[hbornfree]

What's happening behind the scenes? Without knowing that it's hard to take the claim of 'no server involvement' at face value.

Does the sender have to be up for the receiever to receive?

[vbezhenar]

It seems to use WebRTC. Sender have to be up.

[www_harka_com]

Yes, sender has to up. Also the file must not be deleted. I checked both and the transfer was interrupted. Neat. :)

[mnw21cam]

The latter will surely depend on your operating system and its file handling semantics. In general, in Windows if something is reading a file and you delete the file, then you're actually deleting the file and the reader will be interrupted (assuming you manage to set it up in a way such that you actually can delete the file at all). In Linux, when you delete a file, you are actually unlinking the file from the directory, so the reader maintains a reference to the actual file and can carry on as normal. The free space will be reclaimed when the reference count decreases to zero when the reader closes the file.