This PR addresses a memory leak issue in the OpenTelemetry tracing middleware.

The existing middleware invokes NewHandler for each incoming request, which results in the allocation of a new oteltracehttp.Handler.

func TraceHandler(h http.Handler, opts ...otelhttp.Option) http.Handler {
	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
		NewHandler(h, r.URL.Path, opts...).ServeHTTP(w, r)
	})
}

In our setup, this led to an increase of over 300MB per day per Hydra instance in allocated memory. Similar observations have been reported in open-telemetry/opentelemetry-go-contrib#2413.

This PR modifies the middleware to utilize a SpanNameFormatter function instead of passing the path to NewHandler. This preserves the existing functionality while eliminating the memory leak.

Related Issue or Design Document

The issue has been reported in projects using the library (e.g., ory/hydra#3495).

Checklist

• I have read the contributing guidelines and signed the CLA.
• I have referenced an issue containing the design document if my change introduces a new feature.
• I have read the security policy.
• I confirm that this pull request does not address a security vulnerability.
  If this pull request addresses a security vulnerability,
  I confirm that I got approval (please contact [email protected]) from the maintainers to push the changes.
• I have added tests that prove my fix is effective or that my feature works.
• I have added the necessary documentation within the code base (if appropriate).

Further comments

• The otelhttptrace applies the passed options in sequential order. We prepend the SpanNameFormatter to allow users to override the SpanNameHandler if needed.