fix: keep attribute preservation best-effort when os.utime fails

media_shrinker.py

@@ -700,12 +700,12 @@ def preserve_file_attributes(
 
     _copy_extended_attributes(source, dest)
 
-    os.utime(dest, ns=(source_stat.st_atime_ns, source_stat.st_mtime_ns))
+    _restore_timestamps(source_stat, dest)
 
     resolved_setfile = setfile_path if setfile_path is not None else _get_setfile_path()
     if resolved_setfile:
         _copy_macos_creation_time(source_stat, dest, resolved_setfile)
-        os.utime(dest, ns=(source_stat.st_atime_ns, source_stat.st_mtime_ns))
+        _restore_timestamps(source_stat, dest)
 
 
 def convert_file(
@@ -1630,6 +1630,19 @@ def _resolve_collision(path: Path, *, overwrite: bool) -> Path:
     raise FileExistsError(f"Could not find free output path for {path}")
 
 
+def _restore_timestamps(source_stat: os.stat_result, dest: Path) -> None:
+    """Best-effort copy of nanosecond atime/mtime from source_stat onto dest.
+
+    A read-only destination or a filesystem lacking timestamp support can make
+    os.utime raise OSError; that is non-critical metadata, so the failure is
+    swallowed to keep attribute preservation best-effort.
+    """
+    try:
+        os.utime(dest, ns=(source_stat.st_atime_ns, source_stat.st_mtime_ns))
+    except OSError:
+        pass
+
+
 def _copy_extended_attributes(source: Path, dest: Path) -> None:
     """Copy extended attributes from source to dest if supported by OS."""
     if not all(hasattr(os, attr) for attr in ("listxattr", "getxattr", "setxattr")):

tests/test_media_shrinker.py

@@ -1914,3 +1914,32 @@ class MockStat:
                 with patch("media_shrinker._copy_macos_creation_time"):
                     with patch("media_shrinker._get_setfile_path", return_value="/bin/echo"):
                         preserve_file_attributes(src, dest)
+
+    def test_preserve_file_attributes_ignores_utime_error(self) -> None:
+        """os.utime failure must not abort best-effort metadata copy.
+
+        A read-only or timestamp-unsupporting destination filesystem can make
+        os.utime raise OSError. The documented contract is best-effort, so the
+        completed conversion must not be lost and the macOS creation-time step
+        must still run.
+        """
+        from media_shrinker import preserve_file_attributes
+
+        with tempfile.TemporaryDirectory() as tmp:
+            src = Path(tmp) / "src.txt"
+            src.write_text("hello")
+            dest = Path(tmp) / "dest.txt"
+            dest.write_text("world")
+            with patch(
+                "media_shrinker.os.utime", side_effect=OSError("read-only fs")
+            ):
+                with patch(
+                    "media_shrinker._copy_macos_creation_time"
+                ) as mock_creation:
+                    with patch(
+                        "media_shrinker._get_setfile_path", return_value="/bin/echo"
+                    ):
+                        # Must not raise despite os.utime failing.
+                        preserve_file_attributes(src, dest)
+            # Best-effort continues to the creation-time step after utime fails.
+            mock_creation.assert_called_once()