Mqtt.js: "Could not determine host" on mqtt.connect() in a WebWorker

Created on 14 Sep 2016 · 7Comments · Source: mqttjs/MQTT.js

Hi guys,

Awesome work with MQTT.js! I currently use it with mosquitto 1.4.10.

I have a use case where I am publishing around 10-20 times per second from the chrome client, mostly from metrics, which is not urgent. I noticed that the messages are being queued before sending it out, to the tone of around 10 publishes per second max. (I tested this using setInterval()) Thus, when I need to send something out that is urgent, the queue causes the publish to happen much later (delay is proportional as the queue gets longer).

To solve this issue, I offloaded the MQTT publishes to a web worker, which runs its own MQTT connection (using importScripts('/js/browserMqtt.min.js') and its own mqtt.connect(brokerUrl)).

However, I am getting the error Could not determine host. Specify host manually. I worked around this by specifying at the top (in the worker script): var document = { URL: null } and then setting document.URL = url on worker.postMessage().

Sorry for the long post. Few questions:
1) Is the 10 publishes per second cap a known thing? I know javascript in single-threaded, not sure if this something I configured wrong or a MQTT.js limitation.
2) Is the var document = { URL: null } the correct hack to get MQTT working on a Web Worker?

Thanks again!

Source

hijklmno

Most helpful comment

@OmgImAlexis feel free to close the old ones anyway :)

mcollina on 11 May 2020

👍2

All 7 comments

Hey @hijklmno I started a little project a while ago mqttWorker to provide the same api MQTT.js API but do all MQTT work in a WebWorker. The project is not ready but you can have a look at it.

To fix the var document.URL I just create the document in the beginning of the Worker see mqttWorker.js#L25, so your fix is the same.