Single file kerchunking

tar_kerchunk.py

import kerchunk.hdf
import kerchunk.combine
import fsspec
import tarfile
import xarray as xr


ro = dict(
    s3={
        "anon": True,
        "client_kwargs": {"endpoint_url": "https://object-store.cloud.muni.cz"}
    }
)

# get offsets
with fsspec.open("s3://testfred/gridS.tar", **ro["s3"]) as tf:
    tar = tarfile.TarFile(fileobj=tf)
    offsets = {ti.name: ti.offset_data for ti in tar.getmembers()}

ofs = fsspec.open_files(
    # should have "first" caching strategy?
    "tar://*.nc::~/Downloads/gridS.tar", **ro
)
outs = {}
for of in ofs:
    with of as f:
        h = kerchunk.hdf.SingleHdf5ToZarr(f)
        outs[of.path] = h.translate()

mods = {}
for key, offset in offsets.items():
    out = outs[key]
    fs = fsspec.filesystem(
        "reference",
        fo=out,
        template_overrides={"u": f"tar://{key}"},
        remote_options={
            "fo": "s3://testfred/gridS.tar",
            "target_options": ro["s3"]
        }
    )
    mod = fs.references.copy()
    for k, v in mod.items():
        if isinstance(v, list):
            v[0] = "s3://testfred/gridS.tar"
            v[1] += offset
    mods[key] = mod

mzz = kerchunk.combine.MultiZarrToZarr(
    list(mods.values()),
    remote_options=ro["s3"],
    remote_protocol="s3",
    concat_dims=["time_counter"],
    identical_dims=['nav_lon', 'nav_lat']
)
out = mzz.translate()


ds = xr.open_zarr(
    "reference://",
    storage_options={
        "fo": out,
        "remote_options": ro["s3"]
    },
    consolidated=False
)
with open("gridS.json", "w") as j:
    import ujson
    ujson.dump(out, j)

ds.sivolu.mean(dim='time_counter').mean().compute()
# 0.9407204