gh-153133: Fix socket leak in asyncio create_connection

Author: deadlovelll

Lib/asyncio/base_events.py

@@ -1219,26 +1219,31 @@ async def _create_connection_transport(
             ssl_handshake_timeout=None,
             ssl_shutdown_timeout=None, context=None):
 
-        sock.setblocking(False)
-        context = context if context is not None else contextvars.copy_context()
-
-        protocol = protocol_factory()
-        waiter = self.create_future()
-        if ssl:
-            sslcontext = None if isinstance(ssl, bool) else ssl
-            transport = self._make_ssl_transport(
-                sock, protocol, sslcontext, waiter,
-                server_side=server_side, server_hostname=server_hostname,
-                ssl_handshake_timeout=ssl_handshake_timeout,
-                ssl_shutdown_timeout=ssl_shutdown_timeout,
-                context=context)
-        else:
-            transport = self._make_socket_transport(sock, protocol, waiter, context=context)
-
+        # gh-153133: close the socket if the transport is never created.
+        transport = None
         try:
+            sock.setblocking(False)
+            context = context if context is not None else contextvars.copy_context()
+
+            protocol = protocol_factory()
+            waiter = self.create_future()
+            if ssl:
+                sslcontext = None if isinstance(ssl, bool) else ssl
+                transport = self._make_ssl_transport(
+                    sock, protocol, sslcontext, waiter,
+                    server_side=server_side, server_hostname=server_hostname,
+                    ssl_handshake_timeout=ssl_handshake_timeout,
+                    ssl_shutdown_timeout=ssl_shutdown_timeout,
+                    context=context)
+            else:
+                transport = self._make_socket_transport(sock, protocol, waiter, context=context)
+
             await waiter
         except:
-            transport.close()
+            if transport is None:
+                sock.close()
+            else:
+                transport.close()
             raise
 
         return transport, protocol

Lib/test/test_asyncio/test_base_events.py

@@ -1282,6 +1282,47 @@ def getaddrinfo(*args, **kw):
                 self.loop.run_until_complete(coro)
             self.assertTrue(sock.close.called)
 
+    def test_create_connection_sock_transport_error_closes_sock(self):
+        # gh-153133: a user-provided socket is closed if the transport is
+        # never created.
+        sock = mock.Mock()
+        sock.type = socket.SOCK_STREAM
+
+        def factory():
+            raise ZeroDivisionError
+
+        coro = self.loop.create_connection(factory, sock=sock)
+        with self.assertRaises(ZeroDivisionError):
+            self.loop.run_until_complete(coro)
+        self.assertTrue(sock.close.called)
+
+    @patch_socket
+    def test_create_connection_transport_error_closes_sock(self, m_socket):
+        # gh-153133: an internally created socket is closed if the transport
+        # is never created.
+        sock = mock.Mock()
+        m_socket.socket.return_value = sock
+
+        def getaddrinfo(*args, **kw):
+            fut = self.loop.create_future()
+            addr = (socket.AF_INET, socket.SOCK_STREAM, 0, '',
+                    ('127.0.0.1', 80))
+            fut.set_result([addr])
+            return fut
+        self.loop.getaddrinfo = getaddrinfo
+
+        async def sock_connect(sock, address):
+            return None
+
+        def factory():
+            raise ZeroDivisionError
+
+        with mock.patch.object(self.loop, 'sock_connect', sock_connect):
+            coro = self.loop.create_connection(factory, '127.0.0.1', 80)
+            with self.assertRaises(ZeroDivisionError):
+                self.loop.run_until_complete(coro)
+        self.assertTrue(sock.close.called)
+
     @patch_socket
     def test_create_connection_happy_eyeballs_empty_exceptions(self, m_socket):
         # See gh-135836: Fix IndexError when Happy Eyeballs algorithm

Misc/NEWS.d/next/Library/2026-07-05-17-39-16.gh-issue-153133.kKSH7g.rst

@@ -0,0 +1,2 @@
+Fix a socket leak in :meth:`asyncio.loop.create_connection` when the
+transport cannot be created.