Update span status & description setting to comply with the spec

[matej-g]

Related PRs (merged ones ticked off)

• Jaeger Exporter: Fix minor mapping discrepancies Jaeger Exporter: Fix minor mapping discrepancies #1626
• Zipkin Exporter: Adjust span transformation to comply with the spec Zipkin Exporter: Adjust span transformation to comply with the spec #1688
• Span status from HTTP code: Do not set status message if it can be inferred Span status from HTTP code: Do not set status message if it can be inferred #1681

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According to recent spec change in open-telemetry/opentelemetry-specification#1186 and
open-telemetry/opentelemetry-specification#1257:

Regarding exporters

For Jaeger status code and message (excerpts):

Span Status MUST be reported as a key-value pair in tags to Jaeger, unless it is UNSET.
In the latter case it MUST NOT be reported.

|Code | otel.status_code | Name of the code, either OK or ERROR. MUST NOT be set if the code is UNSET. |
|Description | otel.status_description | Description of the Status if it has a value otherwise not set. |

For Zipkin status code and description (excerpts):

|Description| error | Description of the Status. MUST be set if the code is ERROR, use an empty string if Description has no value. MUST NOT be set for OK and UNSET codes. |

Regarding status from HTTP status code (open question)

Furthermore, the spec now states that:

Description MUST be IGNORED for StatusCode Ok & Unset values.

and in HTTP semantic conventions spec:

Don't set the span status description if the reason can be inferred from http.status_code.

Generally this seems to be the case, however SpanStatusFromHTTPStatusCode, which - although not returning directly span status with description - is returning accompanying message for all statuses. The question is whether this acceptable (and the burden of checking and (not) setting span status is on the caller of SpanStatusFromHTTPStatusCode) or this could be simplified to return empty string for success statuses.

[matej-g]

@MrAlias I updated the description as there was another related change to the spec (see the update description), I think it makes sense to tackle it all in one go. I hope the update is OK, not sure whether it changes priority etc.

Also happy to pick up this issue ⬆️

[matej-g]

Hello @MrAlias! I've been looking into this and I think there are even more (although mostly minor) discrepancies between the exporters and the spec, since I opened this. I think I will split the changes into separate PRs, one for each exporter, for better review process, just FYI.

[MrAlias]

@matej-g sounds good 👍

[MrAlias]

Adding the following tasks to this to be explicit for what we need in the Jaeger exporter:

• The status code tag needs to be renamed from "status.code" to "otel.status_code"
• The status description tag needs to be renamed from "status.message" to "otel.status_description"
• The status description tag needs to not be set if the status message is not set.

It might be worth splitting this issue into smaller ones.

[MrAlias]

Addressing that last comment in #1761