Reactor: ContextPropagationOperator should allow retrieval from ContextView

[philsttr]

Is your feature request related to a problem? Please describe.

Starting in reactor 3.4+, to read from the subscriber context, reactor provides a read-only object of type reactor.util.context.ContextView.

Prior to 3.4, reactor provided a read-write object of type reactor.util.context.Context when reading.

Currently, ContextPropagationOperator.getOpenTelemetryContext takes an object of type reactor.util.context.Context. Unfortunately this method cannot be used easily with reactor 3.4+, since an object of type reactor.util.context.Context is not available when reading values from the context.

Describe the solution you'd like

I'd like ContextPropagationOperator to provide an efficient method of reading values from a reactor.util.context.ContextView.

Having said that ContextPropagationOperator needs to continue to work with older reactor versions that do not have reactor.util.context.ContextView.

Describe alternatives you've considered

Create a Context from a ContextView, and pass that to ContextPropagationOperator.getOpenTelemetryContext. Potentially creates garbage.

Iterate over values in ContextView looking for one whose key.toString().equals("otel-trace-context"). Inefficient.

[mateuszrzeszutek]

Hey @philsttr ,

Thanks for filing this! This definitely makes sense to me 👍

Reactor introduced ContextView in 3.4 -- we'll have to bump the minimum supported version to 3.4, and probably add a new common module for the code that's shared between the library (now 3.4) and javaagent (still 3.1) instrumentation.