The horrors of package formats, in Rust!

Flat files #

• Do I even need to say anything here? Horrible choice of package format, unless you’re distributing one file.

Tarballs #

• As far as I can tell, the tar crate can only unpack to a real directory on the filesystem, because nobody would ever have a use-case for extracting a tarball in-memory.
• The tar crate follows symlinks by default.
• Directories are an entry of type Directory and size 0.
• Symlinks are an entry of type Symlink and size 0.
• Symlinks have special extra metadata directly on the tar entry header.
• If you forget to set the checksum on an entry header, tooling may break in new and unhelpful ways.

Docker #

• lol
• Downloading an image, building an image, and uploading a rootfs tarball to the daemon are all the same command (CreateImage).
• An exported Docker image is a tarball of tarballs (that may contain more tarballs as part of the layer!) + some metadata.
• An exported Docker image may contain more than one image.
  • NOTE: I don’t remember the actual reason, but the metadata is an array which suggests that it’s possible.
• Everything about tarballs applies if you’re working with exporting or importing images.
• Yes, EVERYTHING.
• Docker’s external interface is basically just a glorified wrapper around tar. This is actually a good thing and doesn’t belong on this list.

Arch packages #

• All the metadata inside the package is optional, except for .PKGINFO. .MTREE and .BUILDINFO are optional.
• Version numbers MUST end in -\d+$ or similar. I’m not certain why and couldn’t find an answer. pacman will just refuse to install your package until you figure this out.
• .PKGINFO does not support quoted strings.
• builddate is optional and can be set to 0.
• size is optional and can be set to 0.

Part 2 soon, where we meet .deb, RPM, AppImage, and friends!