prometheusreceiver: Append.*CTZeroSample methods don't covert milliseconds to seconds

[ridwanmsharif]

Component(s)

receiver/prometheus

What happened?

Description

When being called Append.*CTZeroSample is called with ctMs in milliseconds.

This inturn calls addCreationTimestamp in milliseconds. But that assumes and sets mg.created as though it is called with seconds.

This causes the resulting metrics to have wildly incorrect start times when it is set here:

opentelemetry-collector-contrib/receiver/prometheusreceiver/internal/metricfamily.go

Line 147 in d1f343c

point.SetStartTimestamp(timestampFromFloat64(mg.created))

since no conversion is done.

This was introduced in this PR: #36660

And this bug was present ever since.

Steps to Reproduce

scrape metrics that have the _created metrics and see if the start time is set appropriately when converted to OTLP

Steps to fix

I'll be sending a PR that makes sure that when mg.created is set, it is set in seconds as expected here: https://github.com/prometheus/OpenMetrics/blob/main/specification/OpenMetrics.md#counter

Collector version

0.120.0 to latest

Environment information

Environment

OS: (e.g., "Ubuntu 20.04")
Compiler(if manually compiled): (e.g., "go 14.2")

OpenTelemetry Collector configuration

Log output

Additional context

No response

[github-actions]

Pinging code owners:

• receiver/prometheus: @Aneurysm9 @dashpole @ArthurSens @krajorama

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[ArthurSens]

Nice find!

[ridwanmsharif]

When trying to hunt this bug down there were other things I noticed. We also look for the _created metrics in the receiver:

opentelemetry-collector-contrib/receiver/prometheusreceiver/internal/metricfamily.go

Lines 400 to 401 in edb75a5

	case metricName == mf.metadata.Metric+metricSuffixCreated:
	mg.created = v

and try to update the timestamp there as well (in addition to the Append.*CTZeroSample call which I think achieves the same thing already?)

If I'm right, we can remove and clean some of that up now that Append.*CTZeroSample is fully implemented. Is my understanding correct here? Happy to help with some clean up too :)