Validate event/reading value descriptors in export-distro

[chenchix]

Fede and I were thinking about this feature and why it is in export distro instead of core-data, which is the entity that sends the messages.

In our understanding, core-data should send only valid messages and export only take care of filter, discard...

What do you think?

[feclare]

We have been looking at this and we would like to propose to implement it in data. We can check if the values are correct depending on their value descriptor and drop them without storing.

Some questions:

• core-data had a flag (configuration.Metadatacheck) to drop events with invalid deviceId. Should the same flag be used to verify readings? Or it is better to create a new flag configuration.Readingcheck?
• What happens to a event with an invalid reading and another valid? drop the whole event? drop one reading?
• What happens to a event with an invalid reading? drop the whole event?
• Should we move this issue to another repo (core-go or edgex-go)?

Any feedback @jpwhitemn ?