Add the ability to update the input for a WorkflowHost.

[zach-klippenstein]

Closes #247.

[zach-klippenstein]

Would it be more useful, instead of requiring an initial input immediately and having an update function, to just only accept a stream of inputs? The workflow would then just not start until the first input was emitted.

[rjrjr]

Would it be more useful, instead of requiring an initial input immediately and having an update function, to just only accept a stream of inputs? The workflow would then just not start until the first input was emitted.

Yes! We've been longing for that in production already.

If you're still on board with that notion I'll hold off on reviewing this for real.

[zach-klippenstein]

Totes. I'll update the PR asap.

[zach-klippenstein]

@rjrjr Updated the API. WorkflowViewModel now uses the new flatMapWorkflow operator in workflow-rx2-runtime to convert a stream of inputs into a stream of outputs. Should inputs be an Observable conveted to a Flowable with BackpressureStrategy.BUFFER internally instead?

[zach-klippenstein]

Also, maybe the stream operator is too much - could just make an extension function on Factory that takes an input stream and just returns a WorkflowHost. I just like the operator because the API surface is so tiny and it hides all the channel machinery completely.

[rjrjr]

Should inputs be an Observable converted to a Flowable with BackpressureStrategy.BUFFER internally instead?

You mean on WorkflowViewModel, right? Flowable certainly seems like the right thing on the runtime API. WorkflowViewModel isn't public either, though. My gut is to keep that working in terms of Flowable, and make WorkflowActivityRunner take an Observable.

Also, maybe the stream operator is too much - could just make an extension function on Factory that takes an input stream and just returns a WorkflowHost. I just like the operator because the API surface is so tiny and it hides all the channel machinery completely.

No no no, I think it's a keeper. Such a natural way to think about this.

[rjrjr]

This is gorgeous.

[zach-klippenstein]

This formatting is the auto-formatter being stupid.

[zach-klippenstein]

A bunch of tests broke in interesting ways because things are more asynchronous now. Added WorkflowTester.awaitFailure and .withFailure to make testing errors more reliable.