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Add a way to get the current span #101

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Add a way to get the current span #101

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6 changes: 6 additions & 0 deletions core/trace/src/main/scala/org/typelevel/otel4s/trace/Tracer.scala
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Original file line number Diff line number Diff line change
Expand Up @@ -28,6 +28,11 @@ trait Tracer[F[_]] extends TracerMacro[F] {
*/
def meta: Tracer.Meta[F]

/** Returns the span from the scope, falling back to a noop if none is
* available.
*/
def currentSpan: F[Span[F]]
Comment on lines +31 to +34
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This ship may have already sailed, but this is the signature that I think prevents using Kleisli (instead of IOLocal)

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I think that ship sailed with the Resource[F, Span[F]] that are already exposed via TracerMacro.

This is why Natchez's resource is a natural transformation: typelevel/natchez#526. I do agree we need to decide on #88 before moving forward.

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Like, is this a new API, or is it natchez-with-lazy-macros?

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this is the signature that I think prevents using Kleisli (instead of IOLocal)

So actually I'm not sure if this is true now. After getting very lost in typelevel/natchez#713 (and dragging poor @bpholt into my delusions 😅 ) I realized, isn't that PR doing exactly this? i.e. making it possible to access the Span[F] within F, without compromising a Kleisli implementation.

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I went down that same road for a while with Natchez and turned around. I had a hard time with the inner F being a Kleisli, however much I wanted the outer F to be a Kleisli, and I didn't want to introduce a G.

Note that in our case, the local environment is not a Span[F], but a (right now package-private) TraceScope.Scope.


/** Returns the context of a span when it is available in the scope.
*/
def currentSpanContext: F[Option[SpanContext]]
Expand Down Expand Up @@ -137,6 +142,7 @@ object Tracer {
private val builder = SpanBuilder.noop(noopBackend)
private val resourceUnit = Resource.unit[F]
val meta: Meta[F] = Meta.disabled
val currentSpan: F[Span[F]] = builder.startUnmanaged
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As an alternative, we can use Applicative[F].pure(Span.fromBackend(noopBackend))

val currentSpanContext: F[Option[SpanContext]] = Applicative[F].pure(None)
def rootScope: Resource[F, Unit] = resourceUnit
def noopScope: Resource[F, Unit] = resourceUnit
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8 changes: 7 additions & 1 deletion examples/src/main/scala/TracingExample.scala
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Expand Up @@ -39,7 +39,13 @@ object Work {
}

def doWorkInternal =
Console[F].println("Doin' work")
Console[F].println("Doin' work") *>
summon

def summon =
Tracer[F].currentSpan.flatMap { span =>
span.addEvent("I've been summoned.")
}
}
}

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9 changes: 9 additions & 0 deletions java/trace/src/main/scala/org/typelevel/otel4s/java/trace/TracerImpl.scala
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Expand Up @@ -21,6 +21,7 @@ import cats.effect.Sync
import cats.syntax.functor._
import io.opentelemetry.api.trace.{Span => JSpan}
import io.opentelemetry.api.trace.{Tracer => JTracer}
import org.typelevel.otel4s.trace.Span
import org.typelevel.otel4s.trace.SpanBuilder
import org.typelevel.otel4s.trace.SpanContext
import org.typelevel.otel4s.trace.Tracer
Expand All @@ -33,6 +34,14 @@ private[java] class TracerImpl[F[_]: Sync](
val meta: Tracer.Meta[F] =
Tracer.Meta.enabled

def currentSpan: F[Span[F]] =
scope.current.map {
case TraceScope.Scope.Span(_, jSpan, ctx) =>
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Should we check that the context is also valid if ctx.isValid?

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Yes, I think so.

Span.fromBackend(new SpanBackendImpl(jSpan, ctx))
case TraceScope.Scope.Noop | TraceScope.Scope.Root(_) =>
Span.fromBackend(Span.Backend.noop)
}

def currentSpanContext: F[Option[SpanContext]] =
scope.current.map {
case TraceScope.Scope.Span(_, _, spanCtx) if spanCtx.isValid =>
Expand Down