[exporter/pkg/translator/prometheus] colon in metric names is being replaced with underscore, even when featureGate is used

[premendrasingh]

Is your feature request related to a problem? Please describe.

When following metrics are harvested, leading colon is removed and rest of the colons are replaced with underscore.
Using feature flag pkg.translator.prometheus.NormalizeName I was expecting to retain the colons.

Prometheus allows these metrics to be harvested and does not changes the metric name. Check attached screenshot of Prometheus showing metrics with colon.

# HELP foobar with colon
# TYPE foobar counter
:foo::bar_total 7736

Describe the solution you'd like

Fix behavior of featureGate ** pkg.translator.prometheus.NormalizeName** to allow colons in metric names so that behavior is same as Prometheus client.

Describe alternatives you've considered

Add another featureGate to translator to allow colon in metric names.
pkg.translator.prometheus.AllowColonInMetricNames

Additional context

No response

[bogdandrutu]

Where is the name format for Prometheus?

[premendrasingh]

Metric name format taken from -

https://prometheus.io/docs/concepts/data_model/#metric-names-and-labels

The metric name specifies the general feature of a system that is measured (e.g. http_requests_total - the total number of HTTP requests received). It may contain ASCII letters and digits, as well as underscores and colons. It must match the regex [a-zA-Z_:][a-zA-Z0-9_:]*

[vjsamuel]

thank you @bogdandrutu and @Aneurysm9 for comments on slack. Per https://github.com/OpenObservability/OpenMetrics/blob/main/specification/OpenMetrics.md#text-format it is safe to assume that : can be a first character and a character after that.

metricname = metricname-initial-char 0*metricname-char

metricname-char = metricname-initial-char / DIGIT
metricname-initial-char = ALPHA / "_" / ":"

that being said, we can file a fix for the same. @premendrasingh @newly12 can one of you please file a PR to address this?