Two RestMulti enhancement ideas

[snazy]

I have two proposals to enhance RestMulti.

1. Produce multiple JSON objects, not just an array
2. Make requested demand configurable

I could contribute the necessary code changes.

Produce multiple JSON objects

Currently, PublisherResponseHandler.StreamingMultiSubscriber produces a JSON array, where each emitted item is encoded as a JSON array element. For some use cases it is easier to consume a bunch of "bare" JSON objects - i.e. just write the individual JSON objects, possibly separated by a newline. As an option, of course.

Proposal to add:

RestMulti.fromMultiData(multi).encodeAsArray(false)...

With encodeAsArray(false), the produced JSON would look like this:

{"some": "value"},
{"some": "value"},
{"some": "value"}

encodeAsArray(true) or omitting it would use the current behavior and produce something like this:

[{"some": "value"},
{"some": "value"},
{"some": "value"}
}

Configure request-demand

All implementations of PublisherResponseHandler.AbstractMultiSubscriber work with a hard-coded request-demand of 1, which means that every emitted item is "produced"/"computed" serially / one-after-the-other. If the computation of individual items takes somewhat longer, possibly waiting for remote resources to reply, it makes sense to use a higher demand to produce multiple items concurrently.

For example, if each item takes maybe 250 ms (requesting data from a remote source) to be produced, and 100 items are produced, it currently takes 25 seconds. With a higher concurrency it would take a fraction of that time. I.e. if the use case is known to be not CPU but (async) I/O bound, it might be legit/feasible to use a high demand.

Proposal to add:

RestMulti.fromMultiData(multi).withDemand( (long) 123 )...

Which would pass 123 as the demand for all call sites to Subscription.request in implementations of PublisherResponseHandler.AbstractMultiSubscriber.

[jamezp]

I'm guessing this should be for RESTEasy Reactive in Quarkus as RESTEasy doesn't have a RestMulti type.

[snazy]

Oh, that's actually true. I was probably misguided by the package name.
/cc @geoand WDYT?

[geoand]

@snazy sounds good!

Would you like to contribute these?

[snazy]

Sure! Let me open a PR against Quarkus in a bit.

[geoand]

💘

[snazy]

Closing as it's only related to Quarkus.