Automatic URLSessionTaskMetrics performance tracking?

[WFT]

Does Sentry support gathering URLSessionTaskTransactionMetrics with its automatic URLSession breadcrumbs/performance tracking? If so, how do I enable it? As far as I can tell the default options don't do it.

It would be helpful to track the performance of our API from the perspective of our end users to know at least:

• “secure connection time” AKA tls time
• fetchStartDate -> responseStartDate AKA “time to first byte”

[philipphofmann]

No, we don't support that feature at the moment. The URLSessionTaskMetrics works by using a delegate with something like the following

guard let imgUrl = URL(string: "https://sentry-brand.storage.googleapis.com/sentry-logo-black.png") else {
    return
}
let session = URLSession(configuration: URLSessionConfiguration.default)
let dataTask = session.dataTask(with: imgUrl) { (_, _, _) in }
dataTask.delegate = Delegate()
dataTask.resume()

class Delegate: NSObject, URLSessionTaskDelegate {
    func urlSession(_ session: URLSession, task: URLSessionTask, didFinishCollecting metrics: URLSessionTaskMetrics) {

    }
}

Our NetworkTracking integration swizzles the NSURLSessionTask setState and resume methods.

sentry-cocoa/Sources/Sentry/SentryNetworkTrackingIntegration.m

Lines 57 to 62 in 4386045

	+ (void)swizzleURLSessionTask
	{
	NSArray<Class> *classesToSwizzle = [SentryNSURLSessionTaskSearch urlSessionTaskClassesToTrack];
	SEL setStateSelector = NSSelectorFromString(@"setState:");
	SEL resumeSelector = NSSelectorFromString(@"resume");

As we have to use a delegate to retrieve the URLSessionTaskMetrics, we can't simply set our delegate as we could overwrite existing delegates. Maybe we could set our own delegate and forward requests to the existing delegate, but that sounds a bit hacky. What are your thoughts, @brustolin?

[WFT]

Hey, thanks for responding! That makes sense — it is a little hairy if you’re not already intercepting delegate messages.

Maybe a good place to start would be a method that lets end users who have a delegate already report this info to Sentry?

Something like SentrySDK.reportURLSessionTaskMetrics(session, task, metrics) which does the necessary work of pulling out the spanId/traceId, adding all the child spans and their measurements/data. Then end users of the library could create their own delegates which call that.

[philipphofmann]

Yes, we could do what you suggested, but the downside is that you still have to do some manual work, and we always try to give you as much as we can out of the box.

[philipphofmann]

@WFT, we created an issue for adding a manual API #3180. We can't give you an ETA yet.

[WFT]

Thanks @philipphofmann ! I've already created my own solution for my codebase, so I'm not too worried about the ETA; I just think it would be a good thing for everyone to have!

[brustolin]

Maybe we could set our own delegate and forward requests to the existing delegate

I don't like this solution either, it is a little bit dangerous.
The manual api would be the easiest solution right now. But not the friendliest for the user.