Add support for zstd compression via external tooling

This patchset has been forward-ported from the initial delta introduced in Ubuntu by @athos as mentioned in !65 (closed).

As you might know, Ubuntu has moved to zstd as the default compression algorithm used in dpkg, while this particular algorithm isn't implemented in Debian's dpkg. Furthermore, the Python packages shutil and tarfile don't support this algorithm either, which is why the approach used here is to invoke the zstd CLI as a subprocess, piping it the data.

mentioned in merge request !65 (closed)

approved this merge request

Looks good to me; I think it would be preferably if we could use the python-zstd module (also since that has fewer dependencies), but I think we can land this as is.

merged

mentioned in commit 94714ef0

I see this is now merged, but I just wanted to mention I successfully tested this patch in the context of our downstream project that uses python-debian: https://github.com/pulp/pulp_deb/issues/459#issuecomment-1096779025

Keep up the good work!

Any idea when this will release? We could really use it for the Ubuntu 22.04 release on April 21.

This will either way be too late for the April Ubuntu release.

I think it isn't all or nothing, even if there is no chance of a new deb package making it into Ubuntu in time for the release, availability on pypi.org (https://pypi.org/project/python-debian/) would satisfy all pip based use cases (like the Pulp project that I work on, so I am definitely biased).

And for people who are waiting an the deb package it is still true that the sooner the ball gets rolling the sooner the package will be ready/available somewhere (and if it's unstable or testing at first).

Just my 2ct.

FWIW, Ubuntu carries this patch (or a similar predecessor) as a delta anyway (which was introduced before jammy).