OtelToZipkinSpanTransformer does not attach ResourceAttributes

[jonatan-ivanov]

Describe the bug
If I use the Jaeger Exporter, I see the following resource attributes on spans:

telemetry.sdk.language
telemetry.sdk.name
telemetry.sdk.version

But if I use the Zipkin Exporter, these resource attributes are missing. I think this is because
OtelToZipkinSpanTransformer does not add them to the span as tags. According to the docs these values are mandatory for the SDK so I think the Zipkin Exporter should not just drop them.

Steps to reproduce
Send some spans using the Zipkin Exporter.

What did you expect to see?
The mandatory resource attributes should be added to Zipkin spans as tags.

What did you see instead?
Those tags are missing.

What version and what artifacts are you using?
Artifacts: opentelemetry-sdk, opentelemetry-exporter-zipkin
Version: 1.27.0
How did you reference these artifacts?

implementation 'io.opentelemetry:opentelemetry-exporter-zipkin'

Environment
Java: liberica-17.0.7+7

❯ java --version
openjdk 17.0.7 2023-04-18 LTS
OpenJDK Runtime Environment (build 17.0.7+7-LTS)
OpenJDK 64-Bit Server VM (build 17.0.7+7-LTS, mixed mode, sharing)

OS: Mac OS 13.4.1

Additional context
N/A

[jkwatson]

Currently, it's not specced what to do with resource attributes in zipkin: https://github.com/open-telemetry/opentelemetry-specification/blob/main/specification/trace/sdk_exporters/zipkin.md

[jonatan-ivanov]

Shouldn't it tough? I would assume this hasn't been specced yet but since the spec you linked seems stable, I'm questioning this assumption. Are there intentions to fix this?

Since the docs are saying that these values are mandatory for the SDK, I think the Zipkin Exporter should not drop them.

[jack-berg]

There's a spec issue tracking this but it hasn't received much attention / feedback. I'd support an effort to help resolve this at the spec level.

[jack-berg]

Realized this is a duplicate of #3009.