When does DeliveryToken return from .wait()

[dlips]

Hello,

I am trying to check if my QoS 1 messages were delivered to my broker. From the documentation it is not clear to me, when the call to DeliveryToken::wait will return. Is it immediately when the message was sent to the broker or after the broker has successfully sent an ACK for that message?
In the C library you can register a callback for this with MQTTAsync_setDeliveryCompleteCallback(), see here but I cannot find the equivalent callback registration on the async_client. Is this planned to be implemented or does somebody know a workaround?

[fpagliughi]

The token completes when the transaction is finished, So:

• QoS 0, completes immediately.
• QoS 1, completes when the PUBACK is received
• QoS 2, completes when the PUBCOMP is received

I didn't expose all the callbacks because I have trying to move the library away from requiring them. Although they still make sense in C, they seem to make much less sense in a Rust async world. And they are extremely problematic with their limitations (no blocking calls) and tread synchronization issues.

But I could probably add the missing ones to make a full consistent API before moving on to a v2.0 that is more purely async/await.

I thought the MQTTAsync_setDeliveryCompleteCallback() was a bit redundant. I believe it could be done more uniformly by providing succes/failure callbacks, similar to the connect_with_callbaks().

For the moment, the solution is to spawn a task to wait on the Token (which implements the Future trait), and then fire a callback, if that's what you want.