Refactors v2 codec handling

src/zarr/codecs/_v2.py

@@ -5,20 +5,21 @@
 from typing import TYPE_CHECKING
 
 import numcodecs
-from numcodecs.compat import ensure_bytes, ensure_ndarray
+from numcodecs.compat import ensure_ndarray_like
 
-from zarr.abc.codec import ArrayArrayCodec, ArrayBytesCodec
-from zarr.core.buffer import Buffer, NDBuffer, default_buffer_prototype
+from zarr.abc.codec import ArrayBytesCodec
 from zarr.registry import get_ndbuffer_class
 
 if TYPE_CHECKING:
     import numcodecs.abc
 
     from zarr.core.array_spec import ArraySpec
+    from zarr.core.buffer import Buffer, NDBuffer
 
 
 @dataclass(frozen=True)
-class V2Compressor(ArrayBytesCodec):
+class V2Codec(ArrayBytesCodec):
+    filters: tuple[numcodecs.abc.Codec, ...] | None
     compressor: numcodecs.abc.Codec | None
 
     is_fixed_size = False
@@ -28,81 +29,61 @@ async def _decode_single(
         chunk_bytes: Buffer,
         chunk_spec: ArraySpec,
     ) -> NDBuffer:
-        if self.compressor is not None:
-            chunk_numpy_array = ensure_ndarray(
-                await asyncio.to_thread(self.compressor.decode, chunk_bytes.as_array_like())
-            )
+        cdata = chunk_bytes.as_array_like()
+        # decompress
+        if self.compressor:
+            chunk = await asyncio.to_thread(self.compressor.decode, cdata)
         else:
-            chunk_numpy_array = ensure_ndarray(chunk_bytes.as_array_like())
+            chunk = cdata
+
+        # apply filters
+        if self.filters:
+            for f in reversed(self.filters):
+                chunk = await asyncio.to_thread(f.decode, chunk)
+
+        # view as numpy array with correct dtype
+        chunk = ensure_ndarray_like(chunk)
+        # special case object dtype, because incorrect handling can lead to
+        # segfaults and other bad things happening
+        if chunk_spec.dtype != object:
+            chunk = chunk.view(chunk_spec.dtype)
+        elif chunk.dtype != object:
+            # If we end up here, someone must have hacked around with the filters.
+            # We cannot deal with object arrays unless there is an object
+            # codec in the filter chain, i.e., a filter that converts from object
+            # array to something else during encoding, and converts back to object
+            # array during decoding.
+            raise RuntimeError("cannot read object array without object codec")
 
-        # ensure correct dtype
-        if str(chunk_numpy_array.dtype) != chunk_spec.dtype and not chunk_spec.dtype.hasobject:
-            chunk_numpy_array = chunk_numpy_array.view(chunk_spec.dtype)
+        # ensure correct chunk shape
+        chunk = chunk.reshape(-1, order="A")
+        chunk = chunk.reshape(chunk_spec.shape, order=chunk_spec.order)
 
-        return get_ndbuffer_class().from_numpy_array(chunk_numpy_array)
+        return get_ndbuffer_class().from_ndarray_like(chunk)
 
     async def _encode_single(
-        self,
-        chunk_array: NDBuffer,
-        _chunk_spec: ArraySpec,
-    ) -> Buffer | None:
-        chunk_numpy_array = chunk_array.as_numpy_array()
-        if self.compressor is not None:
-            if (
-                not chunk_numpy_array.flags.c_contiguous
-                and not chunk_numpy_array.flags.f_contiguous
-            ):
-                chunk_numpy_array = chunk_numpy_array.copy(order="A")
-            encoded_chunk_bytes = ensure_bytes(
-                await asyncio.to_thread(self.compressor.encode, chunk_numpy_array)
-            )
-        else:
-            encoded_chunk_bytes = ensure_bytes(chunk_numpy_array)
-
-        return default_buffer_prototype().buffer.from_bytes(encoded_chunk_bytes)
-
-    def compute_encoded_size(self, _input_byte_length: int, _chunk_spec: ArraySpec) -> int:
-        raise NotImplementedError
-
-
-@dataclass(frozen=True)
-class V2Filters(ArrayArrayCodec):
-    filters: tuple[numcodecs.abc.Codec, ...] | None
-
-    is_fixed_size = False
-
-    async def _decode_single(
         self,
         chunk_array: NDBuffer,
         chunk_spec: ArraySpec,
-    ) -> NDBuffer:
-        chunk_ndarray = chunk_array.as_ndarray_like()
-        # apply filters in reverse order
-        if self.filters is not None:
-            for filter in self.filters[::-1]:
-                chunk_ndarray = await asyncio.to_thread(filter.decode, chunk_ndarray)
-
-        # ensure correct chunk shape
-        if chunk_ndarray.shape != chunk_spec.shape:
-            chunk_ndarray = chunk_ndarray.reshape(
-                chunk_spec.shape,
-                order=chunk_spec.order,
-            )
+    ) -> Buffer | None:
+        chunk = chunk_array.as_ndarray_like()
 
-        return get_ndbuffer_class().from_ndarray_like(chunk_ndarray)
+        # apply filters
+        if self.filters:
+            for f in self.filters:
+                chunk = await asyncio.to_thread(f.encode, chunk)
 
-    async def _encode_single(
-        self,
-        chunk_array: NDBuffer,
-        chunk_spec: ArraySpec,
-    ) -> NDBuffer | None:
-        chunk_ndarray = chunk_array.as_ndarray_like().ravel(order=chunk_spec.order)
+        # check object encoding
+        if ensure_ndarray_like(chunk).dtype == object:
+            raise RuntimeError("cannot write object array without object codec")
 
-        if self.filters is not None:
-            for filter in self.filters:
-                chunk_ndarray = await asyncio.to_thread(filter.encode, chunk_ndarray)
+        # compress
+        if self.compressor:
+            cdata = await asyncio.to_thread(self.compressor.encode, chunk)
+        else:
+            cdata = chunk
 
-        return get_ndbuffer_class().from_ndarray_like(chunk_ndarray)
+        return chunk_spec.prototype.buffer.from_bytes(cdata)
 
     def compute_encoded_size(self, _input_byte_length: int, _chunk_spec: ArraySpec) -> int:
         raise NotImplementedError

src/zarr/core/array.py

@@ -13,7 +13,7 @@
 from zarr._compat import _deprecate_positional_args
 from zarr.abc.store import Store, set_or_delete
 from zarr.codecs import _get_default_array_bytes_codec
-from zarr.codecs._v2 import V2Compressor, V2Filters
+from zarr.codecs._v2 import V2Codec
 from zarr.core.attributes import Attributes
 from zarr.core.buffer import (
     BufferPrototype,
@@ -118,9 +118,8 @@ def create_codec_pipeline(metadata: ArrayMetadata) -> CodecPipeline:
     if isinstance(metadata, ArrayV3Metadata):
         return get_pipeline_class().from_codecs(metadata.codecs)
     elif isinstance(metadata, ArrayV2Metadata):
-        return get_pipeline_class().from_codecs(
-            [V2Filters(metadata.filters), V2Compressor(metadata.compressor)]
-        )
+        v2_codec = V2Codec(filters=metadata.filters, compressor=metadata.compressor)
+        return get_pipeline_class().from_codecs([v2_codec])
     else:
         raise TypeError
 

tests/test_v2.py

@@ -121,3 +121,12 @@ async def test_create_dtype_str(dtype: Any) -> None:
     arr[:] = ["a", "bb", "ccc"]
     result = arr[:]
     np.testing.assert_array_equal(result, np.array(["a", "bb", "ccc"], dtype="object"))
+
+
+@pytest.mark.parametrize("filters", [[], [numcodecs.Delta(dtype="<i4")], [numcodecs.Zlib(level=2)]])
+def test_v2_filters_codecs(filters: Any) -> None:
+    array_fixture = [42]
+    arr = zarr.create(shape=1, dtype="<i4", zarr_format=2, filters=filters)
+    arr[:] = array_fixture
+    result = arr[:]
+    np.testing.assert_array_equal(result, array_fixture)