Configurable span attributes based on gRPC Metadata keys

[fujin]

Describe the solution you'd like
I would like to be able to specify certain gRPC Custom Metadata keys from which Span Attributes should be set on the span for the RPC.

Similar to https://opentelemetry.io/docs/instrumentation/java/automatic/agent-config/#capturing-http-request-and-response-headers

Describe alternatives you've considered

• Manually propagating the value out of the grpc metadata
• Trying something like the CustomAttributesExtractor here:

  opentelemetry-java-instrumentation/instrumentation/grpc-1.6/library/src/test/java/io/opentelemetry/instrumentation/grpc/v1_6/GrpcTest.java

  Lines 128 to 150 in aca80be

  	private static class CustomAttributesExtractor
  	implements AttributesExtractor<GrpcRequest, Status> {
  	@Override
  	public void onStart(
  	AttributesBuilder attributes, Context parentContext, GrpcRequest grpcRequest) {}
  	@Override
  	public void onEnd(
  	AttributesBuilder attributes,
  	Context context,
  	GrpcRequest grpcRequest,
  	@Nullable Status status,
  	@Nullable Throwable error) {
  	Metadata metadata = grpcRequest.getMetadata();
  	if (metadata != null && metadata.containsKey(CUSTOM_METADATA_KEY)) {
  	String value = metadata.get(CUSTOM_METADATA_KEY);
  	if (value != null) {
  	attributes.put(CUSTOM_KEY, value);
  	}
  	}
  	}

edit: Severin Neumann in the CNCF slack pointed out open-telemetry/opentelemetry-specification#2843

[Tavh]

Recently opened and started working on this issue: #6991
Isn't it pretty much the same?

[Tavh]

You're welcome to check out my PR in this subject

#7011

[fujin]

@Tavh I suppose this should be closed then?