Bug#833697: diffoscope: libarchive.exception.ArchiveError when running on two dmg files

[David Fifield]

It seems that the error lies in the handling of the dmg layer. If I
manually extract the dmg files using 7z from the p7zip-full package,
then diffoscope doesn't crash. I.e.,

mkdir -p 20160806-6.5a1-965e0daa7d59{,-2}/m
7z x 20160806-6.5a1-965e0daa7d59/TorBrowser-6.5a1-osx64_en-US.dmg -o20160806-6.5a1-965e0daa7d59/m
7z x 20160806-6.5a1-965e0daa7d59-2/TorBrowser-6.5a1-osx64_en-US.dmg -o20160806-6.5a1-965e0daa7d59-2/m
diffoscope --text diff.txt 20160806-6.5a1-965e0daa7d59{,-2}/m

diffoscope seems to treat the dmg file as a bzip2-compressed iso9660
filesystem image, when it is something more than that. Here is how the
dmg file is being created. I don't know exactly what the libdmg-hfsplus
command is doing.

https://gitweb.torproject.org/builders/tor-browser-bundle.git/tree/gitian/build-helpers/ddmg.sh?id=ce368417b914f74383bafddd268b2f1a2e9dc509

...
genisoimage -D -V "Tor Browser" -no-pad -R -apple -o ~/build/tbb-uncompressed.dmg -path-list ~/build/filelist.txt -graft-points -gid 20 -dir-mode $EXE_MODE -new-dir-mode $EXE_MODE
cd ~/build
~/build/libdmg-hfsplus/dmg/dmg dmg tbb-uncompressed.dmg $DMGFILE