Add the ability to safely get the root span from the tracer

[alexrhogue]

It would be very helpful to be able to get the root span of a request safely from the tracer object via a public function/getter. Currently to do this I need to use a private property (code provided by @rochdev):

// anywhere during the request lifecycle
const span = tracer.scope().active()

if (span) {
  const rootSpan = span.context()._trace.started[0];
}

I propose something like the following:

tracer.scope().rootSpan();
//or
tracer.scope().active().rootSpan();

This would make it much easier to add tags and information to the root of a request without having to communicate via the req object and/or plugin hooks.

[rochdev]

This is unfortunately not something we can support since it would break for asynchronous workflows. I will close this for now, but please feel free to re-open if you have a use case where using span hooks doesn't work.

[mintuhouse]

I want to addTags to localRootSpan (similar to https://docs.datadoghq.com/tracing/setup_overview/custom_instrumentation/java/#set-tags--errors-on-a-root-span-from-a-child-span in java)

I don't have access to express req at the point where I am adding these tags. Is there a way to addTags on localRootSpan?

[rochdev]

@mintuhouse Unfortunately there is no official way right now. You can grab the root on the span context of any span within a trace with span.context()._trace.started[0] but that is a private API that might change.

[rkrv]

Hi folks, just chiming in about our use case. We are using Next.js and adding an owner tag on the entry span to route errors to appropriate teams that maintain those pages. Hooks are not enough in this case, as the owner metadata lives together with the source code for the Next.js page. Any suggestions for implementation besides using the span.context()._trace.started[0] snippet?

[TREFZ]

if you have a use case where using span hooks doesn't work

I'm trying to do the same as the OP, add tags to the root span. But I'm unfamiliar with span hooks, so it's possible that would work for my use case. Can someone direct me to docs on span hooks, or an example of how that would work?

EDIT: I found it.