node.js下进行mqtt实践 | 看看俺 – KanKanAn.com

通过 mqtt 可以将设备连接在一起，能够实现将消息（可能来自服务器也可能来自其它设备）推送到设备，如果设备离线， 服务器可以暂存消息，在设备上线时再推送，有一些特性很关键：

• offline

  允许设备暂时离线。

  即使是使用固定宽带，有些用户也会因为各种原因无法保持稳定的长连接，可能是上级路由设备有限制，或者是带宽被其它应用抢占而导致长连接不稳定。 将设备的在线状态与 TCP 长连接状态耦合在一起是不明智的。

• bridge

  设备连接在不同的 broker 上，通过 bridge 实现互通。

  支持几万台设备在线，估计一台 broker 就够了，但是一旦达到数十万、百万甚至上亿，肯定需要搭建 broker 集群，参见  The C10K problem。

简单起见， node.js 服务器端使用  mosca， 客户端使用  MQTT.js ，由于  mosca 不支持 bridge，本文不涉及 bridge 特性。

客户端与服务器通信

• 客户端通过服务器给自已发个消息

  server.js

  var mosca = require('mosca');
  
  var settings = {
      port: 1883
  };
  
  var server = new mosca.Server(settings);
  server.on('ready', function () {
      console.log('mosca server running');
  }).on('clientConnected', function (client) {
      console.log('client(' + client.id + ') connected');
  }).on('published', function (packet, client) {
      console.log('client(' + (client ? client.id : 'internal') + ') published topic(' + packet.topic + '): ' + packet.payload);
  }).on('subscribed', function (topic, client) {
      console.log('client(' + client.id + ') subscribed topic(' + topic + ')');
  }).on('unsubscribed', function (topic, client) {
      console.log('client(' + client.id + ') unsubscribed topic(' + topic + ')');
  }).on('clientDisconnecting', function (client) {
      console.log('client(' + client.id + ') disconnecting');
  }).on('clientDisconnected', function (client) {
      console.log('client(' + client.id + ') disconnected');
  });
  

  client.js

  var mqtt = require('mqtt');
  
  
  var client = mqtt.connect('mqtt://127.0.0.1:1883');
  client.on('connect', function () {
      client.subscribe('presence');
      client.publish('presence', 'a message from myself');
  }).on('message', function (topic, message) {
      console.log(topic + ': ' + message.toString());
      client.end();
  });
  

  运行  server.js

  $ node server.js
  mosca server running
  client(mqttjs_a423c0af) connected
  client(internal) published topic($SYS/41TXEHPDe/new/clients): mqttjs_a423c0af
  client(mqttjs_a423c0af) subscribed topic(presence)
  client(internal) published topic($SYS/41TXEHPDe/new/subscribes): {"clientId":"mqttjs_a423c0af","topic":"presence"}
  client(mqttjs_a423c0af) published topic(presence): a message from myself
  client(mqttjs_a423c0af) unsubscribed topic(presence)
  client(mqttjs_a423c0af) disconnected
  client(internal) published topic($SYS/41TXEHPDe/new/unsubscribes): {"clientId":"mqttjs_a423c0af","topic":"presence"}
  client(internal) published topic($SYS/41TXEHPDe/disconnect/clients): mqttjs_a423c0af
  

  运行  client.js

  $ node client.js
  presence: a message from myself
  $ 
  

客户端与客户端通信

• 客户端发送消息给另一个客户端

  下面的例子演示了客户端通过约定的  topic 互相通信。

  client_sub.js

  var mqtt = require('mqtt');
  
  var client = mqtt.connect('mqtt://127.0.0.1:1883');
  client.on('connect', function () {
      client.publish('sub', 'message from pub');
  }).on('message', function (topic, message) {
      console.log(topic + ': ' + message.toString());
      client.end();
  });
  

  client_pub.js

  var mqtt = require('mqtt');
  
  var client = mqtt.connect('mqtt://127.0.0.1:1883');
  client.on('connect', function () {
      client.publish('sub', 'message from pub');
  }).on('message', function (topic, message) {
      console.log(topic + ': ' + message.toString());
      client.end();
  });
  

  运行  server.js

  $ node server.js
  mosca server running
  client(mqttjs_ebdc9fd4) connected
  client(internal) published topic($SYS/4Jk9PBwDe/new/clients): mqttjs_ebdc9fd4
  client(mqttjs_ebdc9fd4) subscribed topic(sub)
  client(internal) published topic($SYS/4Jk9PBwDe/new/subscribes): {"clientId":"mqttjs_ebdc9fd4","topic":"sub"}
  client(mqttjs_ff000868) connected
  client(internal) published topic($SYS/4Jk9PBwDe/new/clients): mqttjs_ff000868
  client(mqttjs_ff000868) published topic(sub): message from pub
  client(mqttjs_ebdc9fd4) unsubscribed topic(sub)
  client(mqttjs_ebdc9fd4) disconnected
  client(internal) published topic($SYS/4Jk9PBwDe/new/unsubscribes): {"clientId":"mqttjs_ebdc9fd4","topic":"sub"}
  client(internal) published topic($SYS/4Jk9PBwDe/disconnect/clients): mqttjs_ebdc9fd4
  

  运行  client_sub.js

  $ node client_sub.js
  sub: message from pub
  $ 
  

  运行  client_pub.js

  $ node client_pub.js
  

客户端与客户端离线通信

离线通信需要同时满足以下条件

• 服务器配置持久存储

• 订阅方启用会话状态

  连接服务器时使用同样的 clientId 并指定  clean 为  false

• 发布方发布持久消息

  发布消息时指定  qos 大于  0 以及  retain 为  true

下面的例子演示了客户端接收离线消息

client_sub.js

var mqtt = require('mqtt');

var client = mqtt.connect('mqtt://127.0.0.1:1883', {clientId: 'sub', clean: false});
client.on('connect', function () {
    client.subscribe('sub');
}).on('message', function (topic, message) {
    console.log(topic + ': ' + message.toString());
    client.end();
});

client_pub.js

var mqtt = require('mqtt');

var client = mqtt.connect('mqtt://127.0.0.1:1883', {clientId: 'pub'});
client.on('connect', function () {
    client.publish('sub', 'message from pub', {qos: 1, retain: true});
}).on('message', function (topic, message) {
    console.log(topic + ': ' + message.toString());
    client.end();
});

运行  srever.js

$ node mqtt_server.js
mosca server running
client(sub) connected
client(internal) published topic($SYS/V19OSVfix/new/clients): sub
client(sub) subscribed topic(sub)
client(internal) published topic($SYS/V19OSVfix/new/subscribes): {"clientId":"sub","topic":"sub"}
client(sub) disconnected
client(internal) published topic($SYS/V19OSVfix/disconnect/clients): sub
client(pub) connected
client(internal) published topic($SYS/V19OSVfix/new/clients): pub
client(pub) published topic(sub): message from pub
client(sub) connected
client(internal) published topic($SYS/V19OSVfix/new/clients): sub
client(sub) subscribed topic(sub)
client(internal) published topic($SYS/V19OSVfix/new/subscribes): {"clientId":"sub","topic":"sub"}
client(sub) disconnected
client(internal) published topic($SYS/V19OSVfix/disconnect/clients): sub

运行  client_sub.js 订阅消息后退出

$ node client_sub.js 
sub: message from pub
$ 

运行  client_pub.js 发布消息

$ node mqtt_client_pub.js 

运行  client_sub.js 接收离线消息后退出

$ node client_sub.js 
sub: message from pub
$