bpo-31647: Fix write_eof() after close() for SelectorSocketTransport (GH-7149)

Fixed bug where calling write_eof() on a _SelectorSocketTransport after
it's already closed raises AttributeError.

Lib/asyncio/selector_events.py

@@ -899,7 +899,7 @@ class _SelectorSocketTransport(_SelectorTransport):
                     self._sock.shutdown(socket.SHUT_WR)
 
     def write_eof(self):
-        if self._eof:
+        if self._closing or self._eof:
             return
         self._eof = True
         if not self._buffer:

Lib/test/test_asyncio/test_selector_events.py

@@ -1263,6 +1263,12 @@ class SelectorSocketTransportTests(test_utils.TestCase):
         self.sock.shutdown.assert_called_with(socket.SHUT_WR)
         tr.close()
 
+    def test_write_eof_after_close(self):
+        tr = self.socket_transport()
+        tr.close()
+        self.loop.run_until_complete(asyncio.sleep(0))
+        tr.write_eof()
+
     @mock.patch('asyncio.base_events.logger')
     def test_transport_close_remove_writer(self, m_log):
         remove_writer = self.loop._remove_writer = mock.Mock()

Misc/NEWS.d/next/Library/2018-05-28-18-40-26.bpo-31467.s4Fad3.rst

+Fixed bug where calling write_eof() on a _SelectorSocketTransport after it's
+already closed raises AttributeError.