[instrumentation-undici] Traceparent not propagated correctly when header already exist in the request

[hectorhdzg]

What version of OpenTelemetry are you using?

"@opentelemetry/sdk-node": "^0.200.0"

What version of Node are you using?

18.17.0

What did you do?

Enable undici instrumentation, manually add traceparent to request, make request using fetch

What did you expect to see?

traceparent header is propagated correctly

What did you see instead?

Incorrect format of traceparent causing parseTraceParent in W3CTraceContextPropagator to fail and return null

Ex:
traceparent = "00-5c4f0bdefa3390bbb38cc02bc2766517-7104f40181c58265-01, 00-5c4f0bdefa3390bbb38cc02bc2766517-db1f1457d0e19314-01"

Additional context

Related to
open-telemetry/opentelemetry-js#5590

[dyladan]

I took a look at this and there's not an easy way to solve this. I think this requires some specification in order to extend the propagation interface with a shouldInject or similar function.

Add a setter that checks for header existence

If the traceparent already exists but tracestate does not, then tracestate would be injected. This is not what we want because then we're mixing tracing systems in a single request which would be bad.

Propagator checks if headers already exists

There's no way to implement this because there isn't a textmap of existing headers already from undici, and inject doesn't have a getter anyway, only a setter.

[pichlermarc]

@dyladan opened a Spec issue regarding this: open-telemetry/opentelemetry-specification#4496