Handle structured fill_value parsing

Author: moradology

src/zarr/core/metadata/v2.py

@@ -315,6 +315,24 @@ def parse_metadata(data: ArrayV2Metadata) -> ArrayV2Metadata:
     return data
 
 
+def parse_structured_fill_value(fill_value: Any, dtype: np.dtype[Any]) -> Any:
+    """Handle structured dtype/fill value pairs"""
+    try:
+        if isinstance(fill_value, (tuple, list)):
+            fill_value = np.array([fill_value], dtype=dtype)[0]
+        elif isinstance(fill_value, bytes):
+            fill_value = np.frombuffer(fill_value, dtype=dtype)[0]
+        elif isinstance(fill_value, str):
+            decoded = base64.standard_b64decode(fill_value)
+            fill_value = np.frombuffer(decoded, dtype=dtype)[0]
+        else:
+            fill_value = np.array(fill_value, dtype=dtype)[()]
+    except Exception as e:
+        msg = f"Fill_value {fill_value} is not valid for dtype {dtype}."
+        raise ValueError(msg) from e
+    return fill_value
+
+
 def parse_fill_value(fill_value: Any, dtype: np.dtype[Any]) -> Any:
     """
     Parse a potential fill value into a value that is compatible with the provided dtype.
@@ -332,8 +350,9 @@ def parse_fill_value(fill_value: Any, dtype: np.dtype[Any]) -> Any:
     """
 
     if fill_value is None or dtype.hasobject:
-        # no fill value
         pass
+    elif dtype.fields is not None:
+        fill_value = parse_structured_fill_value(fill_value, dtype)
     elif not isinstance(fill_value, np.void) and fill_value == 0:
         # this should be compatible across numpy versions for any array type, including
         # structured arrays