URLSessionInstrumentation doesn't call the urlSession(_:dataTask:didReceive:) method

[ddas09]

Description:
I am encountering an issue where the URLSessionInstrumentation fails to swizzle the urlSession(_:dataTask:didReceive:) method in a custom delegate class. While the instrumentation works for other delegate methods like urlSession(_:task:didFinishCollecting:), it does not intercept the urlSession(_:dataTask:didReceive:) method.

Here is my code -

public class CustomSessionDelegate: NSObject, URLSessionDataDelegate, URLSessionTaskDelegate {
    public func urlSession(_ session: URLSession, dataTask: URLSessionDataTask, didReceive data: Data) {
        print("Data received")
    }
}

let delegate = CustomSessionDelegate()
let session = URLSession(configuration: .default, delegate: delegate, delegateQueue: nil)

let networkInstrumentation = URLSessionInstrumentation(
    configuration: URLSessionInstrumentationConfiguration(
        delegateClassesToInstrument: [CustomSessionDelegate.self]
    )
)

Expected Behavior:
The injectTaskDidReceiveDataIntoDelegateClass method should find the urlSession(_:dataTask:didReceive:) method in the delegate class and swizzle it for instrumentation.

More Info
When debugging, I saw the code never goes into this and skips this block (not sure though why) -

let block:
      @convention(block) (Any, URLSession, URLSessionTask, URLSessionTaskMetrics) -> Void = { object, session, task, metrics in
        if objc_getAssociatedObject(session, &idKey) == nil {
          self.urlSession(session, task: task, didFinishCollecting: metrics)
        }
        let key = String(selector.hashValue)
        objc_setAssociatedObject(session, key, true, .OBJC_ASSOCIATION_RETAIN_NONATOMIC)
        let castedIMP = unsafeBitCast(originalIMP,
                                      to: (@convention(c) (Any, Selector, URLSession, URLSessionTask, URLSessionTaskMetrics) -> Void).self)
        castedIMP(object, selector, session, task, metrics)
        objc_setAssociatedObject(session, key, nil, .OBJC_ASSOCIATION_RETAIN_NONATOMIC)
      }

Note: urlSession(_:task:didFinishCollecting:) - this method seems to work fine though with the same instrumentation.

It's been a blocker for us!

[ddas09]

@nachoBonafonte / @bryce-b, I feel this is related to this issue

[ddas09]

Update on this -

After some debugging, I saw it does swizzle the urlSession(_:dataTask:didReceive:) method. But when request is made, the swizzled block never gets called -

let block:
      @convention(block) (Any, URLSession, URLSessionTask, URLSessionTaskMetrics) -> Void = { object, session, task, metrics in
        if objc_getAssociatedObject(session, &idKey) == nil {
          self.urlSession(session, task: task, didFinishCollecting: metrics)
        }
        let key = String(selector.hashValue)
        objc_setAssociatedObject(session, key, true, .OBJC_ASSOCIATION_RETAIN_NONATOMIC)
        let castedIMP = unsafeBitCast(originalIMP,
                                      to: (@convention(c) (Any, Selector, URLSession, URLSessionTask, URLSessionTaskMetrics) -> Void).self)
        castedIMP(object, selector, session, task, metrics)
        objc_setAssociatedObject(session, key, nil, .OBJC_ASSOCIATION_RETAIN_NONATOMIC)
      }

Also, I see this is not the case for the Network Instrumentation example here. In the network sample, the block is executed fine.

I was seeing the issue when I am testing a sample iOS 18.2 app.

[ddas09]

Update 2:

I see if we use a completion handler-based URLSession API (like dataTask(with:completionHandler:)), the URLSessionDelegate methods are not called.

let task = session.dataTask(with: requestUrl) { data, response, error in
            self.handleResponse(data: data, response: response, error: error, completion: completion)
 }

The delegate methods are only triggered when using a session created with a delegate, and when using the delegate-based API, i.e., dataTask(with:) without a completion handler -

let task = session.dataTask(with: request) // without any handler

I see after this change, the didRecieve:data is being called. But I want to know if there is a more efficient way to handle this scenario. As the CustomSessionDelegate will be passed by the users and we can't rely on that.

[bryce-b]

@ddas09 This may be an issue with your order of operations. You may need to initialized the instrumentation before creating your URLSession. Can you give that a try?

[ddas09]

@bryce-b, thanks for replying. I am currently initialising the instrumentation before creating the URLSession object only. It seems like the issue only occurs when we use a completion handler-based URLSession API (like dataTask(with:completionHandler:)).

See my previous comment for more details .

Update 2:
I see if we use a completion handler-based URLSession API (like dataTask(with:completionHandler:)), the URLSessionDelegate methods are not called.

[nachoBonafonte]

Can you provide a sample app that reproduces the issue? Are you using any other SDK in the same app that also does swizzling?

[ddas09]

@nachoBonafonte, I made the same changes in the Network Sample file - ddas09@ee95785

You can observer with this changes, the delegates didRecieve:data method is not being called. However, if you uncomment the commented code in the simpleNetworkCallWithDelegateAndCompletionHandler and the delegate method, you would notice the delegate method gets called.

Hope this will help. Let me know if you need any further info.

cc: @bryce-b

[ddas09]

@nachoBonafonte, did you get a chance to look into it further?

[nachoBonafonte]

Yes, I think it might by a system limitation, where it decides not to call the delegate methods even when documented as such, it started with async network requests, where only a pair of delegate methods were really called, it may have expanded to other siyuations. Have you tested with previous iOS versions (iOS 16 or iOS 17) ? Have you tried swizzling them yourself without the opentelemetry library, are they being calle in that situation?

[ddas09]

Have you tested with previous iOS versions (iOS 16 or iOS 17) ?
Yes, I have tested with multiple iOS version (emulator) and seeing this issue.

Have you tried swizzling them yourself without the opentelemetry library, are they being calle in that situation?
I tried swizzling the methods as per your suggesstion and still seeing the same issue.

As mentioned in earlier comments, I see - the delegate methods are only triggered when using a session created with a delegate, and when using the delegate-based API, i.e., dataTask(with:) without a completion handler -

let task = session.dataTask(with: request) // without any handler