Resolve a writer-side compressor spec to a zarr-codec list

Accepts a user-supplied compressor argument and returns a list list(id, level, ...) suitable for .zarr_compress() and for writing into a .zarray compressor field. NULL means "auto": Zstd when a Zstd codec package (currently zstdlite) is on the search path; otherwise zlib at the current package compression level. As of 2026 there is no maintained CRAN Zstd-bytes wrapper, so the auto path almost always lands on zlib; the resolver still picks Zstd if the user has installed a provider out of band.

Usage

.zarr_resolve_compressor(x = NULL, level = NULL)

Arguments

x

One of NULL, a string ("zstd", "gzip", "zlib", "blosc", "none"), or a list with at least an id field.

level

Override the codec level. When NULL, a per-codec default is used.

Value

Either NULL (no compression) or a list with id and typically level.