zstd support

[Vinfall]

Zstandard is a loseless compression algorithm, and dual-licensed under BSD OR GPLv2.

WSL supports importing quite a few formats already like .tar., .tar.xz, .tar.gz and .tar.zst.

I'm aware of #109 and agree with the size increase worry. Regarding implementation, do you mean a go package for the compression algorithms or something else? If you mean packages, I think this or this would work.

To test if it's possible, I just blindly modified

wsldl/src/install/install.go

Lines 20 to 22 in 3672589

	var (
	defaultRootFiles = []string{"install.tar", "install.tar.gz", "rootfs.tar", "rootfs.tar.gz", "install.ext4.vhdx", "install.ext4.vhdx.gz"}
	)

and gladly importing .tar.zst just works. A more thorough support would require importing the package and change

wsldl/src/install/install.go

Lines 106 to 124 in 3672589

	// uncompress and copy
	rootPathLower := strings.ToLower(rootPath)
	if strings.HasSuffix(rootPathLower, ".gz") {
	// compressed with gzip
	gr, err := gzip.NewReader(src)
	if err != nil {
	return err
	}
	_, err = io.Copy(dest, gr)
	if err != nil {
	return err
	}
	} else {
	// not compressed
	_, err = io.Copy(dest, src)
	if err != nil {
	return err
	}
	}

or wherever I'm unaware of.

A test build of wsldl is available here and I successfully built DevuanWSL based on that. Running Devuan.exe does register the instance and it works flawlessly as far as I can tell so it should be feasible I guess.

[yuk7]

Ok, I understood.
I'll support it.

[yuk7]

I have released a new build that supports .tar.zst rootfs.
Please note that this may not be available in users version of WSL.

I will decide later whether to support zstd compression for vhd installs and backups.

[Vinfall]

I'll keep this open as it's just partially solved, but personally I use native WSL export and redirecting that to Zstandard works perfectly, thus having no preference on zstd compression support by wsldl.

Code snippet in case anyone is interested:

wsl --shutdown
cd path\to\distro
# Make sure to use cmd as PowerShell pipe is known to be problematic
cmd /c "wsl --export Devuan - | zstd -T0 -o Devuan-$(Get-Date -UFormat "%Y%m%d").tar.zst"