基于Pub/Sub模式的同步调用实战

1.同步调用场景

1.1 背景

MQTT协议是基于PUB/SUB的异步通信模式，无法实现服务端下发指令给设备端，同时需要设备端返回响应结果的场景。
IoT物联网平台基于MQTT协议制定了一套请求和响应的同步机制，无需改动MQTT协议即可实现同步通信。应用服务器通过POP API发起Rrpc调用，IoT设备端只需要在Timeout内，按照固定的格式回复Pub消息，服务端即可同步获取IoT设备端的响应结果。

具体流程如下：

1.2 Topic格式约定

请求：/sys/${productKey}/${deviceName}/rrpc/request/${messageId}**<br />**响应：**/sys/${productKey}/${deviceName}/rrpc/**response**/**${messageId}

$表示变量，每个设备不同
messageId为IoT平台生成的消息ID，
设备端回复responseTopic里的messageId要与requestTopic一致

示例：

设备端需要订阅:

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

运行中设备收到Topic：

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

收到消息后，在timeout时间内回复Topic：

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

2.同步调用RRPC示例

2.1 设备端代码

const mqtt = require('aliyun-iot-mqtt');
//设备属性
const options = require("./iot-device-config.json");
//建立连接
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，响应payload自定义
    const payloadJson = {code:200,msg:"handle ok"};
    client.publish(topic, JSON.stringify(payloadJson));
}

2.2 服务端POP调用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.构建request
const params = {
    ProductKey:"a1gMu82K4m2",
    DeviceName:"h5@nuwr5r9hf6l@1532088166923",
    RequestBase64Byte:new Buffer(JSON.stringify(payload)).toString("base64"),
    Timeout:3000
};

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

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

rrpc响应：

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

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

3.物模型-服务同步调用InvokeThingService示例

注意：物模型 服务调用 接口InvokeThingService，不是Rrpc

设备订阅subTopic

注意：服务同步调用API是InvokeThingService

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

IoT云端下行的payload格式

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

设备响应replyTopic

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

设备响应payload格式

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

3.1 物模型-同步服务定义

3.2 设备端实现

const mqtt = require('aliyun-iot-mqtt');
//设备属性
const options = require("./iot-device-config.json");
//建立连接
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)
    }
})
/*
* 如果存在多个同步调用服务，需要通过payload里的method区分
*/
function handleRrpc(topic, message){

    topic = topic.replace('/request/','/response/');
    console.log("topic=" + topic)
    //物模型 同步服务调用，响应payload结构：
    const payloadJson = {
        id: Date.now(),
        code:200,
        data: {
            currentMode: Math.floor((Math.random() * 20) + 10)
        }
    }

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

注意：设备端响应的payload要满足物模型定义的出参结构

3.3 服务端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.发起API调用
        const response = yield client.request('InvokeThingService', params);

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

调用结果：

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