Issue #22351: The nntplib.NNTP constructor no longer leaves the connection

and socket open until the garbage collector cleans them up.  Patch by
Martin Panter.

Lib/nntplib.py

@@ -1041,11 +1041,18 @@ class NNTP(_NNTPBase):
         self.host = host
         self.port = port
         self.sock = socket.create_connection((host, port), timeout)
-        file = self.sock.makefile("rwb")
-        _NNTPBase.__init__(self, file, host,
-                           readermode, timeout)
-        if user or usenetrc:
-            self.login(user, password, usenetrc)
+        file = None
+        try:
+            file = self.sock.makefile("rwb")
+            _NNTPBase.__init__(self, file, host,
+                               readermode, timeout)
+            if user or usenetrc:
+                self.login(user, password, usenetrc)
+        except:
+            if file:
+                file.close()
+            self.sock.close()
+            raise
 
     def _close(self):
         try:
@@ -1065,12 +1072,19 @@ if _have_ssl:
             in default port and the `ssl_context` argument for SSL connections.
             """
             self.sock = socket.create_connection((host, port), timeout)
-            self.sock = _encrypt_on(self.sock, ssl_context, host)
-            file = self.sock.makefile("rwb")
-            _NNTPBase.__init__(self, file, host,
-                               readermode=readermode, timeout=timeout)
-            if user or usenetrc:
-                self.login(user, password, usenetrc)
+            file = None
+            try:
+                self.sock = _encrypt_on(self.sock, ssl_context, host)
+                file = self.sock.makefile("rwb")
+                _NNTPBase.__init__(self, file, host,
+                                   readermode=readermode, timeout=timeout)
+                if user or usenetrc:
+                    self.login(user, password, usenetrc)
+            except:
+                if file:
+                    file.close()
+                self.sock.close()
+                raise
 
         def _close(self):
             try:

Lib/test/test_nntplib.py

@@ -8,6 +8,7 @@ import contextlib
 from test import support
 from nntplib import NNTP, GroupInfo
 import nntplib
+from unittest.mock import patch
 try:
     import ssl
 except ImportError:
@@ -370,6 +371,14 @@ class _NNTPServerIO(io.RawIOBase):
         return n
 
 
+def make_mock_file(handler):
+    sio = _NNTPServerIO(handler)
+    # Using BufferedRWPair instead of BufferedRandom ensures the file
+    # isn't seekable.
+    file = io.BufferedRWPair(sio, sio)
+    return (sio, file)
+
+
 class MockedNNTPTestsMixin:
     # Override in derived classes
     handler_class = None
@@ -384,10 +393,7 @@ class MockedNNTPTestsMixin:
 
     def make_server(self, *args, **kwargs):
         self.handler = self.handler_class()
-        self.sio = _NNTPServerIO(self.handler)
-        # Using BufferedRWPair instead of BufferedRandom ensures the file
-        # isn't seekable.
-        file = io.BufferedRWPair(self.sio, self.sio)
+        self.sio, file = make_mock_file(self.handler)
         self.server = nntplib._NNTPBase(file, 'test.server', *args, **kwargs)
         return self.server
 
@@ -1425,5 +1431,93 @@ class PublicAPITests(unittest.TestCase):
             target_api.append('NNTP_SSL')
         self.assertEqual(set(nntplib.__all__), set(target_api))
 
+class MockSocketTests(unittest.TestCase):
+    """Tests involving a mock socket object
+
+    Used where the _NNTPServerIO file object is not enough."""
+
+    nntp_class = nntplib.NNTP
+
+    def check_constructor_error_conditions(
+            self, handler_class,
+            expected_error_type, expected_error_msg,
+            login=None, password=None):
+
+        class mock_socket_module:
+            def create_connection(address, timeout):
+                return MockSocket()
+
+        class MockSocket:
+            def close(self):
+                nonlocal socket_closed
+                socket_closed = True
+
+            def makefile(socket, mode):
+                handler = handler_class()
+                _, file = make_mock_file(handler)
+                files.append(file)
+                return file
+
+        socket_closed = False
+        files = []
+        with patch('nntplib.socket', mock_socket_module), \
+             self.assertRaisesRegex(expected_error_type, expected_error_msg):
+            self.nntp_class('dummy', user=login, password=password)
+        self.assertTrue(socket_closed)
+        for f in files:
+            self.assertTrue(f.closed)
+
+    def test_bad_welcome(self):
+        #Test a bad welcome message
+        class Handler(NNTPv1Handler):
+            welcome = 'Bad Welcome'
+        self.check_constructor_error_conditions(
+            Handler, nntplib.NNTPProtocolError, Handler.welcome)
+
+    def test_service_temporarily_unavailable(self):
+        #Test service temporarily unavailable
+        class Handler(NNTPv1Handler):
+            welcome = '400 Service temporarily unavilable'
+        self.check_constructor_error_conditions(
+            Handler, nntplib.NNTPTemporaryError, Handler.welcome)
+
+    def test_service_permanently_unavailable(self):
+        #Test service permanently unavailable
+        class Handler(NNTPv1Handler):
+            welcome = '502 Service permanently unavilable'
+        self.check_constructor_error_conditions(
+            Handler, nntplib.NNTPPermanentError, Handler.welcome)
+
+    def test_bad_capabilities(self):
+        #Test a bad capabilities response
+        class Handler(NNTPv1Handler):
+            def handle_CAPABILITIES(self):
+                self.push_lit(capabilities_response)
+        capabilities_response = '201 bad capability'
+        self.check_constructor_error_conditions(
+            Handler, nntplib.NNTPReplyError, capabilities_response)
+
+    def test_login_aborted(self):
+        #Test a bad authinfo response
+        login = 't@e.com'
+        password = 'python'
+        class Handler(NNTPv1Handler):
+            def handle_AUTHINFO(self, *args):
+                self.push_lit(authinfo_response)
+        authinfo_response = '503 Mechanism not recognized'
+        self.check_constructor_error_conditions(
+            Handler, nntplib.NNTPPermanentError, authinfo_response,
+            login, password)
+
+@unittest.skipUnless(ssl, 'requires SSL support')
+class MockSslTests(MockSocketTests):
+    class nntp_class(nntplib.NNTP_SSL):
+        def __init__(self, *pos, **kw):
+            class bypass_context:
+                """Bypass encryption and actual SSL module"""
+                def wrap_socket(sock, **args):
+                    return sock
+            return super().__init__(*pos, ssl_context=bypass_context, **kw)
+
 if __name__ == "__main__":
     unittest.main()

Misc/NEWS

@@ -18,6 +18,10 @@ Core and Builtins
 Library
 -------
 
+- Issue #22351: The nntplib.NNTP constructor no longer leaves the connection
+  and socket open until the garbage collector cleans them up.  Patch by
+  Martin Panter.
+
 - Issue #23136: _strptime now uniformly handles all days in week 0, including
   Dec 30 of previous year.  Based on patch by Jim Carroll.