obstore implementations for .getsize and .getsize_prefix (#3227)

* obstore implementations for .getsize and .getsize_prefix

* rm comment

* rm typehint

---------

Co-authored-by: Davis Bennett <davis.v.bennett@gmail.com>

Author: slowjazz

changes/3227.feature.rst

@@ -0,0 +1 @@
+Add lightweight implementations of .getsize() and .getsize_prefix() for ObjectStore.

src/zarr/storage/_obstore.py

@@ -212,19 +212,21 @@ def supports_listing(self) -> bool:
         # docstring inherited
         return True
 
-    def list(self) -> AsyncGenerator[str, None]:
-        # docstring inherited
+    async def _list(self, prefix: str | None = None) -> AsyncGenerator[ObjectMeta, None]:
         import obstore as obs
 
-        objects: ListStream[Sequence[ObjectMeta]] = obs.list(self.store)
-        return _transform_list(objects)
+        objects: ListStream[Sequence[ObjectMeta]] = obs.list(self.store, prefix=prefix)
+        async for batch in objects:
+            for item in batch:
+                yield item
 
-    def list_prefix(self, prefix: str) -> AsyncGenerator[str, None]:
+    def list(self) -> AsyncGenerator[str, None]:
         # docstring inherited
-        import obstore as obs
+        return (obj["path"] async for obj in self._list())
 
-        objects: ListStream[Sequence[ObjectMeta]] = obs.list(self.store, prefix=prefix)
-        return _transform_list(objects)
+    def list_prefix(self, prefix: str) -> AsyncGenerator[str, None]:
+        # docstring inherited
+        return (obj["path"] async for obj in self._list(prefix))
 
     def list_dir(self, prefix: str) -> AsyncGenerator[str, None]:
         # docstring inherited
@@ -233,21 +235,21 @@ def list_dir(self, prefix: str) -> AsyncGenerator[str, None]:
         coroutine = obs.list_with_delimiter_async(self.store, prefix=prefix)
         return _transform_list_dir(coroutine, prefix)
 
+    async def getsize(self, key: str) -> int:
+        # docstring inherited
+        import obstore as obs
 
-async def _transform_list(
-    list_stream: ListStream[Sequence[ObjectMeta]],
-) -> AsyncGenerator[str, None]:
-    """
-    Transform the result of list into an async generator of paths.
-    """
-    async for batch in list_stream:
-        for item in batch:
-            yield item["path"]
+        resp = await obs.head_async(self.store, key)
+        return resp["size"]
+
+    async def getsize_prefix(self, prefix: str) -> int:
+        # docstring inherited
+        sizes = [obj["size"] async for obj in self._list(prefix=prefix)]
+        return sum(sizes)
 
 
 async def _transform_list_dir(
-    list_result_coroutine: Coroutine[Any, Any, ListResult[Sequence[ObjectMeta]]],
-    prefix: str,
+    list_result_coroutine: Coroutine[Any, Any, ListResult[Sequence[ObjectMeta]]], prefix: str
 ) -> AsyncGenerator[str, None]:
     """
     Transform the result of list_with_delimiter into an async generator of paths.

tests/test_store/test_object.py

@@ -75,6 +75,21 @@ def test_store_init_raises(self) -> None:
         with pytest.raises(TypeError):
             ObjectStore("path/to/store")
 
+    async def test_store_getsize(self, store: ObjectStore) -> None:
+        buf = cpu.Buffer.from_bytes(b"\x01\x02\x03\x04")
+        await self.set(store, "key", buf)
+        size = await store.getsize("key")
+        assert size == len(buf)
+
+    async def test_store_getsize_prefix(self, store: ObjectStore) -> None:
+        buf = cpu.Buffer.from_bytes(b"\x01\x02\x03\x04")
+        await self.set(store, "c/key1/0", buf)
+        await self.set(store, "c/key2/0", buf)
+        size = await store.getsize_prefix("c/key1")
+        assert size == len(buf)
+        total_size = await store.getsize_prefix("c")
+        assert total_size == len(buf) * 2
+
 
 @pytest.mark.slow_hypothesis
 def test_zarr_hierarchy():