How to write a file from an iOS8 shared extension that a host application can read?

Question

I have a sharing extension in iOS8 that I call from Safari. After its launch, it has some data that it wants to share with the main application (for which both use a common application group), however, the data is too large to fill in the user settings, it needs to be saved as a file, How to write a file so that when loading my could he see the file in the main application?

For clarity, I'm not talking about downloading a remote file, the file is created in memory by a shared extension.

EDIT: spelling correction.