Tomcat instrumentation span names are not updatable from SpanProcessor

[srinusanduri]

I am trying to update span names from the SpanProcessor onStart method to redact sensitive path segments in HTTP request related span names. Span name update is working for most of auto instrumented spans except for io.opentelemetry.tomcat-7.0 library auto instrumented spans. I verified for manual instrumentation spans, kafka, grcp, spring webmvc, http-url-connection auto instrumented spans for which span name update from SpanProcessor is working fine. Below is an example trace screenshot

On further debugging, I observed that in SpanProcessor.onStart tomcat span name is received as HTTP GET which is then later updated to actual path /student before exporting somewhere after span start.

Also, I want to use tomcat span name for sampling decision. I want to drop health check requests (for example: /actuator/health), thought of using tomcat span name comparison to identify health check requests. But since tomcat span has name HTTP GET in the beginning of its lifecycle, this is not possible.

Why is tomcat span name is set as HTTP GET at start and being updated to actual path in the end? Which seems to be a deviation from all other library instrumentation spans. Its also not honoring the span name update from SpanProcessor.

[laurit]

See https://opentelemetry.io/docs/reference/specification/trace/semantic_conventions/http/ In tomcat instrumentation we are not able to determine a route so we start the span with a generic name. Later when request processing reaches a framework where we can get a route we'll update the span with a new better name. If you wish to prevent updating the span name you could try using

opentelemetry-java-instrumentation/instrumentation-api-semconv/src/main/java/io/opentelemetry/instrumentation/api/instrumenter/http/HttpRouteHolder.java

Lines 58 to 60 in b139e1d

	public static void updateHttpRoute(
	Context context, HttpRouteSource source, @Nullable String httpRoute) {
	updateHttpRoute(context, source, ConstantAdapter.INSTANCE, httpRoute);

Set the source to CONTROLLER to prevent further updates.
As in sampler you can only use the information that is available when the span is started you are better off using http.target attribute instead of the span name.