https://github.com/python/cpython/commit/be5e65fdf67b1817e173e73443564c7c146b09a4
commit: be5e65fdf67b1817e173e73443564c7c146b09a4
branch: main
author: Serhiy Storchaka <storch...@gmail.com>
committer: serhiy-storchaka <storch...@gmail.com>
date: 2024-01-10T15:31:55+02:00
summary:

gh-66515: Fix locking of an MH mailbox without ".mh_sequences" file (GH-113482)

Guarantee that it either open an existing ".mh_sequences" file or create
a new ".mh_sequences" file, but do not replace existing ".mh_sequences"
file.

files:
M Lib/mailbox.py
M Lib/test/test_mailbox.py

diff --git a/Lib/mailbox.py b/Lib/mailbox.py
index 0e1d49b399d077..81ea210cf815a4 100644
--- a/Lib/mailbox.py
+++ b/Lib/mailbox.py
@@ -1141,10 +1141,24 @@ def __len__(self):
         """Return a count of messages in the mailbox."""
         return len(list(self.iterkeys()))
 
+    def _open_mh_sequences_file(self, text):
+        mode = '' if text else 'b'
+        kwargs = {'encoding': 'ASCII'} if text else {}
+        path = os.path.join(self._path, '.mh_sequences')
+        while True:
+            try:
+                return open(path, 'r+' + mode, **kwargs)
+            except FileNotFoundError:
+                pass
+            try:
+                return open(path, 'x+' + mode, **kwargs)
+            except FileExistsError:
+                pass
+
     def lock(self):
         """Lock the mailbox."""
         if not self._locked:
-            self._file = open(os.path.join(self._path, '.mh_sequences'), 'rb+')
+            self._file = self._open_mh_sequences_file(text=False)
             _lock_file(self._file)
             self._locked = True
 
@@ -1225,8 +1239,9 @@ def get_sequences(self):
 
     def set_sequences(self, sequences):
         """Set sequences using the given name-to-key-list dictionary."""
-        f = open(os.path.join(self._path, '.mh_sequences'), 'w', 
encoding='ASCII')
+        f = self._open_mh_sequences_file(text=True)
         try:
+            os.close(os.open(f.name, os.O_WRONLY | os.O_TRUNC))
             for name, keys in sequences.items():
                 if len(keys) == 0:
                     continue
diff --git a/Lib/test/test_mailbox.py b/Lib/test/test_mailbox.py
index 8c350eb02ccc17..d84faad0eb3406 100644
--- a/Lib/test/test_mailbox.py
+++ b/Lib/test/test_mailbox.py
@@ -1360,6 +1360,15 @@ def test_no_dot_mh_sequences_file(self):
         box.set_sequences({})
         self.assertEqual(os.listdir(path), ['.mh_sequences'])
 
+    def test_lock_unlock_no_dot_mh_sequences_file(self):
+        path = os.path.join(self._path, 'foo.bar')
+        os.mkdir(path)
+        box = self._factory(path)
+        self.assertEqual(os.listdir(path), [])
+        box.lock()
+        box.unlock()
+        self.assertEqual(os.listdir(path), ['.mh_sequences'])
+
     def test_issue2625(self):
         msg0 = mailbox.MHMessage(self._template % 0)
         msg0.add_sequence('foo')

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