Always pass chunks (#30)

It seems uncontroversially nice to default to dask.

tests/test_core.py

@@ -26,11 +26,16 @@ def test_to_xarray_with_bad_type():
 def test_to_xarray_reference_file(simple_reference_file):
     ds = to_xarray(simple_reference_file)
     assert ds
+    for da in ds.data_vars.values():
+        if da.ndim >= 2:
+            assert hasattr(da.data, "dask")
 
 
 def test_to_xarray_zarr(simple_zarr):
     ds = to_xarray(simple_zarr)
-    assert ds
+    for da in ds.data_vars.values():
+        if da.ndim >= 2:
+            assert hasattr(da.data, "dask"), da.name
 
 
 def test_to_xarray_zarr_with_open_kwargs_engine(complex_zarr):

xpystac/core.py

@@ -32,7 +32,7 @@ def _(
 
 @to_xarray.register
 def _(obj: pystac.Asset, **kwargs) -> xarray.Dataset:
-    default_kwargs: Mapping
+    default_kwargs: Mapping = {"chunks": {}}
     open_kwargs = obj.extra_fields.get("xarray:open_kwargs", {})
 
     storage_options = obj.extra_fields.get("xarray:storage_options", None)
@@ -52,24 +52,23 @@ def _(obj: pystac.Asset, **kwargs) -> xarray.Dataset:
             refs = planetary_computer.sign(r.json())
         except ImportError:
             refs = r.json()
+
         mapper = fsspec.get_mapper("reference://", fo=refs)
         default_kwargs = {
+            **default_kwargs,
             "engine": "zarr",
             "consolidated": False,
-            "chunks": {},
         }
         return xarray.open_dataset(
             mapper, **{**default_kwargs, **open_kwargs, **kwargs}
         )
 
     if obj.media_type == pystac.MediaType.COG:
         _import_optional_dependency("rioxarray")
-        default_kwargs = {"engine": "rasterio"}
+        default_kwargs = {**default_kwargs, "engine": "rasterio"}
     elif obj.media_type == "application/vnd+zarr":
         _import_optional_dependency("zarr")
-        default_kwargs = {"engine": "zarr"}
-    else:
-        default_kwargs = {}
+        default_kwargs = {**default_kwargs, "engine": "zarr"}
 
     ds = xarray.open_dataset(obj.href, **{**default_kwargs, **open_kwargs, **kwargs})
     return ds