#11767: use context manager to close file in __getitem__ to prevent FD leak

All of the other methods in mailbox that create message objects take care to
close the file descriptors they use, so it seems to make sense to have
__getitem__ do so as well.

Patch by Filip Gruszczyński.

3 files changed, 37 insertions, 2 deletions

diff --git a/Lib/mailbox.py b/Lib/mailbox.py
index 0e4f99b..b96b270 100644
--- a/Lib/mailbox.py
+++ b/Lib/mailbox.py
@@ -20,6 +20,7 @@ import email
 import email.message
 import email.generator
 import io
+import contextlib
 try:
     if sys.platform == 'os2emx':
         # OS/2 EMX fcntl() not adequate
@@ -76,7 +77,8 @@ class Mailbox:
         if not self._factory:
             return self.get_message(key)
         else:
-            return self._factory(self.get_file(key))
+            with contextlib.closing(self.get_file(key)) as file:
+                return self._factory(file)
 
     def get_message(self, key):
         """Return a Message representation or raise a KeyError."""
diff --git a/Lib/test/test_mailbox.py b/Lib/test/test_mailbox.py
index 8dc7326..10317c3 100644
--- a/Lib/test/test_mailbox.py
+++ b/Lib/test/test_mailbox.py
@@ -1201,6 +1201,37 @@ class TestBabyl(TestMailbox):
         self.assertEqual(set(self._box.get_labels()), set(['blah']))
 
 
+class FakeFileLikeObject:
+
+    def __init__(self):
+        self.closed = False
+
+    def close(self):
+        self.closed = True
+
+
+class FakeMailBox(mailbox.Mailbox):
+
+    def __init__(self):
+        mailbox.Mailbox.__init__(self, '', lambda file: None)
+        self.files = [FakeFileLikeObject() for i in range(10)]
+
+    def get_file(self, key):
+        return self.files[key]
+
+
+class TestFakeMailBox(unittest.TestCase):
+
+    def test_closing_fd(self):
+        box = FakeMailBox()
+        for i in range(10):
+            self.assertFalse(box.files[i].closed)
+        for i in range(10):
+            box[i]
+        for i in range(10):
+            self.assertTrue(box.files[i].closed)
+
+
 class TestMessage(TestBase):
 
     _factory = mailbox.Message      # Overridden by subclasses to reuse tests
@@ -2113,7 +2144,7 @@ def test_main():
              TestBabyl, TestMessage, TestMaildirMessage, TestMboxMessage,
              TestMHMessage, TestBabylMessage, TestMMDFMessage,
              TestMessageConversion, TestProxyFile, TestPartialFile,
-             MaildirTestCase)
+             MaildirTestCase, TestFakeMailBox)
     support.run_unittest(*tests)
     support.reap_children()
 
diff --git a/Misc/NEWS b/Misc/NEWS
index 6cc0f03..ec8b72e 100644
--- a/Misc/NEWS
+++ b/Misc/NEWS
@@ -25,6 +25,8 @@ Core and Builtins
 Library
 -------
 
+- Issue #11767: Correct file descriptor leak in mailbox's __getitem__ method.
+
 - Issue #12133: AbstractHTTPHandler.do_open() of urllib.request closes the HTTP
   connection if its getresponse() method fails with a socket error. Patch
   written by Ezio Melotti.