Add support for Zarr V3

[ChrisJohnNOAA]

Currently we support zarr through the netcdf-java, specifically the cdf-zarr module.

We want to support reading and writing of zarr v3. There's a library from the zarr community that I believe supports this:
https://github.com/zarr-developers/zarr-java

I believe the api is very similar to the current netcdf-java implementation.
The main locations that interact with zarr files currently are:
https://github.com/ERDDAP/erddap/blob/3e00aa716e42f0164173951f3bf27efee19fe80d/WEB-INF/classes/gov/noaa/pfel/erddap/dataset/EDDGridFromFiles.java
https://github.com/ERDDAP/erddap/blob/3e00aa716e42f0164173951f3bf27efee19fe80d/WEB-INF/classes/gov/noaa/pfel/erddap/dataset/EDDTableFromFiles.java
https://github.com/ERDDAP/erddap/blob/3e00aa716e42f0164173951f3bf27efee19fe80d/WEB-INF/classes/gov/noaa/pfel/coastwatch/util/FileVisitorDNLS.java

Zarr support was added into the EDD*FromFiles dataset types because it was using the existing netcdf calls to load the files. Given Zarr's differences (what's a system level file for other data types is a folder in zarr) and moving to a new library for reading the files, it might make sense to have EDD*FromZarrFiles as new dataset types.

If we do this, we should also look into how we can assist admins in migrating from the old EDD*FromFiles datasets to the new EDD*FromZarrFiles.

[Nesar976]

Hi @ChrisJohnNOAA, thanks for the detailed context and links.

I’m interested in looking into Zarr v3 support and how zarr-java could fit into ERDDAP’s current dataset handling (or whether a separate EDDFromZarrFiles type makes more sense). I’m also planning to apply for GSoC 2026, and this issue aligns well with what I’d like to work on.

I’ll start by reviewing the existing NetCDF/Zarr flow and share thoughts on a possible approach. Please let me know if there’s a preferred starting point.

[ChrisJohnNOAA]

Hi @Nesar976 I appreciate your interest!

Reviewing the existing code and communicating your proposed approach for using zarr-java is a great way to get started on the project.

[Nesar976]

Hi @ChrisJohnNOAA,

I’m currently reviewing the existing NetCDF/Zarr integration and evaluating how zarr-java would fit for Zarr v3 support. I’m finalizing a proposed approach and will raise a PR based on this shortly.

I’ll share updates as I make progress.