ZIO Traces not child of tapir endpoint span

tapir
1

Hi all,

Using ZIO and open telemetry IMHO I have to provide an Interceptor propagates OpenTelemetry’s `io.opentelemetry.context.Context` (ThreadLocal) into zio-opentelemetry’s `ContextStorage` (FiberRef) for each Tapir request, so that `zio.telemetry.opentelemetry.tracing.Tracing` spans (e.g. `tracing.span`) are children of the HTTP sttp.tapir.server.tracing.opentelemetry.OpenTelemetryTracing `SERVER` span.

object ZioOtelContextBridge {

  def tapirRequestInterceptor(storage: ContextStorage): RequestInterceptor[Task] =
    RequestInterceptor.transformResultEffect[Task](
      new RequestInterceptor.RequestResultEffectTransform[Task] {
        def apply[B](
            request: ServerRequest,
            result: Task[RequestResult[B]]
        ): Task[RequestResult[B]] = {
          // Captured while `OpenTelemetryTracing` still has the server `Span` in `Context` (synchronous transform hook).
          val ctx: Context = Context.current()
          storage.locally(ctx)(result)
        }
      }
    )
}

WDYT, is seem to works like a charm, I this is useful would you be interested by a contrib ?

Attachmenent bellow, without the Interceptor the inner span are not child of the entry point span.

Thx

Screenshot 2026-04-22 at 23.31.47
Screenshot 2026-04-22 at 23.31.472336×324 36 KB

2

Yes, that’s exactly the kind of integration that is needed to make otel work with libs like ZIO. Though, where does the context originally come from? That is - what is setting the context that’s being read by Context.current()?

3

Cool,
ThreadLocal AFAIU from opentelemetry (opentelemetry-java/context/src/main/java/io/opentelemetry/context/Context.java at main · open-telemetry/opentelemetry-java · GitHub)

4

Then @adamw do you see any issue with this interceptor ?

5

Yes, but the context needs to be populated - typically by parsing incoming tracing headers. And this has to be done by ZIO, as that’s the only component that knows about the headers :). Unless you’re setting an empty context, but then the interceptor could do just that, set an empty one?

6

You mean in case of distributed tracing (baggage & carrier) ?
My need right now was just to link tapir span and ZIO ones, distributed tracing is my next objective.

Thanks Adam.

7

Ah yes, well in the end for a full ZIO integration I think you’ll need a custom zio-tracing interceptor (instead of tapir/tracing/opentelemetry-tracing/src at master · softwaremill/tapir · GitHub which I suspect you’re using now?) so that it reads the context from ContextStorage. Plus another one for parsing the dist tracing headers.

1 Like
8

You suspicion are legit ;p

Right now I chain the 2:

ZioHttpServerOptions.customiseInterceptors
.prependInterceptor(
OpenTelemetryTracing(otel)
)
.prependInterceptor(
ZioOtelContextBridge.tapirRequestInterceptor(contextStorage)
)

AFAIU it works for me need (short term).

I will focus on implementing your solution asap.

Thanks again and good week end

1 Like
9

Hi again @adamw,

I’ve adapted the otel4s interceptor with zio-telemetry as zio-laminar-tapir/modules/server/src/main/scala/dev/cheleb/ziotapir/server/otel/ZIOpenTelemtryTracing.scala at opentelemetry-baggage · cheleb/zio-laminar-tapir · GitHub

Seems to be OK, any chance I could contribute with a tapir-otel4z-tracing module being part of Tapir ?

10

Of course :slight_smile: PRs always welcome

11

Early draft :innocent: !

But it make me realize that ZIO OpenTelemetry pulls all observability dependencies (log, tracing and metrics), hence instead of tracing/zio-tracing module is not the best name :cry:

Also, what is the best/prefered tactic to support scala 2/3 ? Stick to Scala 2 or rely on Scala2 and Scala3 sources ?