Fix FUSE copy fallback (#957)

Fixes #949

shelfmark/download/fs.py

@@ -229,6 +229,10 @@ def _is_permission_error(e: Exception) -> bool:
     return isinstance(e, PermissionError) or (isinstance(e, OSError) and e.errno == errno.EPERM)
 
 
+def _should_fallback_to_content_copy(error: Exception) -> bool:
+    return _is_permission_error(error) or (isinstance(error, OSError) and error.errno == errno.EIO)
+
+
 def _system_op(op: str, source: Path, dest: Path) -> None:
     """Execute system command (mv or cp) as final fallback."""
     logger.warning("Attempting system %s as final fallback: %s -> %s", op, source, dest)
@@ -463,9 +467,9 @@ def atomic_move(source_path: Path, dest_path: Path, max_attempts: int = 100) ->
                     try:
                         run_blocking_io(shutil.copy2, str(source_path), str(temp_path))
                     except (PermissionError, OSError) as copy_error:
-                        if _is_permission_error(copy_error):
+                        if _should_fallback_to_content_copy(copy_error):
                             logger.debug(
-                                "Permission error during move-copy, falling back to copyfile (%s -> %s): %s",
+                                "copy2 failed during move-copy, falling back to copyfile (%s -> %s): %s",
                                 source_path,
                                 temp_path,
                                 copy_error,
@@ -631,16 +635,16 @@ def atomic_copy(source_path: Path, dest_path: Path, max_attempts: int = 100) ->
             try:
                 run_blocking_io(shutil.copy2, str(source_path), str(temp_path))
             except (PermissionError, OSError) as e:
-                # Handle NFS permission errors immediately here
-                if _is_permission_error(e):
-                    log_transfer_permission_context(
-                        "atomic_copy",
-                        source=source_path,
-                        dest=temp_path,
-                        error=e,
-                    )
+                if _should_fallback_to_content_copy(e):
+                    if _is_permission_error(e):
+                        log_transfer_permission_context(
+                            "atomic_copy",
+                            source=source_path,
+                            dest=temp_path,
+                            error=e,
+                        )
                     logger.debug(
-                        "Permission error during copy, falling back to copyfile (%s -> %s): %s",
+                        "copy2 failed during copy, falling back to copyfile (%s -> %s): %s",
                         source_path,
                         temp_path,
                         e,

tests/core/test_download_processing.py

@@ -240,6 +240,26 @@ class TestAtomicCopy:
         assert result.exists()
         assert result.read_text() == "content"
 
+    def test_copy_falls_back_when_copy2_hits_fuse_eio(self, tmp_path):
+        """Fall back to content copy when FUSE rejects xattr metadata reads."""
+        import errno
+
+        from shelfmark.download.fs import atomic_copy as _atomic_copy
+
+        source = tmp_path / "source.txt"
+        source.write_text("content")
+        dest = tmp_path / "dest.txt"
+
+        with patch(
+            "shelfmark.download.fs.shutil.copy2",
+            side_effect=OSError(errno.EIO, "Input/output error"),
+        ):
+            result = _atomic_copy(source, dest)
+
+        assert result == dest
+        assert result.exists()
+        assert result.read_text() == "content"
+
     def test_copy_tolerates_post_publish_estale(self, tmp_path, monkeypatch):
         """Treat ESTALE on the final destination as a successful NFS publish."""
         import errno

tests/core/test_hardlink.py

@@ -407,6 +407,32 @@ class TestAtomicMove:
         assert mock_copy.called
         assert mock_fallback.called
 
+    def test_cross_filesystem_move_falls_back_when_copy2_hits_fuse_eio(self, tmp_path, monkeypatch):
+        """Falls back to content copy when FUSE rejects xattr metadata reads."""
+        import errno
+
+        from shelfmark.download.fs import atomic_move as _atomic_move
+
+        source = tmp_path / "source.txt"
+        source.write_text("content")
+        dest = tmp_path / "dest.txt"
+
+        def _raise_exdev(*_args, **_kwargs):
+            raise OSError(errno.EXDEV, "Cross-device link")
+
+        monkeypatch.setattr(os, "rename", _raise_exdev)
+
+        with patch(
+            "shelfmark.download.fs.shutil.copy2",
+            side_effect=OSError(errno.EIO, "Input/output error"),
+        ):
+            result = _atomic_move(source, dest)
+
+        assert result == dest
+        assert not source.exists()
+        assert dest.exists()
+        assert dest.read_text() == "content"
+
     def test_cross_filesystem_move_recovers_when_metadata_step_hits_enoent(
         self, tmp_path, monkeypatch
     ):