# MQTT topic: CBOR conversion
**URL:** https://discourse.nodered.org/t/mqtt-topic-cbor-conversion/29151
**Category:** General
**Created:** [29 June 2020 08:55 UTC](https://discourse.nodered.org/t/mqtt-topic-cbor-conversion/29151 "2020-06-29T08:55:41Z")
**Posts on this page:** 7
**Page:** 1
### Author:  [@kalpino](https://discourse.nodered.org/u/kalpino)
#### Post date: [29 June 2020 08:55 UTC](https://discourse.nodered.org/t/mqtt-topic-cbor-conversion/29151/1 "2020-06-29T08:55:41Z")
Hello,
I have a topic that publishes data in CBOR format. I installed the CBOR block so that I can convert data from CBOR to JSON.
When I try to show the converted message in the debug panel, I always get an empty message.
Where am I going wrong?
Here is the nodes I'm using.
Thanks
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### Author:  [@knolleary](https://discourse.nodered.org/u/knolleary)
#### Post date: [29 June 2020 09:10 UTC](https://discourse.nodered.org/t/mqtt-topic-cbor-conversion/29151/2 "2020-06-29T09:10:52Z")
I don't know if anyone here has any experience of the CBOR node, so I doubt you'll get a direct answer.
But we can help you try to figure it out.
I assume you mean `node-red-contrib-cbor` - it is barely complete node, with no help text.
Looking at its code, I can see it will only decode `msg.payload` if it's a Buffer type object. So the question what is the MQTT node passing it. You can configure the MQTT node to always send a Buffer type object - I suggest you do that it you haven't already. It's always worth adding a Debug node so you can check exactly what you are passing into the CBOR node.
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### Author:  [@kalpino](https://discourse.nodered.org/u/kalpino)
#### Post date: [29 June 2020 09:14 UTC](https://discourse.nodered.org/t/mqtt-topic-cbor-conversion/29151/3 "2020-06-29T09:14:15Z")
I already have the MQTT block passing a buffer. Also, using a debug node I can see that the output of the mqtt block is an array of cbor-encoded data.
What I expect as an output of the CBOR node is data in JSON format but all I get is an empty payload.
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### Author:  [@knolleary](https://discourse.nodered.org/u/knolleary)
#### Post date: [29 June 2020 09:17 UTC](https://discourse.nodered.org/t/mqtt-topic-cbor-conversion/29151/4 "2020-06-29T09:17:55Z")
Given how little code is in the node ([https://github.com/DoNck/node-red-contrib-cbor/blob/master/node-red-contrib-cbor.js](https://github.com/DoNck/node-red-contrib-cbor/blob/master/node-red-contrib-cbor.js)), there's not much I can see to go wrong, assuming its using the `cbor` library properly.
At this point, you'd need to raise an issue against the node so its author can provide some assistance - [https://github.com/DoNck/node-red-contrib-cbor/issues](https://github.com/DoNck/node-red-contrib-cbor/issues)
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### Author:  [@dceejay](https://discourse.nodered.org/u/dceejay)
#### Post date: [29 June 2020 09:25 UTC](https://discourse.nodered.org/t/mqtt-topic-cbor-conversion/29151/5 "2020-06-29T09:25:31Z")
If it is already a buffer then I'm not sure why they need to do this
`msg.payload=cb.decode(new Buffer(msg.payload));`
[https://github.com/DoNck/node-red-contrib-cbor/blob/master/node-red-contrib-cbor.js#L12](https://github.com/DoNck/node-red-contrib-cbor/blob/master/node-red-contrib-cbor.js#L12) .
Also there are some limit on object size on the underlying library - [https://www.npmjs.com/package/cbor](https://www.npmjs.com/package/cbor) - so how big is the object you are trying to decode ?
Certainly a simple object -\> cbor -\> object seems to work ok. but maybe there are extra encodings in the cbor buffer you have ? see [https://github.com/hildjj/node-cbor#supported-types](https://github.com/hildjj/node-cbor#supported-types)
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### Author:  [@kalpino](https://discourse.nodered.org/u/kalpino)
#### Post date: [29 June 2020 10:06 UTC](https://discourse.nodered.org/t/mqtt-topic-cbor-conversion/29151/6 "2020-06-29T10:06:07Z")
The CBOR block works fine. My problem is probably due to the fact that CBOR encoded data in input to the block were not encoded from a JSON but from an array of data.
I will probably have to change the block so that it can decode data that is not in JSON format.
Thanks!
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### Author:  [@system](https://discourse.nodered.org/u/system)
#### Post date: [13 July 2020 10:06 UTC](https://discourse.nodered.org/t/mqtt-topic-cbor-conversion/29151/7 "2020-07-13T10:06:07Z")
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