基於Pub/Sub模式的同步調用實戰

1.同步調用場景

1.1 背景

MQTT協議是基於PUB/SUB的異步通信模式，無法實現服務端下發指令給設備端，同時需要設備端返回響應結果的場景。
IoT物聯網平臺基於MQTT協議制定了一套請求和響應的同步機制，無需改動MQTT協議即可實現同步通信。應用服務器通過POP API發起Rrpc調用，IoT設備端只需要在Timeout內，按照固定的格式回覆Pub消息，服務端即可同步獲取IoT設備端的響應結果。

具體流程如下：

1.2 Topic格式約定

請求：/sys/${productKey}/${deviceName}/rrpc/request/${messageId}
響應：/sys/${productKey}/${deviceName}/rrpc/**response**/**${messageId}**

$表示變量，每個設備不同
messageId為IoT平臺生成的消息ID，
設備端回覆responseTopic裡的messageId要與requestTopic一致

示例：

設備端需要訂閱:

/sys/${productKey}/${deviceName}/rrpc/request/+

運行中設備收到Topic：

/sys/PK100101/DN213452/rrpc/request/443859344534

收到消息後，在timeout時間內回覆Topic：

/sys/PK100101/DN213452/rrpc/response/443859344534

2.同步調用RRPC示例

2.1 設備端代碼

const mqtt = require('aliyun-iot-mqtt');
//設備屬性
const options = require("./iot-device-config.json");
//建立連接
const client = mqtt.getAliyunIotMqttClient(options);

client.subscribe(`/sys/${options.productKey}/${options.deviceName}/rrpc/request/+`)
client.on('message', function(topic, message) {
    
    if(topic.indexOf(`/sys/${options.productKey}/${options.deviceName}/rrpc/request/`)>-1){
        handleRrpc(topic, message)
    }
})

function handleRrpc(topic, message){
    topic = topic.replace('/request/','/response/');
    console.log("topic=" + topic)
    //普通Rrpc，響應payload自定義
    const payloadJson = {code:200,msg:"handle ok"};
    client.publish(topic, JSON.stringify(payloadJson));
}

2.2 服務端POP調用Rrpc

const co = require('co');
const RPCClient = require('@alicloud/pop-core').RPCClient;

const options = require("./iot-ak-config.json");

//1.初始化client
const client = new RPCClient({
    accessKeyId: options.accessKey,
    secretAccessKey: options.accessKeySecret,
    endpoint: 'https://iot.cn-shanghai.aliyuncs.com',
    apiVersion: '2018-01-20'
});

const payload = {
  "msg": "hello Rrpc"
};

//2.構建request
const params = {
    ProductKey:"a1gMu82K4m2",
    DeviceName:"h5@nuwr5r9hf6l@1532088166923",
    RequestBase64Byte:new Buffer(JSON.stringify(payload)).toString("base64"),
    Timeout:3000
};

co(function*() {
    //3.發起API調用
    const response = yield client.request('Rrpc', params);

    console.log(JSON.stringify(response));
});

rrpc響應：

{
    "MessageId": "1037292594536681472",
    "RequestId": "D2150496-2A61-4499-8B2A-4B3EC4B2A432",
    "PayloadBase64Byte": "eyJjb2RlIjoyMDAsIm1zZyI6ImhhbmRsZSBvayJ9",
    "Success": true,
    "RrpcCode": "SUCCESS"
}

// PayloadBase64Byte 解碼: {"code":200,"msg":"handle ok"}

3.物模型-服務同步調用InvokeThingService示例

注意：物模型服務調用接口InvokeThingService，不是Rrpc

設備訂閱subTopic

注意：服務同步調用API是InvokeThingService

/sys/${productKey}/${deviceName}/rrpc/request/+

IoT雲端下行的payload格式

{
"id": 3536123,
"version": "1.0",
"params": {
"入參key1": "入參value1",
"入參key2": "入參value2"
},
"method": "thing.service.{tsl.service.identifier}"
}

設備響應replyTopic

/sys/${productKey}/${deviceName}/rrpc/response/request的消息Id

設備響應payload格式

{
"id": 3536123,
"code": 200,
"data": {
"出參key1": "出參value1",
"出參key2": "出參value2"
}
}

3.1 物模型-同步服務定義

3.2 設備端實現

const mqtt = require('aliyun-iot-mqtt');
//設備屬性
const options = require("./iot-device-config.json");
//建立連接
const client = mqtt.getAliyunIotMqttClient(options);

client.subscribe(`/sys/${options.productKey}/${options.deviceName}/rrpc/request/+`)
client.on('message', function(topic, message) {
    
    if(topic.indexOf(`/sys/${options.productKey}/${options.deviceName}/rrpc/request/`)>-1){
        handleRrpc(topic, message)
    }
})
/*
* 如果存在多個同步調用服務，需要通過payload裡的method區分
*/
function handleRrpc(topic, message){

    topic = topic.replace('/request/','/response/');
    console.log("topic=" + topic)
    //物模型 同步服務調用，響應payload結構：
    const payloadJson = {
        id: Date.now(),
        code:200,
        data: {
            currentMode: Math.floor((Math.random() * 20) + 10)
        }
    }

    client.publish(topic, JSON.stringify(payloadJson));
}

注意：設備端響應的payload要滿足物模型定義的出參結構

3.3 服務端POP 接口InvokeThingService

const co = require('co');
const RPCClient = require('@alicloud/pop-core').RPCClient;

const options = require("./iot-ak-config.json");

//1.初始化client
const client = new RPCClient({
    accessKeyId: options.accessKey,
    secretAccessKey: options.accessKeySecret,
    endpoint: 'https://iot.cn-shanghai.aliyuncs.com',
    apiVersion: '2018-01-20'
});

const params = {
    ProductKey: "a1gMu82K4m2",
    DeviceName: "h5@nuwr5r9hf6l@1532088166923",
    Args: JSON.stringify({ "mode": "1" }),
    Identifier: "thing.service.setMode"
};

co(function*() {
    try {
        //3.發起API調用
        const response = yield client.request('InvokeThingService', params);

        console.log(JSON.stringify(response));
    } catch (err) {
        console.log(err);
    }
});

調用結果：

{
    "Data":{
        "Result": "{\"currentMode\":12}",
        "MessageId": "1536145625658"
    },
    "RequestId": "29FD78CE-D1FF-48F7-B0A7-BD52C142DD7F",
    "Success": true
}

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