(普通无密码连接) */
        //Mqtt5ConnAck connAck = client.connect();

        System.out.println(connAck.getReasonCode() + ":" + connAck.getReasonString() + ":" + connAck.getResponseInformation());
        if (connAck.getReasonCode().isError()) {
            logger.error("Mqtt5连接失败！");
            System.exit(-1);
        }
        return client;
    }

    private static void printMsg(String label, Mqtt5Publish mqtt5Publish) {
        try {
            String msgStr = new String(mqtt5Publish.getPayloadAsBytes(), "UTF-8");
            logger.info(CommonUtils.buildStr("【", label, "】", msgStr));
        } catch (UnsupportedEncodingException e) {
            e.printStackTrace();
        }
    }
}
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