Support compressed macOS DMG?

[tumagonx]

mac DMG compression according 7zip (which could open it) is using method: Copy Zero2 ZLIB CRC

Inside it usually there is one big archive.pax.gz which is normal gzip compression, which precomp can't reach because of above reason.

[tumagonx]

note: one could "resave" dmg into uncompressed one and precomp will recurse nicely, but the dmg will lose "originality"

compressed example: https://download.info.apple.com/Mac_OS_X/061-4046.20071114.Tgb8h/MacOSXUpd10.4.11Intel.dmg