[bug] unable to publish with in memory mqemitter after some mqtt clients connected

System Information

• Aedes: 0.44.0
• NodeJS: 12.13.1
• OS: Ubuntu 18.04
• Arch: x86_64

Describe the bug

Unable to publish after clients connected and publish some messages while using default in memory mqemitter.

To Reproduce

Default mqemitter concurrency number is 100 in aedes so it happened when more clients connected, it’s easy to reproduce it when concurrency set to 2 .

Steps to reproduce the behavior:

1. $ git clone [e-mail]:JaosnHsieh/aedes-unable-to-publish.git
2. $ npm install
3. $ npm run server
4. $ npm run client

Expected behavior

No matter what concurrency number set to aedes, it should be able to publish message.

Additional context

I expect this._messageQueue length in mqemitter should decrease as time goes but it doesn’t.

Current work around I just change concurrency number to 10,000 so it always skip this condition.

I saw mqemitter exposed message queue length but didn’t see any code in aedes check this value.

[JaosnHsieh]

It’s a very basic functionality I suggest to check your code, the error is there, if your bug would be true no one could use aedes

it doesn’t happen too often due to default concurrency 100 which able to handle quite a lot of messages. Set to 2 for easier reproduce only.

Couldn’t see errors either on broker side or mqtt.js client side.

server.js

const Socket = require('net');
const Http = require('http');
const WSServer = require('websocket-stream');
const mqemitter = require('./mqemitter');
// mqemitter options same as aedes default but added console.log to this._messageQueue.length
const mq = mqemitter({
  concurrency: 2,
  matchEmptyLevels: true, // [MQTT-4.7.1-3]
});

const aedes = require('aedes')({
  mq,
});
const MQTT_PORT = 1800;
const WS_PORT = 3030;

aedes.on('publish', (publishPacket, client) => {
  console.log(`$ on publish`, publishPacket.topic, publishPacket.payload);
});

aedes.on('subscribe', (subscriptions, client) => {
  console.log(`$on subscribe from ${client.id}`, subscriptions);
  const topic = `test/${client.id}`;
  aedes.publish(
    {
      cmd: 'publish',
      qos: 0,
      topic: topic,
      payload: `${Math.random()}`,
      retain: false,
    },
    () => {},
  );
});

aedes.on('clientError', (...args) => {
  console.log(`$ clientError`, args);
});

aedes.on('connectionError', (...args) => {
  console.log(`$ connectionError`, args);
});

serverInit();

function serverInit() {
  const server = Socket.createServer(aedes.handle);
  const httpServer = Http.createServer();
  const ws = WSServer;

  server.listen(MQTT_PORT, () => {
    console.log(`MQTT Server is on port ${MQTT_PORT}`);
  });

  ws.createServer({ server: httpServer }, aedes.handle);

  httpServer.listen(WS_PORT, () => {
    console.log(`Websocket server is on ${WS_PORT}`);
  });
}

client.js

const mqtt = require('mqtt');

const MQTT_URL = `ws://localhost:3030`;
const clientNumber = 10;

go();

function go(number) {
  // let count = 0;
  for (let i = 0; i < (number || clientNumber); ++i) {
    const random6 = `${Math.random()}`.slice(2, 8);
    const randomId = `${random6}`;
    const client = mqtt.connect(MQTT_URL, {
      clientId: `${randomId}`,
      username: `${randomId}-username`,
      password: `${randomId}-password`,
    });
    client.on('connect', (connack) => {
      const topic = `test/${randomId}`;
      client.subscribe(topic, { qos: 0 }, function (err, granted) {
        if (err) {
          console.log('$ subscribe err', err);
        }
        console.log(`$ subscribed to ${topic}`);
      });
    });
    let isReceivedMsg = false;
    client.on('message', function (topic, payload) {
      isReceivedMsg = true;
      console.log(`$ on message`, topic, payload);
      go(1);
    });
    client.on('error', (...args) => {
      console.log(`$ error`, args);
    });
    setTimeout(() => {
      if (isReceivedMsg === false) {
        console.log(`$ didn't receive message, unable to publish`);
      }
    }, 2000);
  }
}

Share with someone who also encountered same issue.

[robertsLando]

Closing as dup of #666