From aabb3d7ef961f726ab62b5cb89b6b995714ec3c6 Mon Sep 17 00:00:00 2001
From: Justus Magin <keewis@posteo.de>
Date: Sat, 30 Aug 2025 21:55:43 +0200
Subject: [PATCH 1/5] rename test_endian.py to test_bytes.py

---
 tests/test_codecs/{test_endian.py => test_bytes.py} | 0
 1 file changed, 0 insertions(+), 0 deletions(-)
 rename tests/test_codecs/{test_endian.py => test_bytes.py} (100%)

diff --git a/tests/test_codecs/test_endian.py b/tests/test_codecs/test_bytes.py
similarity index 100%
rename from tests/test_codecs/test_endian.py
rename to tests/test_codecs/test_bytes.py

From bde404ed8f6da24695fc204207cab70f755e85da Mon Sep 17 00:00:00 2001
From: Justus Magin <keewis@posteo.de>
Date: Sat, 30 Aug 2025 22:01:52 +0200
Subject: [PATCH 2/5] tests for `BytesCodec.to_dict`

---
 tests/test_codecs/test_bytes.py | 20 +++++++++++++++++++-
 1 file changed, 19 insertions(+), 1 deletion(-)

diff --git a/tests/test_codecs/test_bytes.py b/tests/test_codecs/test_bytes.py
index ab64afb1b8..0a96c53ae3 100644
--- a/tests/test_codecs/test_bytes.py
+++ b/tests/test_codecs/test_bytes.py
@@ -1,4 +1,4 @@
-from typing import Literal
+from typing import Any, Literal
 
 import numpy as np
 import pytest
@@ -58,3 +58,21 @@ async def test_endian_write(
     await _AsyncArrayProxy(a)[:, :].set(data)
     readback_data = await _AsyncArrayProxy(a)[:, :].get()
     assert np.array_equal(data, readback_data)
+
+
+@pytest.mark.parametrize(
+    ("endian", "expected"),
+    [
+        pytest.param(
+            "little", {"name": "bytes", "configuration": {"endian": "little"}}, id="little"
+        ),
+        pytest.param("big", {"name": "bytes", "configuration": {"endian": "big"}}, id="big"),
+        pytest.param(None, {"name": "bytes"}, id="missing"),
+    ],
+)
+def test_to_dict(endian: str, expected: dict[str, Any]) -> None:
+    codec = BytesCodec(endian=endian)
+
+    actual = codec.to_dict()
+
+    assert actual == expected

From cfad862405bb76e11defc1f6ef95ff3ab01bf4ed Mon Sep 17 00:00:00 2001
From: Justus Magin <keewis@posteo.de>
Date: Sat, 30 Aug 2025 22:07:57 +0200
Subject: [PATCH 3/5] tests for `from_dict` and roundtripping

---
 tests/test_codecs/test_bytes.py | 28 +++++++++++++++++++++++++++-
 1 file changed, 27 insertions(+), 1 deletion(-)

diff --git a/tests/test_codecs/test_bytes.py b/tests/test_codecs/test_bytes.py
index 0a96c53ae3..fd36cb4a29 100644
--- a/tests/test_codecs/test_bytes.py
+++ b/tests/test_codecs/test_bytes.py
@@ -5,7 +5,7 @@
 
 import zarr
 from zarr.abc.store import Store
-from zarr.codecs import BytesCodec
+from zarr.codecs import BytesCodec, Endian
 from zarr.storage import StorePath
 
 from .test_codecs import _AsyncArrayProxy
@@ -76,3 +76,29 @@ def test_to_dict(endian: str, expected: dict[str, Any]) -> None:
     actual = codec.to_dict()
 
     assert actual == expected
+
+
+@pytest.mark.parametrize(
+    ("mapping", "expected"),
+    [
+        pytest.param(
+            {"name": "bytes", "configuration": {"endian": "little"}}, Endian.little, id="little"
+        ),
+        pytest.param({"name": "bytes", "configuration": {"endian": "big"}}, Endian.big, id="big"),
+        pytest.param({"name": "bytes"}, None, id="missing"),
+    ],
+)
+def test_from_dict(mapping: dict[str, Any], expected: Endian | None) -> None:
+    actual = BytesCodec.from_dict(mapping)
+
+    assert actual.endian == expected
+
+
+@pytest.mark.parametrize("endian", ["little", "big", pytest.param(None, id="missing")])
+def test_roundtrip(endian: str | None) -> None:
+    codec = BytesCodec(endian=endian)
+
+    encoded = codec.to_dict()
+    roundtripped = BytesCodec.from_dict(encoded)
+
+    assert codec == roundtripped

From 1027f2c5a34e2d675d3c7602c2abb7364689ecee Mon Sep 17 00:00:00 2001
From: Justus Magin <keewis@posteo.de>
Date: Sat, 30 Aug 2025 22:09:09 +0200
Subject: [PATCH 4/5] don't use the system's default in `from_dict`

---
 src/zarr/codecs/bytes.py | 1 +
 1 file changed, 1 insertion(+)

diff --git a/src/zarr/codecs/bytes.py b/src/zarr/codecs/bytes.py
index 7576119c82..f5df964f90 100644
--- a/src/zarr/codecs/bytes.py
+++ b/src/zarr/codecs/bytes.py
@@ -50,6 +50,7 @@ def from_dict(cls, data: dict[str, JSON]) -> Self:
             data, "bytes", require_configuration=False
         )
         configuration_parsed = configuration_parsed or {}
+        configuration_parsed.setdefault("endian", None)
         return cls(**configuration_parsed)  # type: ignore[arg-type]
 
     def to_dict(self) -> dict[str, JSON]:

From 99243585452f4f5a5544ba58c149d870d827e186 Mon Sep 17 00:00:00 2001
From: Justus Magin <keewis@posteo.de>
Date: Sat, 30 Aug 2025 22:15:55 +0200
Subject: [PATCH 5/5] changelog

---
 changes/3417.bugfix.rst | 1 +
 1 file changed, 1 insertion(+)
 create mode 100644 changes/3417.bugfix.rst

diff --git a/changes/3417.bugfix.rst b/changes/3417.bugfix.rst
new file mode 100644
index 0000000000..51ff7049a6
--- /dev/null
+++ b/changes/3417.bugfix.rst
@@ -0,0 +1 @@
+Allow roundtripping ``BytesCodec`` instances to / from dict.