[3.15] gh-156512: Fix asyncio calling connection_lost() twice from resume_writing() (GH-156657) by miss-islington · Pull Request #157031 · python/cpython · GitHub
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[3.15] gh-156512: Fix asyncio calling connection_lost() twice from resume_writing() (GH-156657) #157031

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[3.15] gh-156512: Fix asyncio calling connection_lost() twice from resume_writing() (GH-156657) #157031

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8 changes: 6 additions & 2 deletions Lib/asyncio/selector_events.py
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43 changes: 43 additions & 0 deletions Lib/test/test_asyncio/test_selector_events.py
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Original file line number Diff line number Diff line change
Expand Up @@ -1122,6 +1122,49 @@ def _resume_writing():
self.assertEqual(transport.get_write_buffer_size(), 0)
self.assertTrue(self.protocol.connection_lost.called)

def test_write_ready_resume_writing_closes(self):
# gh-156512: closing from resume_writing() must not lose the connection twice
self.sock.send.return_value = 2

def _resume_writing():
transport.close()

self.protocol.resume_writing.side_effect = _resume_writing
self.loop.call_exception_handler = mock.Mock()

transport = self.socket_transport()
transport.set_write_buffer_limits(high=1, low=0)
transport.write(b'data')

self.loop.writers[7]._run()
test_utils.run_briefly(self.loop)

self.assertEqual(self.protocol.connection_lost.call_count, 1)
self.loop.call_exception_handler.assert_not_called()

@unittest.skipUnless(selector_events._HAS_SENDMSG, 'no sendmsg')
def test_write_sendmsg_resume_writing_closes(self):
# gh-156512: same as above, for the sendmsg write path
self.sock.send.return_value = 2
self.sock.sendmsg.return_value = 2

def _resume_writing():
transport.close()

self.protocol.resume_writing.side_effect = _resume_writing
self.loop.call_exception_handler = mock.Mock()

transport = self.socket_transport(sendmsg=True)
transport.set_write_buffer_limits(high=1, low=0)
transport.write(b'data')

self.loop.writers[7]._run()
test_utils.run_briefly(self.loop)

self.assertEqual(self.protocol.connection_lost.call_count, 1)
self.loop.call_exception_handler.assert_not_called()


class SelectorSocketTransportBufferedProtocolTests(test_utils.TestCase):

def setUp(self):
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2 changes: 2 additions & 0 deletions Misc/NEWS.d/next/Library/2026-08-30-13-25-53.gh-issue-156512.tVTOIV.rst
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