MQTT error handling

[elecaude]

In the case of observations inserted via MQTT it would be interesting to have a specific MQTT topic for error handling.
Currently, we can just know the new observations inserted by subscribing to the insertion topic but in case of error, we have no information.

[hylkevds]

MQTT has no way to send messages to a single user. So when an insertion over MQTT fails, there is no way for the server to tell the user. This is something that is possible for the new MQTT version 5 that was recently released. There is an issue for STA v2.0 that addresses this.

Adding an error topic is not that useful. It would be hard to figure out which error was caused by which insert attempt. It would also potentially expose sensitive information to all users.

At the moment, if data is important, it is best to use HTTP for inserts.

[sgrellet]

Link OGC GitHub: opengeospatial/sensorthings#5

[sgrellet]

Could be worked out in a MQTT 5 extension then submitted to the SWG

[sgrellet]

15-078r6 has a direct dependency to MQTT 3.1.1 (even if not mentionned in the 'References' section of the standard) : see
http://www.opengis.net/spec/iot_sensing/1.0/req/create-observations-via-mqtt