zstd / lz4 compression, block size

[mralusw]

It's not currently possible to tweak mksquashfs options, but, more perversely, the AppImage header makes damn sure that only xz/gzip embedded images work. It seems the kind of breakage where the developers had to write code to prevent a simple mount from just working.

I've tried hacking around this intentional breakage by calling --appimage-offset, then cat-ing the header and a recompressed squashfs, but the header checks the compression; since this header is an executable not a script, it can't be easily unbroken.

zstd should be able to achieve better compression. lz4 should be much, much faster, for the development stage. If not supported by default, it should be at least possible to tweak the AppImage more easily by hand.

[probonopd]

the AppImage header makes damn sure that only xz/gzip embedded images work

How so? The header mounts the thing. So it needs to be able to mount it.

There is a ticket for bringing in zstd support: #478