How to subscribe to ExceptionRecorder

[jamescrosswell]

In net9.0 and later, the ActivityListener class has an ExceptionRecorder property that can be used to register one or more callbacks that will be called when an Exception occurs:

        /// <summary>
        /// Set or get the callback used to listen to <see cref="Activity"/> events when exceptions are added.
        /// </summary>
        public ExceptionRecorder? ExceptionRecorder { get; set; }

Is there any way to register a callback on the activity listeners for sources that have been added to the TracerProviderBuilder?

[cijothomas]

Only if you directly setup ActivityListener yourself. OTel SDK does this underneath, but does not expose anything in OTel itself to react to this.

[jamescrosswell]

Thanks @cijothomas - I did experiment with that approach (here).

However, without knowing which sources OpenTelemetry is configured to listen to, the only way to make it work is by listening to everything:

new ActivityListener
        {
            ShouldListenTo = _ => true,
            ExceptionRecorder = OnExceptionRecorded
        };

Everything is a really big set of information in the context of an enterprise application with distributed tracing... so I don't think that's a practical solution to the problem (it's an interesting experiment, but I can't put it in production).

[cijothomas]

Nice!
If interested, there are lot of discussions in the spec about where to attach exceptions to - to Span(Activity) or Events/Logs... open-telemetry/opentelemetry-specification#4333

[jamescrosswell]

I'll see if I can resurrect that pr/discussion as it looks like it was closed as stale.

It looks like long term the plan is to stop people from recording/adding exceptions via Traces... which would be fine, except that there are already/still APIs like Activity.AddException in use today. While we still have those methods, we need some way to deal with the data they capture.