Adding a tag to the ASP.NET Request Activity

Question

I would like to add a tag to the System.Diagnostics.Activity object for each incoming ASP.NET Request, as soon as the request-handling starts. Is there a way I can access the ActivitySource for the Request Pipeline, and add a listener to it?

Currently I'm thinking of using a Pipeline middleware, but there has to be a more lightweight way. Especially one where other developers can't add any other middleware handlers before this one. Any ideas?

Answer 1

Looks like you can add it via DI at startup. The Key thing is the name of the ActivitySource. I couldn't find it in any documentation. I had to trawl through the aspnetcore code, and it looks like registers an empty name ActivitySource for the DiagnosticListener.

In any case ...

Add the following to Configure(...):

var requestActivityListener= new ActivityListener();
requestActivityListener.ShouldListenTo = activitySource => activitySource.Name == "";
requestActivityListener.ActivityStarted = activity => LetsShapeThisActivityToOurLiking(activity);
ActivitySource.AddActivityListener(requestActivityListener);

That should be it.