This is continuing the discussion in #2.

There, it was discovered that large files were not being uploaded correctly on MacOS. It appears that the beginning of the file was full of \x00 bytes. This kept us from figuring out the file type, but presumably this would also cause the file as uploaded to be broken. The same files that cause this problem work fine on a Linux system, so it's something specific to the Mac, it seems.

A couple of possibilities:

1. MacOS is writing the file full of null bytes first. Not sure why it would do this, nor why it only does this for large files.
2. Something is going wrong in llfuse, which is being used for MacOS. But I can't reproduce it with llfuse on Linux.
3. Something is going wrong in MacFuse.