Missing examples with reactive programming (reactor)

Hi,

Examples provided in Manual span creation and baggage propagation are only available with imperative programming. Is it possible to extend those examples to reactive programming ?

Zero-code instrumentation with opentelemetry agent specifies compatibility with reactor library https://github.com/open-telemetry/opentelemetry-java-instrumentation/blob/main/docs/supported-libraries.md#libraries--frameworks, however I didn't find any examples here or in https://opentelemetry.io/docs/ on how to do manual instrumentation on reactive code with reactor.

I would like to execute following actions in reactor operators

• Create span and make it current
• Inject attribute to current span
• Inject baggage and make it current

As for now, I can only "guess" how I should do in reactive programming, by "translating" imperative examples I have found with reactor equivalents.

For example I translate following imperative code

public String imperativeFoo() {
    try (Scope scope1 = tracer.spanBuilder("foo").startSpan().makeCurrent()) {
        Span.current().setAttribute("fooAttribute", "fooAttributeValue");

        Baggage baggage = Baggage.current().toBuilder()
                .put("fooBaggage", "fooBaggageValue")
                .build();

        try (Scope scope2 = baggage.makeCurrent()) {
            return bar();
        }
    }
}

private String bar() {
    // returns "bar:fooBaggageValue"
    return "bar:" + Baggage.current().getEntryValue("fooBaggage");
}

into

public Mono<String> reactiveFoo() {
    return Mono.using(
        () -> tracer.spanBuilder("foo").startSpan().makeCurrent(),
            scope1 ->
                Mono.fromSupplier(() -> Baggage.current().toBuilder().put("fooBaggage", "fooBaggageValue").build())
                    .doOnNext(baggage -> Span.current().setAttribute("fooAttribute", "fooAttributeValue"))
                    .flatMap(baggage ->
                        Mono.using(
                            baggage::makeCurrent,
                            scope2 -> Mono.fromSupplier(this::bar))));
}

private String bar() {
    // returns "bar:fooBaggageValue"
    return "bar:" + Baggage.current().getEntryValue("fooBaggage");
}

But is it the right way to do it ? If yes, could you please add this example to the documentation ?

Did I miss some other documentation on it somewhere ?

Thanks

Start with the examples in the manual-tracing directory and compare them with the Reactor compatibility noted in supported-libraries.md and the OpenTelemetry documentation. Verify whether the proposed Mono-based scope and baggage handling is correct, then add a reactive manual-instrumentation example if the repository has a suitable documentation location. Done means the example clearly demonstrates the three requested actions and its behavior is documented.