NSURLSession may automatically retry the webview request started before app entering background

As decribed in http://www.openradar.me/39508158in ios 11.3 when app enters background, UIWebView will drop the current open connection, and as a result, the connection will get an connection lost error when enters the foreground again.

However the testing shows the behavior is different depending on how the testing is done. A recent testing on ios 11.4.1 device shows, when app enters background, the UIWebView's open xhr connection for a GET request is kept open, so uiwebview in the application does not get the connection close error when entering background or returning to foreground again. 

But, the server response for this original request is ignored somehow, and is not received by UIWebView's xhr request. 

Later, when the application enter foreground again, the fiddler shows NSURLSession automatically clone the original request, and send the new request to server. Once the server response for the new request is received by device, it is sent back to UIWebView's original xhr request for the UIWebView to process. 

So from the application's point of view, the original request is succeeded after the app enters background and returns to foreground again.

This behavior is described at Apple document 

 https://developer.apple.com/library/archive/qa/qa1941/_index.html