background downloader poc

[jowparks]

This uses:
https://github.com/kesha-antonov/react-native-background-downloader

This is a fork of a fork, so we might want to fork ourselves and review the code 😅

In the install instructions it says you need to add code to your AppDelegate, for iOS. I skipped this, and it still seems to work 🤷

I took code from the example in the repo and massaged it to fit here as POC:

I have tested on iOS and it works out of the box. When I background the app, the downloads continue.
Clicked download, immediately background, then unbackgrounded 20 seconds later:

 LOG  task: progress {"bytesDownloaded": 735945, "bytesTotal": 20971520, "id": "1"}
 LOG  task: begin {"expectedBytes": 104857600, "headers": {"Accept-Ranges": "bytes", "Connection": "keep-alive", "Content-Length": "104857600", "Content-Type": "application/octet-stream", "Date": "Thu, 30 May 2024 23:14:33 GMT", "Etag": "\"64a6bb2c-6400000\"", "Last-Modified": "Thu, 06 Jul 2023 13:01:32 GMT", "Server": "nginx"}, "id": "3"}
 LOG  task: progress {"bytesDownloaded": 3881843, "bytesTotal": 50111000, "id": "2"}
 LOG  task: progress {"bytesDownloaded": 3701647, "bytesTotal": 20971520, "id": "1"}
 LOG  task: progress {"bytesDownloaded": 7928719, "bytesTotal": 20971520, "id": "1"}
 LOG  task: progress {"bytesDownloaded": 7846771, "bytesTotal": 50111000, "id": "2"}
 LOG  task: done {"id": "1"}
 LOG  task: done {"id": "2"}
 LOG  task: progress {"bytesDownloaded": 3227392, "bytesTotal": 104857600, "id": "3"}

[dguenther]

Hmm this looks pretty useful! Do you know if the app was fully suspended there? I was looking through this blog and it sounds like when the debugger is attached, the app won't fully suspend: https://www.avanderlee.com/swift/urlsession-common-pitfalls-with-background-download-upload-tasks/#5-attaching-the-xcode-debugger-prevents-your-app-from-suspending

I'd also be curious how the performance compares to just downloading the files directly.

[jowparks]

Hmm this looks pretty useful! Do you know if the app was fully suspended there? I was looking through this blog and it sounds like when the debugger is attached, the app won't fully suspend: https://www.avanderlee.com/swift/urlsession-common-pitfalls-with-background-download-upload-tasks/#5-attaching-the-xcode-debugger-prevents-your-app-from-suspending

I'd also be curious how the performance compares to just downloading the files directly.

Its hard to monitor performance for this because it starts a subsystem call to an NSURLSession, which is handled at a system level, all of the JS gets paused when the app is backgrounded and isn't run again until the app is foregrounded. I saw this when I was handling logging, nothing will happen in logging system until app is reforegrounded then all the logs for this stuff will get spit out at once. So trying to measure time while backgrounded is not trivial, maybe I missing something though.