Add Helium backups support

[pierrezurek]

No description provided.

[nelenkov]

What is the Helium specific part about this? It looks you just added a tar library which extracts the tar archive, which you can also do with the tar command.

[pierrezurek]

Helium seems to use the same tar library instead of the Android Backup Service to pack the tar content inside the generated .ab file. Using android-backup-extractor's unpack function on an Helium .ab file gives an invalid .tar file (the tar command fails to extract it). Using the same library to unpack the Helium .ab seems to work fine.
Note : this new option also works fine with .ab files obtained with the adb backup command, maybe it could simply be called unpack-todir ? and we could just add a note somewhere to indicate Helium backups can be extracted with this option ?

[nelenkov]

OK, thanks. So it seems Helium produces broken tar files, not sure if it's a good idea to encourage this :)
Can you post a sample .ab archive and the resulting .tar file so I can look at it?

[pierrezurek]

[pierrezurek]

I added a .jpg extension to upload them here (right click and save as).

[HoverHell]

And it turns out this is still a problem.