MQTT Additional Header/Payload

General
1

Hi guys,

First time working with MQTT and I'm excited how easy it was to setup the broker and configure 2 Clients in Node-Red to connect.

First a general question: Is it possible to send more than the "payload" via MQTT e.g. an additional Header?

In my case I receive an HTTP Call with a payload , which I send to the MQTT Broker. But I also need one of the objects from msg.res.xxx.xxx (doesn't really matter) to be send in the same call to the broker.
I tried to just add the field to the payload via a function node, but on the subscribed client side just the "original" payload is received.

Function node:
var payload=msg.payload; //get payload
var parsedUrl=msg.req._parsedUrl.search;
msg.payload.parsedUrl=parsedUrl;
return msg;

Flow:
image

Any idea?

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2

Hi again,

It seems that I can't change the payload due to the format? As changing the topic or adding another field is working fine.
So rephrasing my question a little bit:
Can I add an additional object send via MQTT. Something like "msg.header" or "msg.payload2" :smiley:

Or how to change the payload format? Trying to convert it to JSON String gives me the error "Ignored non-object payload"

Thanks in advance for your help.

3

MQTT messages are generally a string sent to a specific topic. But you can send a json formatted object via mqtt and encode or decode it with the help of the json node.

4

No, but whatever you put in msg.payload should be sent to mqtt. Try this in your function node

msg.payload = {response: msg.payload, url: msg.req._parsedUrl.search
return msg;

Or you can do the same thing in a Change node.
However, I don't see msg.req._parsedURL.search in your debug output, are you sure you don't mean msg.req.url?

5

Thanks for your reply.
Yes, the msg.req._parsedUrl.search was just not on the screenshot.

If I use your code in the function node, no msg is getting out of the node. (checked with a debug node)

msg.payload = {response: msg.payload, url: msg.req._parsedUrl.search}
return msg;

UPDATE: Sorry, my mistake. Works! :slight_smile: