gh-160429: Always close the socket in proactor _call_connection_lost()

Lib/asyncio/proactor_events.py

@@ -159,19 +159,27 @@ def _call_connection_lost(self, exc):
         try:
             self._protocol.connection_lost(exc)
         finally:
-            # XXX If there is a pending overlapped read on the other
-            # end then it may fail with ERROR_NETNAME_DELETED if we
-            # just close our end.  First calling shutdown() seems to
-            # cure it, but maybe using DisconnectEx() would be better.
-            if hasattr(self._sock, 'shutdown') and self._sock.fileno() != -1:
-                self._sock.shutdown(socket.SHUT_RDWR)
-            self._sock.close()
-            self._sock = None
-            server = self._server
-            if server is not None:
-                server._detach(self)
-                self._server = None
-            self._called_connection_lost = True
+            try:
+                # XXX If there is a pending overlapped read on the other
+                # end then it may fail with ERROR_NETNAME_DELETED if we
+                # just close our end.  First calling shutdown() seems to
+                # cure it, but maybe using DisconnectEx() would be better.
+                if (hasattr(self._sock, 'shutdown')
+                        and self._sock.fileno() != -1):
+                    try:
+                        self._sock.shutdown(socket.SHUT_RDWR)
+                    except ConnectionError:
+                        # The peer has already reset the connection.
+                        pass
+            finally:
+                # Always release the socket, even if shutdown() failed.
+                self._sock.close()
+                self._sock = None
+                server = self._server
+                if server is not None:
+                    server._detach(self)
+                    self._server = None
+                self._called_connection_lost = True
 
     def get_write_buffer_size(self):
         size = self._pending_write

Lib/test/test_asyncio/test_proactor_events.py

@@ -336,6 +336,36 @@ def test_call_connection_lost(self):
         self.assertTrue(self.protocol.connection_lost.called)
         self.assertTrue(self.sock.close.called)
 
+    def test_call_connection_lost_shutdown_reset(self):
+        # gh-160429: a connection reset by the peer must not prevent
+        # the socket from being closed and the transport from being
+        # detached from its server.
+        server = mock.Mock()
+        tr = _ProactorSocketTransport(self.loop, self.sock, self.protocol,
+                                      server=server)
+        self.sock.shutdown.side_effect = ConnectionResetError
+        tr._call_connection_lost(None)
+        self.protocol.connection_lost.assert_called_once_with(None)
+        self.sock.shutdown.assert_called_once_with(socket.SHUT_RDWR)
+        self.sock.close.assert_called_once_with()
+        server._detach.assert_called_once_with(tr)
+        self.assertIsNone(tr._sock)
+        self.assertIsNone(tr._server)
+        self.assertTrue(tr._called_connection_lost)
+
+    def test_call_connection_lost_shutdown_error(self):
+        # Unexpected shutdown() errors still propagate, but the socket is
+        # closed anyway.
+        server = mock.Mock()
+        tr = _ProactorSocketTransport(self.loop, self.sock, self.protocol,
+                                      server=server)
+        self.sock.shutdown.side_effect = OSError
+        with self.assertRaises(OSError):
+            tr._call_connection_lost(None)
+        self.sock.close.assert_called_once_with()
+        server._detach.assert_called_once_with(tr)
+        self.assertTrue(tr._called_connection_lost)
+
     def test_write_eof(self):
         tr = self.socket_transport()
         self.assertTrue(tr.can_write_eof())

Misc/NEWS.d/next/Library/2026-10-24-15-30-00.gh-issue-160429.Rk3vQd.rst

@@ -0,0 +1,3 @@
+Fix :mod:`asyncio` proactor transports skipping the closing of the socket
+and the detaching from the server when the socket shutdown fails because
+the peer has already reset the connection.