Add translation of nginx HTTP code 499?

[anuraaga]

Currently, the specs don't mention HTTP code 499 (what nginx logs when client closed the connection)

https://github.com/open-telemetry/opentelemetry-specification/blob/master/specification/trace/semantic_conventions/http.md#status

The collector currently translates it

https://github.com/open-telemetry/opentelemetry-collector/blob/master/translator/trace/grpc_http_mapper.go#L47

It's not clear whether the spec should be updated to match or the code. I would suspect the code though since 499 is a special nginx code so presumably converting that to an otel object belongs at a lower layer than our HTTP mapping?

[Oberon00]

Currently the spec maps this to InvalidArgument (other 4xx code). I think we should solve #306 before introducing more mappings. For example 410 Gone is also mapped to InvalidArgument (via other 4xx). Maybe NotFound would be better, but actually Gone means "we found this entity but have no data for it", which is different. Which goes to show that the StatusCode enum is not well-suited for HTTP.

[Oberon00]

Ah, the linked https://github.com/googleapis/googleapis/blob/master/google/rpc/code.proto#L41 on open-telemetry/opentelemetry-collector#1226 is actually interesting. So there is an official mapping from HTTP to gRPC status codes? Too bad that I didn't know of this when I wrote the mapping table.

Still, I think the best way would be to remove the StatusCode enum entirely / replace it with a better mechanism, see #306.

[anuraaga]

Thanks for this context. FWIW, I'm generally in the camp of it being fragile to map all error codes in the world to gRPC.

But I think it's good if our current code matches our current spec, and can fix forward as needed. So wondering if you can +1 this instead? open-telemetry/opentelemetry-collector#1226

[Oberon00]

For a quickfix, I think adding 499 -> Cancelled to the spec would be better, or even really referencing https://github.com/googleapis/googleapis/blob/master/google/rpc/code.proto#L32 (at some fixed revision/tag) as @james-bebbington suggested.