javascript - MQTT.js 订阅从代理接收多条相同消息

Question

我在CloudMQTT上运行，我的JS代码是这样的:

var mqtt_url = URL.parse('mqtt://m10.cloudmqtt.com:15272' || 'mqtt://localhost:1883');
var auth = (mqtt_url.auth || ':').split(':');
var url = "mqtt://" + mqtt_url.host;

var options = {
  port: mqtt_url.port,
  clientId: 'mqttjs_' + Math.random().toString(16).substr(2, 8),
  username: USERNAME,
  password: PASSWORD,
};

// Create a client connection
var client = mqtt.connect(url, options);

client.on('connect', function() { // When connected

  // subscribe to a topic
  client.subscribe('relay', function() {
    // when a message arrives, do something with it
    client.on('message', function(topic, message, packet) {
        // console.log(packet);
      console.log("Received '" + message + "' on '" + topic + "'");
    });
  });

  // subscribe to a topic
  client.subscribe('photoresistor', function() {
    // when a message arrives, do something with it
    client.on('message', function(topic, message, packet) {
      console.log("Received '" + message + "' on '" + topic + "'");
    });
  });

  // publish a message to a topic
  client.publish('relay', value, function() {
    console.log("Message of ", value, " is published");
    // client.end(); // Close the connection when published
  });

});

我将 ESP8266 连接到光敏电阻，并且它每 5 秒将光敏电阻值发布到 photoresistor 主题。

好吧，每 5 秒我就会在我的 Node 服务器 (MeteorJS) 上收到四个相同的控制台日志。

I20170907-19:33:51.421(-4)? Received '156' on 'photoresistor'
I20170907-19:33:51.423(-4)? Received '156' on 'photoresistor'
I20170907-19:33:51.424(-4)? Received '156' on 'photoresistor'
I20170907-19:33:51.425(-4)? Received '156' on 'photoresistor'
I20170907-19:33:57.741(-4)? Received '39' on 'photoresistor'
I20170907-19:33:57.742(-4)? Received '39' on 'photoresistor'
I20170907-19:33:57.743(-4)? Received '39' on 'photoresistor'
I20170907-19:33:57.743(-4)? Received '39' on 'photoresistor'
I20170907-19:34:05.465(-4)? Received '37' on 'photoresistor'
I20170907-19:34:05.467(-4)? Received '37' on 'photoresistor'
I20170907-19:34:05.468(-4)? Received '37' on 'photoresistor'
I20170907-19:34:05.470(-4)? Received '37' on 'photoresistor'
I20170907-19:34:10.665(-4)? Received '161' on 'photoresistor'
I20170907-19:34:10.667(-4)? Received '161' on 'photoresistor'
I20170907-19:34:10.667(-4)? Received '161' on 'photoresistor'
I20170907-19:34:10.668(-4)? Received '161' on 'photoresistor'

知道什么可能导致 client.subscribe 函数或 CloudMQTT 输出多条相同消息吗？

Answer 1

似乎在某些情况下，在连接事件处理程序内订阅可能会导致重复订阅。 mqtt.js release 2.9.0 中解决了这种性质的问题。 ，如上所述here 。 因此，升级到最新的 mqtt.js 版本(当前为 2.13.1)可能会解决您的问题。

但是，另请注意 mqtt.js usage notes声明“从 v2.0.0 开始，如果 clean: true，订阅将在重新连接时恢复”。另请参阅here 。如果是这样，您似乎实际上根本不需要从连接事件处理程序中进行订阅，这有望从一开始就防止重复订阅的发生。

您应该可以在连接 Node.js 客户端时重新启动 CloudMQTT 代理来测试上述假设。这是否会导致您开始看到重复的消息？如果是这样，我相信补救措施确实是将您的订阅移到连接事件处理程序之外。