Node JS 如何使用 MQTT 协议调用“直接方法”

Azure IOT SDK 中封装了使用 MQTT 协议调用“直接方法”的用法，如果想直接使用 MQTT 协议自己调用 Azure IOT 来实现“直接方法”的调用，虽然官方文档也有介绍，但依照官方文档的步骤，依然无法调用，这是因为文档中讲解到的一些参数并不详细，具体可以参考以下文档和代码 :

使用 NodeJS 调用 MQTT 协议，需要依赖 MQTT.JS。

首先建立 NodeJS 项目目录，然后安装 MQTT 依赖包 :

npm install mqtt --save

其次，在代码中配置连接 IOT 字符串，连接并接受云端通过调用“直接方法”发送来的消息 :

var mqtt = require('mqtt')
var URL = require('url');
var QueryString = require('querystring');

var options = {
    cmd: 'connect',
    protocolId: 'MQTT',
    protocolVersion: 4,
    clean: false,
    clientId: 'kevindevice',
    rejectUnauthorized: true,
    username: 'xuhuaIOT.azure-devices.cn/kevindevice/api-version=2016-11-14',
    reconnectPeriod: 0, // Client will handle reconnection at the higher level
    password : new Buffer('SharedAccessSignature sr=xuhuaIOT.azure-devices.cn%2Fdevices%2Fkevindevice&sig=wU3c8uu6AqTKoKF0OAtBE3K7ZcAkhelhFux6vNYEiho%3D&se=1485411010')
};
var client = mqtt.connect('mqtts://xuhuaIOT.azure-devices.cn', options);

client.on('connect', () => {
    client.subscribe('$iothub/methods/POST/#', { qos: 0 }, function (err) {
        if (err) {
            console.error("Direct method error: " + err.message);
        } else {
            console.log("Successfully subscribe to direct method");
        }
    });

})

client.on('message', (topic, message) => {
    console.log(topic);
    var methodMessage = parseMessage(topic, message);
    console.log('message' + methodMessage);

    client.publish('$iothub/methods/res/200/?$rid=' + methodMessage.requestId, JSON.stringify({"message":"reboot successfully"}), { qos: 0, retain: false }, function(err) {});
})

var handleRebootRequest = function(message) {
    console.log('Response to method \'' + message + '\' sent successfully.');
}

var parseMessage = function(topic, body) {
var url, path, query;
try {
    url = URL.parse(topic);
    path = url.path.split('/');
    query = QueryString.parse(url.query);
}
catch(err) {
    console.error(err)
    return undefined;
}

// if the topic has a querystring then 'path' will include it; so
// we strip it out
var lastPathComponent = path[path.length - 1];
if(lastPathComponent.indexOf('?') !== -1) {
    path[path.length - 1] = lastPathComponent.substr(
    0, lastPathComponent.indexOf('?')
    );
}

if(path.length > 0 && path[0] === '$iothub') {
    var message = {};
    if(path.length > 1 && path[1].length > 0) {
    // create an object for the module; for example, $iothub/twin/...
    // would result in there being a message.twin object
    var mod = message[path[1]] = {};

    // parse the request ID if there is one
    if(!!(query.$rid)) {
        message.requestId = query.$rid;
    }

    // parse the other properties properties (excluding $rid)
    message.properties = query;
    delete message.properties.$rid;

    // save the body
    message.body = body;

    // parse the verb
    if(path.length > 2 && path[2].length > 0) {
        mod.verb = path[2];

        // This is a topic that looks like this:
        //  $iothub/methods/POST/{method name}?$rid={request id}&{serialized properties}
        // We parse the method name out.
        if(path.length > 3 && path[3].length > 0) {
        mod.methodName = path[3];
        } else {
        // The service published a message on a strange topic name. This is
        // probably a service bug. At any rate we don't know what to do with
        // this strange topic so we throw.
        throw new Error('Device method call\'s MQTT topic name does not include the method name.');
        }
    }
    }
    return message;
}
return undefined;
}

本示例是设备接受 Azure IOTHub 云端调用“直接方法”发来的消息，并进行响应处理。

参考文档：

Azure IoT 中心使用直接方法
Azure IoT 中心直接方法的介绍