Rework radar system

python_app/tests/test_file_io.py

@@ -1,13 +1,17 @@
 """Settings commits retain valid files on failure and concurrent writes."""
 
 from concurrent.futures import ThreadPoolExecutor
+import ctypes
+import errno
 import json
+import os
 from pathlib import Path
+import stat
 import tempfile
 import unittest
 from unittest import mock
 
-from python_app.file_io import atomic_write_json
+from python_app.file_io import atomic_write_json, rename_no_replace
 from python_app.orchestration.gui_session_state import GuiSessionStateStore
 
 
@@ -32,6 +36,51 @@ class AtomicJsonTest(unittest.TestCase):
             atomic_write_json(self.path, {'bad': float('nan')})
         self.assertEqual(json.loads(self.path.read_text()), {'old': True})
 
+    def test_replacement_preserves_existing_permissions(self) -> None:
+        self.path.chmod(0o664)
+        atomic_write_json(self.path, {"new": True}, durable=True)
+        self.assertEqual(stat.S_IMODE(self.path.stat().st_mode), 0o664)
+
+    def test_new_file_uses_process_umask(self) -> None:
+        path = self.path.with_name("new.json")
+        previous = os.umask(0o027)
+        try:
+            atomic_write_json(path, {"new": True})
+        finally:
+            os.umask(previous)
+        self.assertEqual(stat.S_IMODE(path.stat().st_mode), 0o640)
+
+    def test_publish_cannot_replace_existing_file_or_empty_directory(self) -> None:
+        source = self.path.with_name('source')
+        source.write_text('new', encoding='utf-8')
+        before = self.path.read_bytes()
+        with self.assertRaises(FileExistsError):
+            rename_no_replace(source, self.path)
+        self.assertEqual(self.path.read_bytes(), before)
+        self.assertEqual(source.read_text(), 'new')
+        source.unlink()
+        source.mkdir()
+        destination = self.path.with_name('destination')
+        destination.mkdir()
+        with self.assertRaises(FileExistsError):
+            rename_no_replace(source, destination)
+        self.assertTrue(source.is_dir())
+        self.assertTrue(destination.is_dir())
+
+    def test_publish_propagates_filesystem_permission_error_without_touching_source(self) -> None:
+        destination = self.path.with_name('denied.json')
+
+        def deny(*_args):
+            ctypes.set_errno(errno.EACCES)
+            return -1
+
+        before = self.path.read_bytes()
+        with mock.patch('python_app.file_io._renameat2', side_effect=deny):
+            with self.assertRaises(PermissionError):
+                rename_no_replace(self.path, destination)
+        self.assertEqual(self.path.read_bytes(), before)
+        self.assertFalse(destination.exists())
+
     def test_concurrent_writers_publish_complete_json_and_leave_no_temp_files(self) -> None:
         payloads = [{'index': i, 'values': [i] * 1000} for i in range(32)]
         with ThreadPoolExecutor(max_workers=8) as executor: