Fix incomplete writes after close in asyncio._SelectorSocketTransport

Change introduced in gh-106503 cause the transport to miss writes
scheduled after it is closed.

Signed-off-by: Vojtěch Boček <vbocek@gmail.com>

Author: Tasssadar

Lib/asyncio/selector_events.py

@@ -1182,6 +1182,7 @@ def can_write_eof(self):
 
     def _call_connection_lost(self, exc):
         super()._call_connection_lost(exc)
+        self._write_ready = None
         if self._empty_waiter is not None:
             self._empty_waiter.set_exception(
                 ConnectionError("Connection is closed by peer"))
@@ -1199,7 +1200,6 @@ def _reset_empty_waiter(self):
 
     def close(self):
         self._read_ready_cb = None
-        self._write_ready = None
         super().close()
 
 

Lib/test/test_asyncio/test_selector_events.py

@@ -1026,6 +1026,45 @@ def test_transport_close_remove_writer(self, m_log):
         transport.close()
         remove_writer.assert_called_with(self.sock_fd)
 
+    def test_write_buffer_after_close(self):
+        # If the transport is closed while:
+        #  * Transport write buffer is not empty
+        #  * Transport is paused
+        #  * Protocol has data in its buffer, like SSLProtocol in self._outgoing
+        # The data is still written out.
+
+        data = memoryview(b'data')
+        self.sock.send.return_value = 2
+        self.sock.send.fileno.return_value = 7
+
+        def _resume_writing():
+            transport.write(b"data")
+            self.protocol.resume_writing.side_effect = None
+
+        self.protocol.resume_writing.side_effect = _resume_writing
+
+        transport = self.socket_transport()
+        transport._high_water = 1
+
+        transport.write(data)
+
+        self.assertTrue(transport._protocol_paused)
+        self.assertTrue(self.sock.send.called)
+        self.loop.assert_writer(7, transport._write_ready)
+
+        transport.close()
+
+        # not called, we still have data in write buffer
+        self.assertFalse(self.protocol.connection_lost.called)
+
+        self.loop.writers[7]._run()
+        # during this ^ run, the _resume_writing mock above was called and added more data
+
+        self.assertEqual(transport.get_write_buffer_size(), 2)
+        self.loop.writers[7]._run()
+
+        self.assertEqual(transport.get_write_buffer_size(), 0)
+        self.assertTrue(self.protocol.connection_lost.called)
 
 class SelectorSocketTransportBufferedProtocolTests(test_utils.TestCase):
 

Misc/ACKS

@@ -189,6 +189,7 @@ Stéphane Blondon
 Eric Blossom
 Sergey Bobrov
 Finn Bock
+Vojtěch Boček
 Paul Boddie
 Matthew Boedicker
 Robin Boerdijk

Misc/NEWS.d/next/Library/2024-12-17-16-48-02.gh-issue-115514.1yOJ7T.rst

@@ -0,0 +1,3 @@
+Fix exceptions and incomplete writes after asyncio _SelectorTransport
+is closed before writes are completed.
+Breaking change introduced in gh-106503, released in 3.12.0.