MQTT-support

[kickster97]

WHAT is this pull request doing?

An MQTT-session inherits AMQP::Queue and extends with MQTT functionality.
MQTT exchange(topic) will only accept activity from an MQTT client, that will be responsible for routing messages to the MQTT-session.
The mqtt exchange handles MQTT routing keys etc. without needing to do conversions.

NOTE
The first version of MQTT Support does not support binding an AMQP exchange to and MQTT exchange. (Undefined behaviour if done)
In a separate PR we need to extract the AMQP exchange types into the AMQP namespace and in turn be able to differentiate between an AMQP::Destination and an MQTT::Destiantion when calling bind.
With that in place we will be able to safely do exchange to exchange bindings.

Docs for the website

HOW can this pull request be tested?

Specs have been migrated from Myra and fully cover the MQTT protocol, run with crystal spec.
Connect with mqtt client library of your choice and test your usage against this branch

[spuun]

I think you can (and maybe even should) build clean session by reusing the auto delete feature of queues.

[spuun]

About #803 (comment)

That connect spec passes, but for the wrong reason. Or well, the socket is closed but not because it receives the wrong packet type, but because of the bug that #803 will fix. When that bug is fixed i still think that the spec will pass, but for the right reason.

I guess the spec could be changed to send a PUBLISH instead (the packet must be greater than 8 byte to not trigger the bug).

[spuun]

After giving it a second thought I've concluded that we should change the spec to use some other packet type.

[kickster97]

After giving it a second thought I've concluded that we should change the spec to use some other packet type.

ok I will change the spec then! thanks :)

[carlhoerberg]

Often it's more efficient to yield than to capture and then call a block.