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A discussion on needed /paths properties and metadata #1851

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A discussion on needed /paths properties and metadata #1851

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c87cc8c
Just a discussion pasted from #1837
yarikoptic Feb 1, 2024
24e1188
First batch of annotations on what we have already or desire
yarikoptic Feb 1, 2024
e3c4500
Forgotten path
yarikoptic Feb 1, 2024
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codespell ;)
yarikoptic Feb 2, 2024
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21 changes: 21 additions & 0 deletions doc/design/paths-endpoint-webdav.md
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# Discussion on metadata needed for dandidav

Submitted as a PR to avoid spagetti thread discussion on https://github.com/dandi/dandi-archive/issues/1837#issuecomment-1921864949
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@jwodder listed needed properties and metadata fields:

* Asset properties used by dandidav:
* `asset_id` (PRESENT)
* `blob_id`
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what for do we need blob_id if we have contentUrl?

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@jwodder jwodder Feb 1, 2024 •
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The contentUrl returned in .../assets/paths/ responses is a plain S3 URL, and serving it to the user in a web browser would result in the file being downloaded and named with the blob ID. In order for the downloaded file to be named with the asset's filename instead, we need a signed S3 URL, which is obtained via the API download URL in the contentUrl field of the metadata.

EDIT: Sorry, I misinterpreted the question. For blob ID, the code just checks whether blob_id or zarr_id is non-None in order to determine whether the asset is a blob or a Zarr.

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ok, so we the actually need result_type (Folder, AssetBlob, AssetZarr) as I suggested in #1837 (comment) .

* `zarr_id`
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I guess zarr_id is needed for traversal etc? or could contentUrl version be used? (probably we do not want to rely on parsing it).

So it feels that we might ask for asset record to include blob_id (although not sure what for yet exactly) and zarr_id, hence

Suggested change
* `zarr_id`
* `zarr_id` (DESIRED)

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dandidav does parse S3 contentUrls, as that's necessary in order to discover the name of the S3 bucket without hardcoding it or requiring it to be passed on the command line.

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so in principle we can just parse out bucket, zarr_id and blob_id from contenturl, correct?

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Yes, but I'd rather dandidav not have to make too many assumptions about how our S3 URLs are structured.

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agree. We would only need to be able to construct zarr "http s3" URLs from manifests so it would need to know that , right?
For blobs -- contentUrl should be good enough.

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Note that asset metadata lists two contentUrls, an unsigned S3 URL and an API download URL of the form https://api.dandiarchive.org/api/assets/{asset_id}/download/.

  • For Zarr assets, dandidav needs the S3 URL in order to know how to query the Zarr's entries from S3.

  • However, for blob assets, dandidav currently uses the API download URL, as it provides a better UX. Specifically, if dandidav were to redirect GET requests for a blob to the blob's unsigned S3 URL, then the browser would save the response to a file named after the last component of the S3 URL, which is (always?) the blob ID. In order to get the downloaded files to be named after the filename portion of the asset's path instead, a signed S3 URL with a Content-Disposition has to be used, and that is acquired by redirecting to the API download URL, which in turn redirects to such a signed S3 URL.

* `path` (PRESENT)
* `size` (PRESENT)
* `created` (GOOD TO HAVE)
* `modified` (SUGGESTED to be included)
* Note: It might be more accurate to use the `blobDateModified` metadata field for this instead; cf. dandi/dandidav#17

* Asset metadata used by dandidav:
* `encodingFormat` (blobs only) (STRONGLY DESIRED but not REQUIRED)
* `contentUrl` (API download URL for blobs, S3 URL for Zarrs) (INCLUDED)
* `digest["dandi:dandi-etag"]` (blobs only)
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what this one for?

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Etag (reported in PROPFIND responses)

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in principle could be any other checksum I guess , right?

note: I thought that besides ETag functionality a commonly known checksum could then be used by receiving end to validate the download if that would be the target purpose for such a listing.

for versioned zarrs we would need "dandi:dandi-zarr-checksum" to use in conjunction with the zarr_id.

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Well, the dandi:dandi-etag is the same as the ETag header reported by S3 when downloading a blob asset. In contrast, there's no single file that has a dandi:dandi-zarr-checksum as an ETag.

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I meant that we can use dandi:dandi-zarr-checksum as a value for ETag on zarr collections (folders).

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I'm not sure if it makes sense to apply etags to collections, as GETing a collection won't give you a response with that etag. (Cf. dandi/dandidav#26)

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