Help with REGEX transformation for mqtt channel

Setup, Configuration and Use Beginners
1

I have a mqtt channel and i use a chained tranformation to extract a temperature setpoint value

REGEX:(.*ATCExpect0.*)∩JSONPATH:$.NSPanel.ATCExpect0

so for a payload like

{"NSPanel":{"ATCMode":0,"ATCExpect0":20}}

i get the number 20.So far so good
A weird bug happens to the device(tasmota) and when it is set to “21” the payload goes like this

{"NSPanel":{"ATCMode":0,"ATCExpect0":21}B}}

an extra }B ruins the payload and i get log error

[WARN ] [t.generic.ChannelStateTransformation] - Executing the JSONPATH-transformation failed: An error occurred while transforming JSON expression.

I read REGEX documentation and so i tried several versions of my incoming transformation like

REGEX:(.*ATCExpect0.*)∩REGEX:(s/}B}/}/)∩JSONPATH:$.NSPanel.ATCExpect0

with no success…Any ideas?

2

You’re probably going to have to resort to a JS transformation or a rule to process these messages. For what ever reason tasmota is sending invalid JSON and the REGEX transformation probably won’t get you to where you can correct it.

3

can you point me to an example how to remove }B characters with a JS transformation?I read the documentation but cant found out where to start…

4

That specifically? Not really. It’s standard ECMAScript 5.1 so any JavaScript tutorial on how to process strings will do. Put that into a filename.js file under $OH_CONF/transform and wrap your code un a function like the example in the docs.

(function(i) {
    // Your code goes here
    return value;
})(input)
5

Remove the parentheses for the substitution:

REGEX:(.*ATCExpect0.*)∩REGEX:s/}B}/}/∩JSONPATH:$.NSPanel.ATCExpect0
1 Like
6

thnx mate it is working fine now!