XHR requests are canceled in cordova-ios after the screen is locked

[akravchukabto]

Hi,
in our cordova ios app there is a case, when user can save form using xhr request.
In normal scenario when the Iphone screen is not locked after starting the save request - everything works fine.
But when the screen gets locked right after starting save request - request fails with error - Failed to load resource: The network connection was lost
I have made some research on this issue and found https://stackoverflow.com/questions/43505618/failed-to-load-resource-the-network-connection-was-lost-safari
It is said that WKWebView has been "optimized" to not make network connections while screen is locked
As far as I understand cordova-ios is using WKWebView so it may inherit this limitation.

1. Can you, please, clarify if this is expected behaviour for xhr requests to be canceled when the screen is locked on ios devices?
2. Are there any workarounds to deal with this issue - I mean, user starts save request, locks the screen, and request is completed successfully?

I have also tried using advanced http plugin https://github.com/silkimen/cordova-plugin-advanced-http#readme - the request is not canceled immediately, but when the time spent in background exceeds timeout - request is canceled by timeout.

The issue is observed on IOS platform only.
The issue is reproduced only on real device.
cordova ios version 6.3.0

Thank you for any help.

[akravchukabto]

Reply I got from Norman Breau in cordova slack channel:

I don't know about that specifically but iOS is known to limit background tasks pretty significantly. I'm pretty sure all WKWebView process stuff is paused if the app goes into the background and I don't think there is any real way around that, making browser-based solutions not appealing.
https://developer.apple.com/forums/thread/685525
States there are no "general purpose" background mechanism in iOS. Things just don't run in the background at all, however, specific APIs may have background modes. The NSURLSession is one API that does have a background mode so a request that has been started while the app in the foreground should continue to upload and/or download if the app goes into the background. See https://developer.apple.com/documentation/foundation/nsurlsessionconfiguration/1407496-backgroundsessionconfigurationwi?language=objc for more info on this.
You won't be able to rely on the browser's fetch/XMLHttpRequest APIs, but rather use a plugin that interfaces with the native API, and that API must set up a background networking task. I've never used this so I don't know if there are any caveats but I assume it's not really a good idea to assume that every request can be a background task. My guess the cordova-plugin-advanced-http plugin doesn't do this.