Missing examples with reactive programming (reactor)

[ygiros]

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

[trask]

hi @ygiros! there are no docs, but check out the io.opentelemetry.instrumentation:opentelemetry-reactor-3.1 library which has some helpful utilities for propagating context in project reactor:

https://github.com/open-telemetry/opentelemetry-java-instrumentation/tree/main/instrumentation/reactor/reactor-3.1/library/src/main/java/io/opentelemetry/instrumentation/reactor/v3_1