[plugin] Add span.kind property to attribute

[OlivierAlbertini]

Here an example of span:

It would be nice to have a kind attribute for identifying if it's "server" or "client". It could be added in the zipkin/jaeger plugins. WDYT ?

[mayurkale22]

AFAIK we already set this property in each plugins and it is being properly exported in Zipkin backend (becoz it supports kind attribute). Jaeger exporter doesn;t have an equivalent mapping for kind, I was thinking to translate it into Jaeger tags similar to status.code and status.name. WDYT?

[mayurkale22]

Just checked OpenCensus' Java implementation, we have converted span.kind to Jaeger Tag. Let me know what do you think, I can open a PR to fix that.

[OlivierAlbertini]

Just checked OpenCensus' Java implementation, we have converted span.kind to Jaeger Tag. Let me know what do you think, I can open a PR to fix that.

I think that Jaeger Tag is good.

[dyladan]

Does this seem like something that should be brought up in spec? In multi-language environments it might be confusing if only some languages set the span.kind tag

[OlivierAlbertini]

Does this seem like something that should be brought up in spec? In multi-language environments it might be confusing if only some languages set the span.kind tag

I think that it depend on the backend more than the language. It's already exported in Zipkin, it's matter to be consistent. WDYT ?

it is being properly exported in Zipkin backend (becoz it supports kind attribute). Jaeger exporter doesn;t have an equivalent mapping for kind,