feat: add SupportsSetRange protocol and store implementations

changes/3907.feature.md

@@ -0,0 +1 @@
+Add protocols for stores that support byte-range-writes. This is necessary to support in-place writes of sharded arrays.

src/zarr/abc/store.py

@@ -22,6 +22,7 @@
     "Store",
     "SupportsDeleteSync",
     "SupportsGetSync",
+    "SupportsSetRange",
     "SupportsSetSync",
     "SupportsSyncStore",
     "set_or_delete",
@@ -709,6 +710,23 @@ async def delete(self) -> None: ...
     async def set_if_not_exists(self, default: Buffer) -> None: ...
 
 
+@runtime_checkable
+class SupportsSetRange(Protocol):
+    """Protocol for stores that support writing to a byte range within an existing value.
+
+    Overwrites ``len(value)`` bytes starting at byte offset ``start`` within the
+    existing stored value for ``key``. The key must already exist and the write
+    must fit within the existing value (i.e., ``start + len(value) <= len(existing)``).
+
+    Behavior when the write extends past the end of the existing value is
+    implementation-specific and should not be relied upon.
+    """
+
+    async def set_range(self, key: str, value: Buffer, start: int) -> None: ...
+
+    def set_range_sync(self, key: str, value: Buffer, start: int) -> None: ...
+
+
 @runtime_checkable
 class SupportsGetSync(Protocol):
     def get_sync(

src/zarr/storage/_local.py

@@ -16,6 +16,7 @@
     RangeByteRequest,
     Store,
     SuffixByteRequest,
+    SupportsSetRange,
 )
 from zarr.core.buffer import Buffer
 from zarr.core.buffer.core import default_buffer_prototype
@@ -77,6 +78,13 @@ def _atomic_write(
         raise
 
 
+def _put_range(path: Path, value: Buffer, start: int) -> None:
+    """Write bytes at a specific offset within an existing file."""
+    with path.open("r+b") as f:
+        f.seek(start)
+        f.write(value.as_numpy_array().tobytes())
+
+
 def _put(path: Path, value: Buffer, exclusive: bool = False) -> int:
     path.parent.mkdir(parents=True, exist_ok=True)
     # write takes any object supporting the buffer protocol
@@ -85,7 +93,7 @@ def _put(path: Path, value: Buffer, exclusive: bool = False) -> int:
         return f.write(view)
 
 
-class LocalStore(Store):
+class LocalStore(Store, SupportsSetRange):
     """
     Store for the local file system.
 
@@ -292,6 +300,19 @@ async def _set(self, key: str, value: Buffer, exclusive: bool = False) -> None:
         path = self.root / key
         await asyncio.to_thread(_put, path, value, exclusive=exclusive)
 
+    async def set_range(self, key: str, value: Buffer, start: int) -> None:
+        if not self._is_open:
+            await self._open()
+        self._check_writable()
+        path = self.root / key
+        await asyncio.to_thread(_put_range, path, value, start)
+
+    def set_range_sync(self, key: str, value: Buffer, start: int) -> None:
+        self._ensure_open_sync()
+        self._check_writable()
+        path = self.root / key
+        _put_range(path, value, start)
+
     async def delete(self, key: str) -> None:
         """
         Remove a key from the store.

src/zarr/storage/_memory.py

@@ -3,7 +3,7 @@
 from logging import getLogger
 from typing import TYPE_CHECKING, Any, Self
 
-from zarr.abc.store import ByteRequest, Store
+from zarr.abc.store import ByteRequest, Store, SupportsSetRange
 from zarr.core.buffer import Buffer, gpu
 from zarr.core.buffer.core import default_buffer_prototype
 from zarr.core.common import concurrent_map
@@ -18,7 +18,7 @@
 logger = getLogger(__name__)
 
 
-class MemoryStore(Store):
+class MemoryStore(Store, SupportsSetRange):
     """
     Store for local memory.
 
@@ -186,6 +186,26 @@ async def delete(self, key: str) -> None:
         except KeyError:
             logger.debug("Key %s does not exist.", key)
 
+    def _set_range_impl(self, key: str, value: Buffer, start: int) -> None:
+        buf = self._store_dict[key]
+        target = buf.as_numpy_array()
+        if not target.flags.writeable:
+            target = target.copy()
+            self._store_dict[key] = buf.__class__(target)
+        source = value.as_numpy_array()
+        target[start : start + len(source)] = source
+
+    async def set_range(self, key: str, value: Buffer, start: int) -> None:
+        self._check_writable()
+        await self._ensure_open()
+        self._set_range_impl(key, value, start)
+
+    def set_range_sync(self, key: str, value: Buffer, start: int) -> None:
+        self._check_writable()
+        if not self._is_open:
+            self._is_open = True
+        self._set_range_impl(key, value, start)
+
     async def list(self) -> AsyncIterator[str]:
         # docstring inherited
         for key in self._store_dict:

tests/test_store/test_local.py

@@ -10,6 +10,7 @@
 
 import zarr
 from zarr import create_array
+from zarr.abc.store import SupportsSetRange
 from zarr.core.buffer import Buffer, cpu
 from zarr.core.sync import sync
 from zarr.storage import LocalStore
@@ -162,6 +163,54 @@ def test_get_json_sync_with_prototype_none(
         result = store._get_json_sync(key, prototype=buffer_cls)
         assert result == data
 
+    def test_supports_set_range(self, store: LocalStore) -> None:
+        """LocalStore should implement SupportsSetRange."""
+        assert isinstance(store, SupportsSetRange)
+
+    @pytest.mark.parametrize(
+        ("start", "patch", "expected"),
+        [
+            (0, b"XX", b"XXAAAAAAAA"),
+            (3, b"XX", b"AAAXXAAAAA"),
+            (8, b"XX", b"AAAAAAAAXX"),
+            (0, b"ZZZZZZZZZZ", b"ZZZZZZZZZZ"),
+            (5, b"B", b"AAAAABAAAA"),
+            (0, b"BCDE", b"BCDEAAAAAA"),
+        ],
+        ids=["start", "middle", "end", "full-overwrite", "single-byte", "multi-byte-start"],
+    )
+    async def test_set_range(
+        self, store: LocalStore, start: int, patch: bytes, expected: bytes
+    ) -> None:
+        """set_range should overwrite bytes at the given offset."""
+        await store.set("test/key", cpu.Buffer.from_bytes(b"AAAAAAAAAA"))
+        await store.set_range("test/key", cpu.Buffer.from_bytes(patch), start=start)
+        result = await store.get("test/key", prototype=cpu.buffer_prototype)
+        assert result is not None
+        assert result.to_bytes() == expected
+
+    @pytest.mark.parametrize(
+        ("start", "patch", "expected"),
+        [
+            (0, b"XX", b"XXAAAAAAAA"),
+            (3, b"XX", b"AAAXXAAAAA"),
+            (8, b"XX", b"AAAAAAAAXX"),
+            (0, b"ZZZZZZZZZZ", b"ZZZZZZZZZZ"),
+            (5, b"B", b"AAAAABAAAA"),
+            (0, b"BCDE", b"BCDEAAAAAA"),
+        ],
+        ids=["start", "middle", "end", "full-overwrite", "single-byte", "multi-byte-start"],
+    )
+    def test_set_range_sync(
+        self, store: LocalStore, start: int, patch: bytes, expected: bytes
+    ) -> None:
+        """set_range_sync should overwrite bytes at the given offset."""
+        sync(store.set("test/key", cpu.Buffer.from_bytes(b"AAAAAAAAAA")))
+        store.set_range_sync("test/key", cpu.Buffer.from_bytes(patch), start=start)
+        result = store.get_sync(key="test/key", prototype=cpu.buffer_prototype)
+        assert result is not None
+        assert result.to_bytes() == expected
+
 
 @pytest.mark.parametrize("exclusive", [True, False])
 def test_atomic_write_successful(tmp_path: pathlib.Path, exclusive: bool) -> None:

tests/test_store/test_memory.py

@@ -9,6 +9,7 @@
 import pytest
 
 import zarr
+from zarr.abc.store import SupportsSetRange
 from zarr.core.buffer import Buffer, cpu, gpu
 from zarr.core.sync import sync
 from zarr.errors import ZarrUserWarning
@@ -127,6 +128,55 @@ def test_get_json_sync_with_prototype_none(
         result = store._get_json_sync(key, prototype=buffer_cls)
         assert result == data
 
+    def test_supports_set_range(self, store: MemoryStore) -> None:
+        """MemoryStore should implement SupportsSetRange."""
+        assert isinstance(store, SupportsSetRange)
+
+    @pytest.mark.parametrize(
+        ("start", "patch", "expected"),
+        [
+            (0, b"XX", b"XXAAAAAAAA"),
+            (3, b"XX", b"AAAXXAAAAA"),
+            (8, b"XX", b"AAAAAAAAXX"),
+            (0, b"ZZZZZZZZZZ", b"ZZZZZZZZZZ"),
+            (5, b"B", b"AAAAABAAAA"),
+            (0, b"BCDE", b"BCDEAAAAAA"),
+        ],
+        ids=["start", "middle", "end", "full-overwrite", "single-byte", "multi-byte-start"],
+    )
+    async def test_set_range(
+        self, store: MemoryStore, start: int, patch: bytes, expected: bytes
+    ) -> None:
+        """set_range should overwrite bytes at the given offset."""
+        await store.set("test/key", cpu.Buffer.from_bytes(b"AAAAAAAAAA"))
+        await store.set_range("test/key", cpu.Buffer.from_bytes(patch), start=start)
+        result = await store.get("test/key", prototype=cpu.buffer_prototype)
+        assert result is not None
+        assert result.to_bytes() == expected
+
+    @pytest.mark.parametrize(
+        ("start", "patch", "expected"),
+        [
+            (0, b"XX", b"XXAAAAAAAA"),
+            (3, b"XX", b"AAAXXAAAAA"),
+            (8, b"XX", b"AAAAAAAAXX"),
+            (0, b"ZZZZZZZZZZ", b"ZZZZZZZZZZ"),
+            (5, b"B", b"AAAAABAAAA"),
+            (0, b"BCDE", b"BCDEAAAAAA"),
+        ],
+        ids=["start", "middle", "end", "full-overwrite", "single-byte", "multi-byte-start"],
+    )
+    def test_set_range_sync(
+        self, store: MemoryStore, start: int, patch: bytes, expected: bytes
+    ) -> None:
+        """set_range_sync should overwrite bytes at the given offset."""
+        store._is_open = True
+        store._store_dict["test/key"] = cpu.Buffer.from_bytes(b"AAAAAAAAAA")
+        store.set_range_sync("test/key", cpu.Buffer.from_bytes(patch), start=start)
+        result = store.get_sync(key="test/key", prototype=cpu.buffer_prototype)
+        assert result is not None
+        assert result.to_bytes() == expected
+
 
 # TODO: fix this warning
 @pytest.mark.filterwarnings("ignore:Unclosed client session:ResourceWarning")