pythongh-118950: Let _SSLProtocolTransport.is_closing reflect SSLProt…

…ocol internal transport closing state so that StreamWriter.drain will invoke sleep(0) which calls connection_lost and correctly notifies waiters of connection lost. (python#118950)

Lib/asyncio/sslproto.py

@@ -101,7 +101,7 @@ def get_protocol(self):
         return self._ssl_protocol._app_protocol
 
     def is_closing(self):
-        return self._closed
+        return self._closed or self._ssl_protocol._is_transport_closing()
 
     def close(self):
         """Close the transport.
@@ -379,6 +379,9 @@ def _get_app_transport(self):
             self._app_transport_created = True
         return self._app_transport
 
+    def _is_transport_closing(self):
+        return self._transport is not None and self._transport.is_closing()
+
     def connection_made(self, transport):
         """Called when the low-level connection is made.
 

Misc/NEWS.d/next/Core and Builtins/2024-05-12-03-10-36.gh-issue-118950.5Wc4vp.rst

@@ -0,0 +1,3 @@
+Let _SSLProtocolTransport.is_closing reflect SSLProtocol internal transport
+closing state so that StreamWriter.drain will invoke sleep(0) which calls
+connection_lost and correctly notifies waiters of connection lost.