#5346: Preserve permissions of mbox, MMDF and Babyl mailbox files on flush()

Lib/mailbox.py

@@ -691,6 +691,9 @@ class _singlefileMailbox(Mailbox):
         _sync_close(new_file)
         # self._file is about to get replaced, so no need to sync.
         self._file.close()
+        # Make sure the new file's mode is the same as the old file's
+        mode = os.stat(self._path).st_mode
+        os.chmod(new_file.name, mode)
         try:
             os.rename(new_file.name, self._path)
         except OSError as e:

Lib/test/test_mailbox.py

@@ -966,6 +966,23 @@ class _TestSingleFile(TestMailbox):
         self._box = self._factory(self._path)
         self.assertEqual(len(self._box), 1)
 
+    def test_permissions_after_flush(self):
+        # See issue #5346
+
+        # Make the mailbox world writable. It's unlikely that the new
+        # mailbox file would have these permissions after flush(),
+        # because umask usually prevents it.
+        mode = os.stat(self._path).st_mode | 0o666
+        os.chmod(self._path, mode)
+
+        self._box.add(self._template % 0)
+        i = self._box.add(self._template % 1)
+        # Need to remove one message to make flush() create a new file
+        self._box.remove(i)
+        self._box.flush()
+
+        self.assertEqual(os.stat(self._path).st_mode, mode)
+
 
 class _TestMboxMMDF(_TestSingleFile):
 

Misc/NEWS

@@ -81,6 +81,9 @@ Core and Builtins
 Library
 -------
 
+- Issue #5346: Preserve permissions of mbox, MMDF and Babyl mailbox
+  files on flush().
+
 - Issue #10571: Fix the "--sign" option of distutils' upload command.
   Patch by Jakub Wilk.