Getting the http.route to be sent in headers to downstream calls.

[ananthcodekarma]

Hi,

I am trying to build a service graph and I would like to send some data based on the 'http.route' attribute in the call. The flow works like this.

Java 8+ on SpringBoot 2.5+

Step 1: Read the 'X-Custom-Header' value from the input request header and save it in the context. If the header is not present, just assume it to be empty.
Step 2: Get the http.route value from the span. This tell the Controller's path that was invoked as a part of the request.
Step 3: Create a new header which takes in the X-Custom-Header read in the input and the http.route of the span attribute and pass it as a new X-Custom-Header in any downstream calls.

This is done in every service in the service graph.

1. I tried using the TextMapPropagator interface. I was able to extract the header value in the extract function.
2. I want to read the http.route attribute in the inject method and create a custom header out of it.

Now the question.

I am finding no way to access the http.route attribute in the SpanContext. I tried a SpanProcessor but the value is not set till the Span is ended. Unfortunately, all the downstream calls made as a part of serving a request in SpringBoot. So the ControllerSpan is not ended while the Service is read.

I can write a custom agent to extract this value and somehow either store in otem Context of Baggage. But I am thinking if there is a way to do it by an Otem Agent Extension itself.

Thanks,