1.同步调用场景
1.1 背景
MQTT协定是基于PUB/SUB的异步通信模式，无奈实现服务端下发指令给设施端，同时须要设施端返回响应后果的场景。
IoT物联网平台基于MQTT协定制订了一套申请和响应的同步机制，无需改变MQTT协定即可实现同步通信。应用服务器通过POP API发动Rrpc调用，IoT设施端只须要在Timeout内，依照固定的格局回复Pub音讯，服务端即可同步获取IoT设施端的响应后果。
具体流程如下：
1.2 Topic格局约定
申请：/sys/${productKey}/${deviceName}/rrpc/request/${messageId}
响应：/sys/${productKey}/${deviceName}/rrpc/response/${messageId}
$示意变量，每个设施不同
messageId为IoT平台生成的音讯ID，设施端回复responseTopic里的messageId要与requestTopic统一
示例：
设施端须要订阅:
/sys/${productKey}/${deviceName}/rrpc/request/+
运行中设施收到Topic：
/sys/PK100101/DN213452/rrpc/request/443859344534
收到音讯后，在timeout工夫内回复Topic：
/sys/PK100101/DN213452/rrpc/response/443859344534
2.同步调用RRPC示例
2.1 设施端代码
const mqtt = require('aliyun-iot-mqtt');//设施属性const options = require("./iot-device-config.json");//建设连贯const client = mqtt.getAliyunIotMqttClient(options);client.subscribe(`/sys/${options.productKey}/${options.deviceName}/rrpc/request/+`)client.on('message', function(topic, message) { if(topic.indexOf(`/sys/${options.productKey}/${options.deviceName}/rrpc/request/`)>-1){ handleRrpc(topic, message) }})function handleRrpc(topic, message){ topic = topic.replace('/request/','/response/'); console.log("topic=" + topic) //一般Rrpc，响应payload自定义 const payloadJson = {code:200,msg:"handle ok"}; client.publish(topic, JSON.stringify(payloadJson));}2.2 服务端POP调用Rrpc
const co = require('co');const RPCClient = require('@alicloud/pop-core').RPCClient;const options = require("./iot-ak-config.json");//1.初始化clientconst client = new RPCClient({ accessKeyId: options.accessKey, secretAccessKey: options.accessKeySecret, endpoint: 'https://iot.cn-shanghai.aliyuncs.com', apiVersion: '2017-04-20'});const payload = { "msg": "hello Rrpc"};//2.构建requestconst params = { ProductKey:"a1gMu82K4m2", DeviceName:"h5@nuwr5r9hf6l@1532088166923", RequestBase64Byte:new Buffer(JSON.stringify(payload)).toString("base64"), Timeout:3000};co(function*() { //3.发动API调用 const response = yield client.request('Rrpc', params); console.log(JSON.stringify(response));});rrpc响应：
{ "MessageId": "1037292594536681472", "RequestId": "D2150496-2A61-4499-8B2A-4B3EC4B2A432", "PayloadBase64Byte": "eyJjb2RlIjoyMDAsIm1zZyI6ImhhbmRsZSBvayJ9", "Success": true, "RrpcCode": "SUCCESS"}// PayloadBase64Byte 解码: {"code":200,"msg":"handle ok"}3.物模型-服务同步调用InvokeThingService示例
留神：物模型 服务调用 接口InvokeThingService，不是Rrpc
3.1 物模型-同步服务定义
3.2 设施端实现
const mqtt = require('aliyun-iot-mqtt');//设施属性const options = require("./iot-device-config.json");//建设连贯const client = mqtt.getAliyunIotMqttClient(options);client.subscribe(`/sys/${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，须要通过payload里的method辨别*/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构造： const payloadJson = { id: Date.now(), code:200, data: { currentMode: Math.floor((Math.random() * 20) + 10) } } client.publish(topic, JSON.stringify(payloadJson));}留神：设施端响应的payload要满足物模型定义的出参构造
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clientconst 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.发动API调用 const response = yield client.request('InvokeThingService', params); console.log(JSON.stringify(response)); } catch (err) { console.log(err); }});调用后果：
{ "Data":{ "Result": "{\"currentMode\":12}", "MessageId": "1536145625658" }, "RequestId": "29FD78CE-D1FF-48F7-B0A7-BD52C142DD7F", "Success": true}物联网平台产品介绍详情：https://www.aliyun.com/product/iot/iot_instc_public_cn
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