Setting OpenTelemetry baggage

[rtimush]

Hi,

I'm struggling to find a way to set OpenTelemetry baggage.

BaggageExt trait let's me create a new Context with an updated baggage, but I haven't found a way to attach the Context to the current span. I can use set_parent to update the parent span context, but I haven't found a way to get the original parent context.

The following code almost works (it sets the baggage), but it makes a span reference itself as a parent, which is also wrong.

Span::current().set_parent(Span::current().context().with_baggage(baggage));

Do I miss something, or is it just not supported yet?

[mladedav]

There's no support for baggage in this crate.

However, from my understanding, you cannot change a span's context in OpenTelemetry which includes adding baggage. There is a context when you create the span and it is immutable so I think that the closest thing to that is what you're doing except that you actually create a new span:

let span = debug_span!("new_span");
span.set_parent(Span::current().context().with_baggage(baggage));
let _guard = span.entered();

But maybe I'm misunderstanding the otel spec.

[rtimush]

Yes, thanks, I ended up doing something like this. It is not perfect, as you have to be able to get the Context of the parent span, which is not always easy, but it works.

[mladedav]

I think you should be able to get the context every time, if you're creating spans with parents based on current span, you can get the current span and then its context and if you're setting parents manually, you already have the parent so you can extract the context from there.

I think the only issue would be if you're setting parents manually but only have SpanId and not the whole Span for some reason. Is that your case or is there another issue?

[rtimush]

It's easy to get the parent context if I'm the one creating the span, but not if the span is already created and entered (for example by a tower layer).

[mladedav]

I thought Span::current().context() would work in that case?

[rtimush]

It will give the context of the current span, while I need a context of the parent one to be able to use set_parent.