Update prom client with support for UTF-8

[zeitlinger]

To avoid a breaking change

• a new flag has been introduced to opt-in to UTF-8 support: otel.exporter.prometheus.utf8 -> this is wrong
• we should use translation_strategy instead
  • see Prometheus translation with UTF-8 and __ opentelemetry-specification#4634
  • requires add option to disable metric suffixes prometheus/client_java#1557

[codecov]

Codecov Report

❌ Patch coverage is 94.73684% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 89.98%. Comparing base (63d4617) to head (4c214e3).
⚠️ Report is 2 commits behind head on main.

Files with missing lines	Patch %	Lines
...ry/exporter/prometheus/PrometheusMetricReader.java	66.66%	1 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##               main    #7588      +/-   ##
============================================
- Coverage     89.99%   89.98%   -0.01%     
- Complexity     7079     7081       +2     
============================================
  Files           803      803              
  Lines         21412    21428      +16     
  Branches       2086     2087       +1     
============================================
+ Hits          19269    19282      +13     
- Misses         1479     1482       +3     
  Partials        664      664              

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[zeitlinger]

@jkwatson please have a look

[jkwatson]

Is this the official property? I thought no new properties were being added to the spec?

[zeitlinger]

See #7588 (comment)

[jkwatson]

That doesn't answer my question... if we're adding new configuration properties, I'd like to make sure they're "official" in the spec, and we're not going off on our own, especially as there has been a moratorium set on the new configuration properties/env vars in the spec (at least, the last I heard).

[zeitlinger]

Got it 😄

This is the part in the Go SDK: https://github.com/open-telemetry/opentelemetry-go/blob/d0cab8666b740c975f028236610cab2663f02031/exporters/prometheus/config.go#L44-L66

@ArthurSens it seems there is no env var to set the translation strategy - is that missing?

[zeitlinger]

got the answer: it should be translation_strategy instead: https://github.com/open-telemetry/opentelemetry-specification/blob/main/specification/metrics/sdk_exporters/prometheus.md#configuration

[jkwatson]

why did these keys change, when we haven't explicitly changed the exporter?

[zeitlinger]

I set UTF-8 to true in most tests - including here

[jkwatson]

no longer blocked by the spec?

[zeitlinger]

no longer blocked by the spec?

We talked in the spec meeting that it's up to the SDKs to decide if __ should be converted to _ or not.

So from that point of view, we're free to keep __ as is.
However, I didn't want to introduce a breaking change (which is also SDK decision) - so I added a setting to enable UTF-8.

If

• otel.exporter.prometheus.utf8 is false, we shorten __ to _ (and %% becomes __ and then _)
• otel.exporter.prometheus.utf8 is true, the SDK passes all chars as is to the prom client - expecting that the user wants to keep that as is in the entire pipeline

We can decide that we're OK with the breaking change - and then we don't need this property.