Add url.template attribute to otel4s-metrics-backend

[remimomprive]

Implementing the experimental attribute url.template for the metric http.client.request.duration
See https://opentelemetry.io/docs/specs/semconv/http/http-metrics/#metric-httpclientrequestduration

Before submitting pull request:

• Check if the project compiles by running sbt compile
• Verify docs compilation by running sbt compileDocs
• Check if tests pass by running sbt test
• Format code by running sbt scalafmt

[Copilot]

Pull request overview

Adds support for the experimental url.template semantic attribute in the otel4s-metrics-backend, aligning emitted attributes with the experimental OpenTelemetry HTTP client metrics semconv.

Changes:

• Emit url.template (experimental) on metrics attributes via a simple URI templating heuristic.
• Update semantic test to use HttpExperimentalMetrics.ClientRequestDuration.
• Add otel4s-semconv-experimental dependency required for the new attribute.

Reviewed changes

Copilot reviewed 2 out of 3 changed files in this pull request and generated 2 comments.

File	Description
observability/otel4s-metrics-backend/src/main/scala/sttp/client4/opentelemetry/otel4s/Otel4sMetricsBackend.scala	Adds url.template attribute emission and URI templating helper.
observability/otel4s-metrics-backend/src/test/scala/sttp/client4/opentelemetry/otel4s/Otel4sMetricsBackendTest.scala	Switches duration metric semantic spec to experimental variant.
build.sbt	Adds otel4s-semconv-experimental dependency for main compilation.

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[Copilot]

urlTemplate currently includes query parameter values in the emitted url.template (e.g., k=v is kept when v doesn't match IdRegex). Query values commonly contain tokens/PII and can also explode metric cardinality. Consider omitting the query string from url.template entirely, or at minimum templating all query values (e.g., k={value}) so no raw values are exported.

Suggested change

	case Uri.QuerySegment.KeyValue(k, v, _, _) =>
	s"$k=${if (IdRegex.matches(v)) IdPlaceholder else v}"
	case Uri.QuerySegment.Value(v, _) =>
	if (IdRegex.matches(v)) IdPlaceholder else v
	case Uri.QuerySegment.Plain(v, _) =>
	IdRegex.replaceAllIn(v, IdPlaceholder)
	case Uri.QuerySegment.KeyValue(k, _, _, _) =>
	s"$k={value}"
	case Uri.QuerySegment.Value(_, _) =>
	"{value}"
	case Uri.QuerySegment.Plain(_, _) =>
	"{value}"

[Copilot]

The new urlTemplate logic is non-trivial (path+query templating, change detection) but the existing semantic test only asserts required attributes and may not fail if url.template is missing/incorrect. Add a focused test case that sends a request with an ID-like path/query (e.g., /users/123?token=...) and asserts the recorded metric attributes include url.template with the expected placeholders.

[adamw]

As I understand, the PR includes a heuristic to determine what's the template. Can you describe the heuristic? Why do you think it would work in a generic setting?

[remimomprive]

As I understand, the PR includes a heuristic to determine what's the template. Can you describe the heuristic?

It replaces all the magic numbers and UUIDs from both the path parameters and query parameters with {id}

Why do you think it would work in a generic setting?

It works for the examples from the spec (https://opentelemetry.io/docs/specs/semconv/registry/attributes/url/#url-template). If that's too specific, we can add a default implementation in Otel4sMetricsConfig and let the user chose the implementation

[adamw]

Thanks I see :) I think that the URLs in the wild might be very varied. Maybe we can have this as an optional feature, activated by the config? And in the config, we could have a function Uri => Option[String] or sth like this, which would return the template. One out-of-the-box implementation of the function could be what you have in code now, just not activated by default. Some docs around this would be great to have as well.

[remimomprive]

Sure! I'll rework that to apply the comments