Use UTF-8 for filename encoding instead of ASCII

src/littlefs/lfs.pyx

@@ -8,8 +8,13 @@ from littlefs.context import UserContext
 from littlefs import errors
 
 
-FILENAME_ENCODING = 'ascii'
-"""Default filename encoding"""
+FILENAME_ENCODING = 'utf-8'
+"""Default filename encoding.
+
+littlefs stores names as opaque byte strings, so any encoding works on the
+C side. UTF-8 is used so that non-ASCII filenames are supported; since ASCII
+is a strict subset of UTF-8, existing ASCII names encode/decode identically.
+"""
 
 class LFSStat(NamedTuple):
     """Littlefs File / Directory status."""

test/test_unicode_filenames.py

@@ -0,0 +1,66 @@
+import pytest
+
+from littlefs import LittleFS
+
+# A mix of Latin-1, CJK and astral-plane (emoji) characters to exercise
+# multi-byte UTF-8 sequences.
+UNICODE_NAMES = ["café.txt", "日本語.bin", "emoji_😀.dat"]
+
+
+@pytest.fixture(scope="function")
+def fs():
+    yield LittleFS(block_size=128, block_count=64)
+
+
+@pytest.mark.parametrize("name", UNICODE_NAMES)
+def test_open_write_read_roundtrip(fs, name):
+    payload = name.encode("utf-8")
+    with fs.open(name, "wb") as f:
+        f.write(payload)
+    with fs.open(name, "rb") as f:
+        assert f.read() == payload
+
+
+@pytest.mark.parametrize("name", UNICODE_NAMES)
+def test_stat_preserves_name(fs, name):
+    with fs.open(name, "wb") as f:
+        f.write(b"x")
+    assert fs.stat(name).name == name
+
+
+def test_listdir_roundtrips_unicode(fs):
+    for name in UNICODE_NAMES:
+        with fs.open(name, "wb") as f:
+            f.write(b"x")
+    assert set(fs.listdir("/")) == set(UNICODE_NAMES)
+
+
+@pytest.mark.parametrize("name", UNICODE_NAMES)
+def test_mkdir_and_nested_file(fs, name):
+    fs.mkdir(name)
+    assert name in fs.listdir("/")
+    nested = name + "/inner_£.txt"
+    with fs.open(nested, "wb") as f:
+        f.write(b"x")
+    assert fs.stat(nested).name == "inner_£.txt"
+
+
+@pytest.mark.parametrize("name", UNICODE_NAMES)
+def test_rename_and_remove(fs, name):
+    with fs.open(name, "wb") as f:
+        f.write(b"x")
+    renamed = "renamed_" + name
+    fs.rename(name, renamed)
+    assert renamed in fs.listdir("/")
+    assert name not in fs.listdir("/")
+    fs.remove(renamed)
+    assert renamed not in fs.listdir("/")
+
+
+def test_ascii_names_still_work(fs):
+    """ASCII is a strict subset of UTF-8: existing names must be unaffected."""
+    with fs.open("plain.txt", "wb") as f:
+        f.write(b"hello")
+    with fs.open("plain.txt", "rb") as f:
+        assert f.read() == b"hello"
+    assert fs.stat("plain.txt").name == "plain.txt"