Issues parsing json payloads in MQTT
# umh-supportt
trentc
02/14/2025, 8:16 PMIssues parsing json payloads in MQTT protocol converter...
trentc
02/14/2025, 8:22 PMHere is the topic and payload of the input...
https://cdn.discordapp.com/attachments/1340054203422212186/1340055636662161449/image.png?ex=67b0f790&is=67afa610&hm=294ed7409b92e374adab15a422c7d1ce7a8c30931b13a5143fbb6cec4bcbb02d&
trentc
02/14/2025, 8:23 PMHere is the processor....
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# these variables are autogenerated from your instance location
let enterprise = "MACH-Controls-LLC"
let site = "Dallas"
let area = "Booth-18"
let schema = "_local"
# Get MQTT Topic, replacing spaces in topic with _
let topic = meta("mqtt_topic").replace_all(" ", "_")
# Set the tagname to be from the 4th level
# Excluding the last 2 levels.
# Including any levels between, but joining them with '.'
# By default the last level is not included in the 'slice" function.
let tagname = $topic.split("/").slice(4,-1).join(".")
# Set the payloadTagName to be the last level of the topic
let payloadTagName = $topic.split("/").index(-1)
value = content()trentc
02/14/2025, 8:24 PMThe result....
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{
"Production": "{\"timestamp_ms\":1739564659054,\"schema\":\"production\",\"ProdState\":1,\"TotalParts\":6824,\"RejectParts\":370}",
"timestamp_ms": 1739564659374
}trentc
02/14/2025, 8:50 PMMy solution was to just use node red to republish on the appropriate _historian topic and it consumes the payload perfectly.
Something with the bloblang is mucking it up.
I believe something in the post processing, after my processor is adding the escape characters, because I can't seem to get rid of them in my processor.
d
Diederik
02/15/2025, 1:16 PMyou could try to use the javascript language instead of the bloblang? (i have not done it myself) but it should be easier i suppose/maybe you will yield a better result?
t
trentc
02/15/2025, 1:56 PMThat’s definitely something I want to explore, I just found out about this being released….but don’t have time to revisit before the conference next week.
Regardless, why can’t I just pass in a payload value that already meets the schema and it get consumed appropriately..?
j
Jermuk
02/15/2025, 7:33 PMyou could try passing it on using a mqtt-to-kafka bridge? or in general with a custom data flow compomemt? the bloblang protocol converters dont support it, (just understood that you were not using ndered_js yet)
Jermuk
02/15/2025, 7:33 PMfor nodered_js, use the validate button
Jermuk
02/15/2025, 7:33 PMthen copy paste verything incl. benthos-umh documentation into chatgpt
Jermuk
02/15/2025, 7:33 PMeven 4o will gfive you a good result
t
trentc
02/16/2025, 11:58 PMHow do i use a mqtt to kafka bridge for a different mqtt broker as the source? With a custom component?
trentc
02/17/2025, 12:00 AMThis is effectively what I did, I just used node red to republish to the umh broker at an _historian topic…. But i was bridging broker to broker.
j
Jermuk
02/17/2025, 7:59 AMyes!