Add a test for unclosed socket

bd3c98d44ce1da5f5edfe9120eec0c0ce4262c43
commit bd3c98d44ce1da5f5edfe9120eec0c0ce4262c43
diff --git a/Lib/test/test_urllib2net.py b/Lib/test/test_urllib2net.py
@@ -1,9 +1,12 @@
+import contextlib
 import errno
 import unittest
+from unittest import mock
 from test import support
 from test.support import os_helper
 from test.support import socket_helper
 from test.support import ResourceDenied
+from test.support.warnings_helper import check_no_resource_warning
 
 import os
 import socket
@@ -143,6 +146,36 @@ def test_ftp(self):
             ]
         self._test_urls(urls, self._extra_handlers())
 
+    def test_ftp_no_leak(self):
+        # gh-140691: When the data connection (but not control connection)
+        # cannot be made established, we shouldn't leave an open socket object.
+
+        class MockError(OSError):
+            pass
+
+        orig_create_connection = socket.create_connection
+        def patched_create_connection(address, *args, **kwargs):
+            """Simulate REJECTing connections to ports other than 21"""
+            host, port = address
+            if port != 21:
+                raise MockError()
+            return orig_create_connection(address, *args, **kwargs)
+
+        url = 'ftp://www.pythontest.net/README'
+        entry = url, None, urllib.error.URLError
+        no_cache_handlers = [urllib.request.FTPHandler()]
+        cache_handlers = self._extra_handlers()
+        with mock.patch('socket.create_connection', patched_create_connection):
+            with check_no_resource_warning(self):
+                # Try without CacheFTPHandler
+                self._test_urls([entry], handlers=no_cache_handlers)
+            with check_no_resource_warning(self):
+                # Try with CacheFTPHandler (uncached & cached)
+                self._test_urls([entry, entry], cache_handlers)
+        # Try without the mock: the handler should not use a closed connection
+        with check_no_resource_warning(self):
+            self._test_urls([url], cache_handlers)
+
     def test_file(self):
         TESTFN = os_helper.TESTFN
         f = open(TESTFN, 'w')
@@ -234,18 +267,16 @@ def _test_urls(self, urls, handlers, retry=True):
                 else:
                     req = expected_err = None
 
+                if expected_err:
+                    context = self.assertRaises(expected_err)
+                else:
+                    context = contextlib.nullcontext()
+
                 with socket_helper.transient_internet(url):
-                    try:
+                    f = None
+                    with context:
                         f = urlopen(url, req, support.INTERNET_TIMEOUT)
-                    # urllib.error.URLError is a subclass of OSError
-                    except OSError as err:
-                        if expected_err:
-                            msg = ("Didn't get expected error(s) %s for %s %s, got %s: %s" %
-                                   (expected_err, url, req, type(err), err))
-                            self.assertIsInstance(err, expected_err, msg)
-                        else:
-                            raise
-                    else:
+                    if f is not None:
                         try:
                             with time_out, \
                                  socket_peer_reset, \