Add support for zstd compression to libappimage

[philmb3487]

There seems to be an issue with icon generation on a newer runtime of appimagetool.

Could someone with more experience have a look at the bug report I filed here? https://github.com/ivan-hc/Steam-appimage/issues/27

Where is the snafu with image generation in this case?

thumbnail managers should adapt to the work of AppImage packagers, not the other way around

Is this the policy of the project?

Thanks!

[probonopd]

Can you summarize what is the issue there and how we might be able to help?

An AppImage thumbnailer would need to retrieve the .DirIcon from inside the AppImage.

[philmb3487]

Yes, I can summarize. The gist of it is that some people are generating AppImages with zstd compression, and that is not supported out of the box by libappimage. Now, that is fine for executing AppImages, but file thumbnailers such as KDE's Dolphin use libappimage.so directly to peek at the .DirIcon information, which fails for zstd images.

Would it be possible to add this support?

Arch Linux seems to enable fuse to get that support, squashfuse then needs to be compiled with zstd support turned on. That's a lot of switches that might or might not be enabled, depending on the distribution, and I think thumbnails should always be available in any case.

See my findings here, https://github.com/ivan-hc/Steam-appimage/issues/27#issuecomment-2365229961

So, I propose either,

1) better zstd support out of the box, 2) document what needs to be done if Thumbnails cannot be shown on some appimages (out of the box it would be fine with xz, zip images,

Squashfs image uses (null) compression, this version supports only xz, zlib.
ERROR: appimage_read_file_into_buffer_following_symlinks : sqfs_open_image error: /home/phil/Applications/Steam-1.0.0.81-2-3-x86_64.appimage

[probonopd]

Hi @philmb3487, thanks for summarizing. This seems to be a feature request for libappimage then and should go here:

• https://github.com/AppImageCommunity/libappimage/issues/193