Add http client url template customizer

[laurit]

Add an SPI for customizing http client url.template attribute and the http client span name that is computed from it. This PR also includes a regular expression based customizer that allows for matching the http client url agains regular expressions to produce url templates. It can be configured by setting otel.instrumentation.http.client.url-template-rules to a semicolon separated string consisting of replacement rules where each rule is a comma separated triplet of regex pattern used to match url, replacement, whether this rule can override existing url template (optional parameter). Url template is computed via pattern.matcher(url).replaceFirst(replacement) so replacement can contain capture groups used in the pattern. Note that since url templates are experimental otel.instrumentation.http.client.emit-experimental-telemetry also needs to be set.

[zeitlinger]

This PR does not implement declarative config.

Declarative config is ready to be used, so we should support declarative config only - similar to how you have to use declarative config for more advanced method config

[zeitlinger]

I'm wondering how this customizer is/should be related to the recently added InstrumenterCustomizer. They are closely related, so maybe InstrumenterCustomizer can just be extended.

[laurit]

I'm wondering how this customizer is/should be related to the recently added InstrumenterCustomizer. They are closely related, so maybe InstrumenterCustomizer can just be extended.

I don't know how to implement this on top of InstrumenterCustomizer as it is.

[laurit]

This PR does not implement declarative config.

Declarative config is ready to be used, so we should support declarative config only - similar to how you have to use declarative config for more advanced method config

implemented

[zeitlinger]

I'm wondering how this customizer is/should be related to the recently added InstrumenterCustomizer. They are closely related, so maybe InstrumenterCustomizer can just be extended.

I don't know how to implement this on top of InstrumenterCustomizer as it is.

something like customizer.addAttributesExtractor(HttpExperimentalAttributesExtractor.createWithHttpClientUrlTemplateCustomizer(..))

but that's not thought through

[zeitlinger]

I wonder what the right place to document this is, in particular the declarative config syntax. Maybe a javadoc or README?

[laurit]

something like customizer.addAttributesExtractor(HttpExperimentalAttributesExtractor.createWithHttpClientUrlTemplateCustomizer(..))

but that's not thought through

The first hurdle is that you need to somehow tell which instrumenters are for http clients, incidentally I was planning to implement something for it. Assuming you can do it then you'd need some way to detect whether this attribute is already set. This can be done by calling build on the AttributesBuilder or relying on the internal workings of UnsafeAttributes. After that you'd need to somehow also influence the span naming which is tricky because here you also need to tell whether the original name already had the template appended which. I think the current solution is simpler.