W3C context propagation does not properly create local context from received traceparent header

[pnerg]

Issue

When creating the local context using the header traceparent the local spanID is incorrectly using the received traceID.

Steps to reproduce

Enable w3c propagation

 #configure W3C context propagation
  kamon.propagation.http.default.entries {
    incoming.span = "w3c"
    outgoing.span = "w3c"
  }

Run simple app

import akka.actor.ActorSystem
import akka.http.scaladsl.Http
import akka.http.scaladsl.server.Directives._
import akka.stream.ActorMaterializer
import com.typesafe.config.ConfigFactory
import kamon.Kamon
import org.slf4j.LoggerFactory

object Server extends App {
  Kamon.init(ConfigFactory
    .defaultApplication()
    .withFallback(ConfigFactory.defaultOverrides())
    .withFallback(ConfigFactory.defaultReference())
    .resolve()
  )
  private implicit val system = ActorSystem("simple-kamon-server")
  private implicit val materializer = ActorMaterializer()
  private implicit val executionContext = system.dispatcher
  private val logger = LoggerFactory.getLogger(Server.getClass)
  val route = pathPrefix("api" / "account" / Segment / "details") { id =>
    val span = Kamon.currentSpan()
   logger.info(s"Got request for account details with id [$id] using TraceID [${span.trace.id.string}], SpanID [${span.id.string}] parentSpan [${span.parentId.string}] and sampled [${span.trace.samplingDecision}]")
   complete("OK")
 }

  Http()
    .newServerAt("0.0.0.0", 9696)
    .bindFlow(route)
    .map(_.localAddress)
    .map{addr =>
      val port = addr.getPort
      logger.info(s"Started on port $port")
    }
}

Send request with w3c header

http://localhost:9696/api/account/1234/details
traceparent: 00-0af7651916cd43dd8448eb211c80319c-b7ad6b7169203331-01

The printout from the app is

Got request for account details with id [1234] using TraceID [0af7651916cd43dd8448eb211c80319c], SpanID [0af7651916cd43dd8448eb211c80319c] parentSpan [b7ad6b7169203331] and sampled [sample]

As one can see the traceID and spanID are equal, which they of course should not be.

Reason

Looking at the code where the context is created (snippet below)

   if (traceParentComponents.length != 4) None else {
      val traceID = identityProvider.traceIdFactory.from(traceParentComponents(1))
      val spanID = identityProvider.spanIdFactory.from(traceParentComponents(2))
      val samplingDecision = unpackSamplingDecision(traceParentComponents(3))

      Some(Span.Remote(traceID, spanID, Trace(traceID, samplingDecision)))
    }

https://github.com/kamon-io/Kamon/blob/master/core/kamon-core/src/main/scala/kamon/trace/SpanPropagation.scala#L97
The Span.Remote is not correct, it is using the traceID as the new spanID.
Since W3C only propagates the parent context it means a new spanId needs to be generated and added to the context.

[pnerg]

ping @duxet, the nasty tester is at it again...:)

[SimunKaracic]

Do you two have this under control, or should I spend some time on it? :D

[pnerg]

@SimunKaracic I don't have a recent fork of Kamon so I assume it's much faster for you to fix it.
Should pretty much only be to generate a 8-byte identifier for the local span.

[duxet]

@pnerg Thanks! Your issue description is a piece of really good work :D

I've opened PR #978 with a quick fix.

[pnerg]

Thx, I really hate the typical issue ticket..."nnn doesn't work" without any description nor analysis
In fact I tend to reject tickets without a description on how to reproduce it

[SimunKaracic]

Fixed in 2.1.15!
Thanks for the nice report and quick fix 🎉