I am observing progress of a download in the totally normal way …

let task = URLSession.shared.dataTask(with: req) { (_,_,_) in
...
}

___obs = task.progress.observe(.fractionCompleted) { prog, _ in
    print("frac ", prog.fractionCompleted)
}

task.resume()

In doing any large download (say 500mb, ten seconds) the output is useless,

data start arriving, 0 seconds
>>>>>> ... 0.950
>>>>>> ... 0.951
>>>>>> ... 0.951
>>>>>> ... 0.952
>>>>>> ... 0.952
>>>>>> ... 0.953
>>>>>> ... 1.000 .. we're now about 0.5 seconds later!
500mb completes about 10 seconds later

• the observation is only called a few times, during the first (say) 20-30mb, first half second or so

• it quickly runs up to “1” and stops

• the remaining 470mb download then comes in the next ~9 seconds

• note there is some dispute which order the two lines or code observe/resume should appear, I tried both extensively, no difference. Yes, ___obs is of course retained.

• this is iOS17. I’ve never previously noticed task.progress being “totally useless” but of course it could just be I didn’t notice

• could (IDK) this be due to some server issue (headers, something?)

• one point, has anyone actually observed (pun) the fractionCompleted actually working well on a real world large file? That would be a good data point.

Total mystery to me I’ve fiddled with for an hour.