Apple's documentation talks about handling the situation where a user runs out of disk space while downloading your In-App-Purchase content
Ensure that your app handles errors gracefully. For example, if the device runs out of disk space during a download, give the user the option to discard the partial download or to resume the download later when space becomes available.
But give no examples or clue at the best practise.
What is the best way to firstly recognise that they have run out of disk space during a download
and secondly how to resume the download later when space becomes available
?