Requirement: Document what happens if a Consumer tries to unsubscribe but no subscription exists

[RobWin]

While implementing the unsubscribeEvent I'm actually unsure how it is specified in WoT.
If a consumer unsubscribes from an event where it has never subscribed to. Would you expect a error message or should it be an idempotent operation and not return an error message?
It's the same discussion like in a HTTP DELETE call. Usually I prefer to make DELETE idempotent and not throw a error if the resource is already deleted.

I would prefer to not throw an error message when there is no event subscription.
While implementing it, I definitely think that some sort of acknowledgement message after a subscription or unsubscription would make sense.

[benfrancis]

@RobWin wrote:

If a consumer unsubscribes from an event where it has never subscribed to. Would you expect a error message or should it be an idempotent operation and not return an error message?

I don't have a strong opinion but I tend to agree that this doesn't necessarily need to throw an error.

Either way it would be good to document this in the specification, either as a normative requirement if an error is expected or as a Note if none is expected.

I definitely think that some sort of acknowledgement message after a subscription or unsubscription would make sense.

I see you filed #29 for this, thanks.