Peter M. Groen / FlashMQ

Also add a test to test all scenarios.

This also fixes session clean_start, which was never done since the
MQTT5 refactor to clean_start (vs clean session).

It timed out sometimes. When it works, it doesn't even take longer,
because it's just the timeout.

It was caught by an assert. In release mode, this simply meant
subscribing to 0 still gave you QoS messages.

Fixes assertion error in debug only.

It was flakey. I also ported it to the new test client.

The order packets would (mostly) arrive, is 'retained publish', then
'sub ack'. This is now fixed.

This also stablizes test_retained_changed(). The test was also
refactored to use the new test client.

This prevents confusion when another instance of FlashMQ is running.

This is not the final way. For instance, when SSL connections will also
be tested, this won't work anymore.

Now that parsing and handling of packets is separated, we can use the
main code to parse packets in the new FlashMQTestClient. This allows
great flexibility in inspecting the server response in a flexible
manner.

We now also have the ability to make tests for MQTT5 features.

This is necessary for the test client I have in mind, so I can re-use
this code in that new test client which has no MQTT behavior, but just
returns packets (meaning I have to be able to parse them without
initiating handling).

This needed a separation: getting the current thread, and getting the
thread of the client you're queueing a command for.

This also resolves a circular reference between Client and ThreadData.

Instead of the thread data, which didn't make sense.

This required adding a global stats object.

It also contains a bit of refactor to make a type out of the derived
counters.

This makes much more sense than returning the amount of messages sent
all the way up the call stack.

It tested the wrong thing. Tests still pass.

This allows easier saving of MQTT5 properties, for which a new file
version for retained messages is created. It uses the packet parsing logic.

Because clients can now also exist as dummy objects, I had to add some
extra checks.

Also split up handlePublish() and the new parsePublishData().

Only mqtt3 though.

I need to decide what to do with getPublishData

and that disabled test needs repurposing.

The behavior for MQTT3 clients in the same, but I replaced the term
'clean session' and described the behavior in MQTT5 terms, of 'clean
start' and an expiry interval.

For the coming MQTT5 support, I'll need this a lot.

This is a preparation for MQTT5, because when there are receivers and
publishers with different protocols, you can't always just write out the
same packet. You can sometimes though, so that's what the copy factory
determines.

This doesn't actually fix a real bug, just makes assumptions clear.

Because that's what's it is now.

A lot of code can be refactored to get the settings from this now, but
I'm not going to do that yet.

This entails making copies of the original packet when necessary,
because QoS 0 doesn't have a packet id. I tried to keep it to an
absolute minimum and do some precarious optmizations for it. There are
tests though.

It caused really funky behavior. When a destructed client closed fd 0,
eventfd() would give 0 back as fd. This would then later give errors.

Committing separately, because I want to be able to revert the fix I'm
about to commit.

There were bugs in which authentication object was used when, causing
threadings bugs. Instead of getting from the 'sender', we can just store
a thread local pointer.