Allow fsspec URLs in open_(mf)dataset

doc/io.rst

@@ -890,17 +890,44 @@ Cloud Storage Buckets
 
 It is possible to read and write xarray datasets directly from / to cloud
 storage buckets using zarr. This example uses the `gcsfs`_ package to provide
-a ``MutableMapping`` interface to `Google Cloud Storage`_, which we can then
-pass to xarray::
+an interface to `Google Cloud Storage`_.
+
+From v0.16.2: general `fsspec`_ URLs are parsed and the store set up for you
+automatically when reading, such that you can open a dataset in a single
+call. You should include any arguments to the storage backend as the
+key ``storage_options``, part of ``backend_kwargs``.
+
+.. code:: python
+
+    ds_gcs = xr.open_dataset(
+        "gcs://<bucket-name>/path.zarr",
+        backend_kwargs={
+            "storage_options": {"project": "<project-name>", "token": None}
+        },
+        engine="zarr",
+    )
+
+
+This also works with ``open_mfdataset``, allowing you to pass a list of paths or
+a URL to be interpreted as a glob string.
+
+For older versions, and for writing, you must explicitly set up a ``MutableMapping``
+instance and pass this, as follows:
+
+.. code:: python
 
     import gcsfs
-    fs = gcsfs.GCSFileSystem(project='<project-name>', token=None)
-    gcsmap = gcsfs.mapping.GCSMap('<bucket-name>', gcs=fs, check=True, create=False)
+
+    fs = gcsfs.GCSFileSystem(project="<project-name>", token=None)
+    gcsmap = gcsfs.mapping.GCSMap("<bucket-name>", gcs=fs, check=True, create=False)
     # write to the bucket
     ds.to_zarr(store=gcsmap)
     # read it back
     ds_gcs = xr.open_zarr(gcsmap)
 
+(or use the utility function ``fsspec.get_mapper()``).
+
+.. _fsspec: https://filesystem-spec.readthedocs.io/en/latest/
 .. _Zarr: http://zarr.readthedocs.io/
 .. _Amazon S3: https://aws.amazon.com/s3/
 .. _Google Cloud Storage: https://cloud.google.com/storage/

doc/whats-new.rst

@@ -56,6 +56,11 @@ New Features
   in the form of kwargs as well as a dict, like most similar methods.
   By `Maximilian Roos <https://github.com/max-sixty>`_.
 
+- :py:func:`open_dataset` and :py:func:`open_mfdataset` now accept ``fsspec`` URLs
+  (including globs for the latter) for ``engine="zarr"``, and so allow reading from
+  many remote and other file systems (:pull:`4461`)
+  By `Martin Durant <https://github.com/martindurant>`_
+
 Bug fixes
 ~~~~~~~~~
 - :py:meth:`DataArray.resample` and :py:meth:`Dataset.resample` do not trigger computations anymore if :py:meth:`Dataset.weighted` or :py:meth:`DataArray.weighted` are applied (:issue:`4625`, :pull:`4668`). By `Julius Busecke <https://github.com/jbusecke>`_.

xarray/backends/api.py

@@ -643,7 +643,9 @@ def open_dataarray(
     backend_kwargs: dict, optional
         A dictionary of keyword arguments to pass on to the backend. This
         may be useful when backend options would improve performance or
-        allow user control of dataset processing.
+        allow user control of dataset processing. If using fsspec URLs,
+        include the key "storage_options" to pass arguments to the
+        storage layer.
     use_cftime: bool, optional
         Only relevant if encoded dates come from a standard calendar
         (e.g. "gregorian", "proleptic_gregorian", "standard", or not
@@ -869,14 +871,33 @@ def open_mfdataset(
     .. [2] http://xarray.pydata.org/en/stable/dask.html#chunking-and-performance
     """
     if isinstance(paths, str):
-        if is_remote_uri(paths):
+        if is_remote_uri(paths) and engine == "zarr":
+            try:
+                from fsspec.core import get_fs_token_paths
+            except ImportError as e:
+                raise ImportError(
+                    "The use of remote URLs for opening zarr requires the package fsspec"
+                ) from e
+
+            fs, _, _ = get_fs_token_paths(
+                paths,
+                mode="rb",
+                storage_options=kwargs.get("backend_kwargs", {}).get(
+                    "storage_options", {}
+                ),
+                expand=False,
+            )
+            paths = fs.glob(fs._strip_protocol(paths))  # finds directories
+            paths = [fs.get_mapper(path) for path in paths]
+        elif is_remote_uri(paths):
             raise ValueError(
                 "cannot do wild-card matching for paths that are remote URLs: "
                 "{!r}. Instead, supply paths as an explicit list of strings.".format(
                     paths
                 )
             )
-        paths = sorted(glob(_normalize_path(paths)))
+        else:
+            paths = sorted(glob(_normalize_path(paths)))
     else:
         paths = [str(p) if isinstance(p, Path) else p for p in paths]
 

xarray/backends/zarr.py

@@ -1,5 +1,6 @@
 import os
 import pathlib
+from distutils.version import LooseVersion
 
 import numpy as np
 
@@ -295,6 +296,7 @@ def open_group(
         consolidated=False,
         consolidate_on_close=False,
         chunk_store=None,
+        storage_options=None,
         append_dim=None,
         write_region=None,
     ):
@@ -303,7 +305,15 @@ def open_group(
         if isinstance(store, pathlib.Path):
             store = os.fspath(store)
 
-        open_kwargs = dict(mode=mode, synchronizer=synchronizer, path=group)
+        open_kwargs = dict(
+            mode=mode,
+            synchronizer=synchronizer,
+            path=group,
+        )
+        if LooseVersion(zarr.__version__) >= "2.5.0":
+            open_kwargs["storage_options"] = storage_options
+        elif storage_options:
+            raise ValueError("Storage options only compatible with zarr>=2.5.0")
         if chunk_store:
             open_kwargs["chunk_store"] = chunk_store
 
@@ -537,6 +547,7 @@ def open_zarr(
     consolidated=False,
     overwrite_encoded_chunks=False,
     chunk_store=None,
+    storage_options=None,
     decode_timedelta=None,
     use_cftime=None,
     **kwargs,
@@ -649,6 +660,7 @@ def open_zarr(
         "consolidated": consolidated,
         "overwrite_encoded_chunks": overwrite_encoded_chunks,
         "chunk_store": chunk_store,
+        "storage_options": storage_options,
     }
 
     ds = open_dataset(
@@ -687,6 +699,7 @@ def open_dataset(
         consolidated=False,
         consolidate_on_close=False,
         chunk_store=None,
+        storage_options=None,
     ):
         store = ZarrStore.open_group(
             filename_or_obj,
@@ -696,6 +709,7 @@ def open_dataset(
             consolidated=consolidated,
             consolidate_on_close=consolidate_on_close,
             chunk_store=chunk_store,
+            storage_options=storage_options,
         )
 
         store_entrypoint = StoreBackendEntrypoint()

xarray/core/utils.py

@@ -645,7 +645,12 @@ def close_on_error(f):
 
 
 def is_remote_uri(path: str) -> bool:
-    return bool(re.search(r"^https?\://", path))
+    """Finds URLs of the form protocol:// or protocol::
+
+    This also matches for http[s]://, which were the only remote URLs
+    supported in <=v0.16.2.
+    """
+    return bool(re.search(r"^[a-z][a-z0-9]*(\://|\:\:)", path))
 
 
 def read_magic_number(filename_or_obj, count=8):

xarray/tests/__init__.py

@@ -73,6 +73,7 @@ def LooseVersion(vstring):
 has_nc_time_axis, requires_nc_time_axis = _importorskip("nc_time_axis")
 has_rasterio, requires_rasterio = _importorskip("rasterio")
 has_zarr, requires_zarr = _importorskip("zarr")
+has_fsspec, requires_fsspec = _importorskip("fsspec")
 has_iris, requires_iris = _importorskip("iris")
 has_cfgrib, requires_cfgrib = _importorskip("cfgrib")
 has_numbagg, requires_numbagg = _importorskip("numbagg")

xarray/tests/test_backends.py

@@ -54,6 +54,7 @@
     requires_cfgrib,
     requires_cftime,
     requires_dask,
+    requires_fsspec,
     requires_h5netcdf,
     requires_netCDF4,
     requires_pseudonetcdf,
@@ -3040,10 +3041,17 @@ def test_open_mfdataset(self):
 
         with raises_regex(IOError, "no files to open"):
             open_mfdataset("foo-bar-baz-*.nc")
-
         with raises_regex(ValueError, "wild-card"):
             open_mfdataset("http://some/remote/uri")
 
+    @requires_fsspec
+    def test_open_mfdataset_no_files(self):
+        pytest.importorskip("aiobotocore")
+
+        # glob is attempted as of #4823, but finds no files
+        with raises_regex(OSError, "no files"):
+            open_mfdataset("http://some/remote/uri", engine="zarr")
+
     def test_open_mfdataset_2d(self):
         original = Dataset({"foo": (["x", "y"], np.random.randn(10, 8))})
         with create_tmp_file() as tmp1:
@@ -4799,6 +4807,48 @@ def test_extract_zarr_variable_encoding():
         )
 
 
+@requires_zarr
+@requires_fsspec
+def test_open_fsspec():
+    import fsspec  # type: ignore
+    import zarr
+
+    if not hasattr(zarr.storage, "FSStore") or not hasattr(
+        zarr.storage.FSStore, "getitems"
+    ):
+        pytest.skip("zarr too old")
+
+    ds = open_dataset(os.path.join(os.path.dirname(__file__), "data", "example_1.nc"))
+
+    m = fsspec.filesystem("memory")
+    mm = m.get_mapper("out1.zarr")
+    ds.to_zarr(mm)  # old interface
+    ds0 = ds.copy()
+    ds0["time"] = ds.time + pd.to_timedelta("1 day")
+    mm = m.get_mapper("out2.zarr")
+    ds0.to_zarr(mm)  # old interface
+
+    # single dataset
+    url = "memory://out2.zarr"
+    ds2 = open_dataset(url, engine="zarr")
+    assert ds0 == ds2
+
+    # single dataset with caching
+    url = "simplecache::memory://out2.zarr"
+    ds2 = open_dataset(url, engine="zarr")
+    assert ds0 == ds2
+
+    # multi dataset
+    url = "memory://out*.zarr"
+    ds2 = open_mfdataset(url, engine="zarr")
+    assert xr.concat([ds, ds0], dim="time") == ds2
+
+    # multi dataset with caching
+    url = "simplecache::memory://out*.zarr"
+    ds2 = open_mfdataset(url, engine="zarr")
+    assert xr.concat([ds, ds0], dim="time") == ds2
+
+
 @requires_h5netcdf
 def test_load_single_value_h5netcdf(tmp_path):
     """Test that numeric single-element vector attributes are handled fine.