CODEWITHSUNDEEP
node.jsmqtt
procatmer
procatmer

Reputation: 5649

Is it possible to publish a file into MQTT server?

I have a mini microservice project using NodeJS as backend and MQTT as the media for communicating between services. and I have a service that suppose to send an excel file to another service. Is there any way for MQTT to publish a file?

So far I only managed to send it as binary-data but had no idea what to do with that, or is there any way to recreate a file from binary-data in NodeJS?

Upvotes: 3

Views: 5689

Answers (3)

procatmer
procatmer

Reputation: 5649

since mqtt payload has limit, as @Fabio Manzano cited above, and it is impossible to publish binary data from even a small-sized file, i think i've managed to make this work by breaking it down into chunks (the binary data) and publish them separately. then merge them all back again when it finishes sending the last chunk.

and then do like what this thread suggests:

Writing image to local server

i've tried it and it succeed. thank you for the responses.

Upvotes: 1

Fabio Manzano
Fabio Manzano

Reputation: 2865

This stackoverflow thread talks about MQTT byte limits.

The length of the actual topic string is at most 65536 bytes. This is a limit imposed by the mqtt spec, you can't change it. It is also worth noting that the topic is encoded with utf-8, so you may have less than 65536 characters available. The payload of the message is limited to 268,435,456 bytes. Again, this is defined by the spec.

If you exceed these limits, you need to break your file in chunks and use Base64 algorithm to encode them to ASCII. Make sure you send a hash of the whole file to check and guarantee that your file is consistent in the other side of the wire, after restoration.

This article does something similar using Python, in case you want to see some code. Hope it helps!

Upvotes: 3

hardillb
hardillb

Reputation: 59866

A file is just binary data and MQTT payloads are just binary data.

If you want to include meta data, e.g. a file name then you are going to have to come up with a data format to encode the filename along with the files content. That can be done any number of ways, be it in the topic you publish or by creating a data structure that includes the filename and the contents of the file.

Upvotes: 2

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