Inherit asyncio proactor datagram transport from asyncio.DatagramTransport (GH-31512)

(cherry picked from commit cff4d5c)

Co-authored-by: Andrew Svetlov <[email protected]>

Author: miss-islington

Lib/asyncio/proactor_events.py

@@ -450,7 +450,8 @@ def _pipe_closed(self, fut):
             self.close()
 
 
-class _ProactorDatagramTransport(_ProactorBasePipeTransport):
+class _ProactorDatagramTransport(_ProactorBasePipeTransport,
+                                 transports.DatagramTransport):
     max_size = 256 * 1024
     def __init__(self, loop, sock, protocol, address=None,
                  waiter=None, extra=None):

Lib/test/test_asyncio/test_proactor_events.py

@@ -823,6 +823,7 @@ def datagram_transport(self):
     def test_make_datagram_transport(self):
         tr = self.datagram_transport()
         self.assertIsInstance(tr, _ProactorDatagramTransport)
+        self.assertIsInstance(tr, asyncio.DatagramTransport)
         close_transport(tr)
 
     def test_datagram_loop_writing(self):

Misc/NEWS.d/next/Library/2022-02-23-00-55-59.bpo-44886.I40Mbr.rst

@@ -0,0 +1,2 @@
+Inherit asyncio proactor datagram transport from
+:class:`asyncio.DatagramTransport`.