is .zarr/ suffix strictly required? any other ".subsuffixes." considered (like in .ome.zarr)

[yarikoptic]

For DANDI we are considering to implement custom support for zarr "filesets" versioning.
There is an experimental webdav which is reverse proxied by apache at is https://dandi.centerforopenneuroscience.org .

What we discovered, is that despite the fact that our integration works just fine for URLs like https://kitware.github.io/itk-vtk-viewer/app/?gradientOpacity=0.3&image=https://dandiarchive.s3.amazonaws.com/zarr/6c18ad23-8bc9-404e-b902-d9ccb598dfca (BTW, doesn't work if you add trailing / since then it doesn't strip it before adding /.zattrs and fails), it does not work for https://kitware.github.io/itk-vtk-viewer/app/?gradientOpacity=0.3&image=https://dandi.centerforopenneuroscience.org/zarrs/6c1/8ad/6c18ad23-8bc9-404e-b902-d9ccb598dfca/c33f80763aafea111b5c51c291b22238-83143--96359783338 or with trailing / and you get just

with console showing

But if I add .zarr/ (through rewrite at apache level to remove .zarr for the forwarded to webdav URL) -- it works: https://kitware.github.io/itk-vtk-viewer/app/?gradientOpacity=0.3&image=https://dandi.centerforopenneuroscience.org/zarrs/6c1/8ad/6c18ad23-8bc9-404e-b902-d9ccb598dfca/c33f80763aafea111b5c51c291b22238-83143--96359783338.zarr

So the question is really - is .zarr suffix required for the tool? but then how come it works for original URL pointing to S3 prefix?

Also, looking forward -- is subsuffix, like .ome in .ome.zarr somehow important/used? (I hope not)

Thank you in advance for the answers/ideas.

[PaulHax]

Thanks for the well researched issue =)

The second URL is not recongzied as a zarr image because it has /zarrs/ rather than /zarr/ like the first URL. There is a regular expression testing if a image URL shall be treated as a zarr image:

itk-vtk-viewer/src/IO/ZarrMultiscaleSpatialImage.js

Lines 12 to 13 in 3622a93

	// ends with zarr and optional nested image name like foo.zarr/image1
	export const isZarr = url => /\w[./]zarr\b/.test(url)

So adding the .zarr at the end passes the RegEx test. A few more positive and negative zarr URL examples here:

itk-vtk-viewer/test/zarrTest.js

Lines 30 to 60 in 3622a93

	test('Test isZarr', t => {
	t.true(isZarr('foo.zarr'), 'no suffix')
	t.true(isZarr('foo.zarr/0'), '/0 suffix')
	t.true(isZarr('foo.zarr/asdf'), '/asdf suffix')
	t.true(isZarr('foo/zarr/asdf'), 'no dot before zarr')
	t.true(
	isZarr(
	'https://dandiarchive.s3.amazonaws.com/zarr/3d313fc2-0204-496d-bfa1-5c90951ee640'
	),
	'real url'
	)
	t.true(isZarr('https://site.com/zarr/a/b'), 'deep nested image')
	t.true(
	isZarr('https://site.com/foo.zarr/a/b'),
	'deep nested image with zarr as extension'
	)
	t.false(isZarr('zarr.asdf'), 'not when .asdf extension')
	t.false(
	isZarr('barzarr.asdf'),
	'not when .asdf extension withfilename barzarr'
	)
	t.false(
	isZarr('barzarr.asdf/asdf'),
	'not when .asdf extension and has suffix'
	)
	t.false(isZarr('foo.zarrX'), '.zarrX extension, not .zarr')
	t.end()
	})

Zarr URL format does seem to be a continual pain point:
#721

We could add another URL parameter &zarr that always treats the URL as a zarr image. Or change the toMulticalseSpatialImage logic:

itk-vtk-viewer/src/IO/toMultiscaleSpatialImage.js

Line 68 in 3622a93

if (isZarr(image.href)) {

.ome is not checked/used.

[yarikoptic]

+1 on adding explicit option to specify the format - "explicit better than implicit" they said while language is called after a part of the name of a movie coincidental with a full name of a snake...
What other formats do you consider that you can't/don't want to sense for having some /.zgroup or /.zattrs or even just trying to open it as a zarr for that URL?

[yarikoptic]

FYI, we now addressed this on our (dandidav) end by adding .zarr/ to those listings of zarrs so now we natively have https://dandi.centerforopenneuroscience.org/zarrs/001/e3b/001e3b6d-26fb-463f-af28-520a25680ab4/326273bcc8730474323a66ea4e3daa49-113328--97037755426.zarr/ and no analogous without .zarr/ (so examples above might no longer reproduce). Let us know if you would need/like to try on some older version