gh-114914: Avoid keeping dead StreamWriter alive

Lib/asyncio/streams.py

@@ -201,7 +201,6 @@ def __init__(self, stream_reader, client_connected_cb=None, loop=None):
             # is established.
             self._strong_reader = stream_reader
         self._reject_connection = False
-        self._stream_writer = None
         self._task = None
         self._transport = None
         self._client_connected_cb = client_connected_cb
@@ -214,10 +213,8 @@ def _stream_reader(self):
             return None
         return self._stream_reader_wr()
 
-    def _replace_writer(self, writer):
+    def _replace_transport(self, transport):
         loop = self._loop
-        transport = writer.transport
-        self._stream_writer = writer
         self._transport = transport
         self._over_ssl = transport.get_extra_info('sslcontext') is not None
 
@@ -239,11 +236,8 @@ def connection_made(self, transport):
             reader.set_transport(transport)
         self._over_ssl = transport.get_extra_info('sslcontext') is not None
         if self._client_connected_cb is not None:
-            self._stream_writer = StreamWriter(transport, self,
-                                               reader,
-                                               self._loop)
-            res = self._client_connected_cb(reader,
-                                            self._stream_writer)
+            writer = StreamWriter(transport, self, reader, self._loop)
+            res = self._client_connected_cb(reader, writer)
             if coroutines.iscoroutine(res):
                 def callback(task):
                     if task.cancelled():
@@ -405,7 +399,7 @@ async def start_tls(self, sslcontext, *,
             ssl_handshake_timeout=ssl_handshake_timeout,
             ssl_shutdown_timeout=ssl_shutdown_timeout)
         self._transport = new_transport
-        protocol._replace_writer(self)
+        protocol._replace_transport(new_transport)
 
     def __del__(self, warnings=warnings):
         if not self._transport.is_closing():

Lib/test/test_asyncio/test_streams.py

@@ -1129,6 +1129,31 @@ async def inner(httpd):
 
         self.assertEqual(messages, [])
 
+    def test_unclosed_server_resource_warnings(self):
+        async def inner(rd, wr):
+            fut.set_result(True)
+            with self.assertWarns(ResourceWarning) as cm:
+                del wr
+                gc.collect()
+                self.assertEqual(len(cm.warnings), 1)
+                self.assertTrue(str(cm.warnings[0].message).startswith("unclosed <StreamWriter"))
+
+        async def outer():
+            srv = await asyncio.start_server(inner, socket_helper.HOSTv4, 0)
+            async with srv:
+                addr = srv.sockets[0].getsockname()
+                with socket.create_connection(addr):
+                    # Give the loop some time to notice the connection
+                    await fut
+
+        messages = []
+        self.loop.set_exception_handler(lambda loop, ctx: messages.append(ctx))
+
+        fut = self.loop.create_future()
+        self.loop.run_until_complete(outer())
+
+        self.assertEqual(messages, [])
+
     def _basetest_unhandled_exceptions(self, handle_echo):
         port = socket_helper.find_unused_port()
 

Misc/NEWS.d/next/Library/2024-02-19-15-52-30.gh-issue-114914.M5-1d8.rst

@@ -0,0 +1,2 @@
+Fix an issue where an abandoned :class:`StreamWriter` would not be garbage
+collected.