LoRaWAN unprocessable messages also contain unknown messages

[BobClaerhout]

The metric hono_telemetry_payload_bytes_count contains a status field. This field is either forwarded, unprocessable or undeliverable. We added prometheus alerts to follow up unprocessable messages in the lora adapter. However, in the lora adapter we are getting status unprocessable when the LNS is providing a message that is not an uplink message. This is completely different from an actual uplink message that is unprocessable because of any other unexpected exception. For this we would like to add an additional status: unknown, indicating that the message we received is an unknown message and thus not implemented which is fundamentally different from unrpocessable messages.

[sophokles73]

I would argue that there might be different reasons for why a message cannot be processed. The message might not adhere to the supported/expected syntax or there might be a problem while processing the message due to e.g. a failing back end service. In both cases the messages are unprocessable. So, what we are talking about here seems to be having a way to also indicate the reason why a message could not be processed.

Having a fourth status unknown does not really serve this purpose FMPOV as it seems to suggest that the message does not fall into the unprocessable category (which it still does). Also, changing the semantics of the unprocessable status in this way may lead to existing alarms failing to detect this situation, if the corresponding messages no longer are being tagged as unprocessable.

Another less intrusive solution might be to add another tag for indicating the cause explicitly. This tag could then have values like bad-syntax, unsupported etc. while the status tag would still have value unprocessable

WDYT?

[BobClaerhout]

I agree with your reasoning.

I would suggest reason to be the additional tag.
Furthermore, I would suggest following values:

• bad-syntax: json could not be converted
• unknown-type: type of the message could not be deducted
• unsupported-type: type of the message is not supported for uplink
• unknown: reason could not be deducted from the error