bpo-36801: Fix waiting in StreamWriter.drain for closing SSL transport (GH-13098)


https://bugs.python.org/issue36801
(cherry picked from commit 1cc0ee7d9f6a2817918fafd24c18d8bb093a85d3)

Co-authored-by: Andrew Svetlov <andrew.svetlov@gmail.com>
diff --git a/Lib/asyncio/streams.py b/Lib/asyncio/streams.py
index d6531f8..50badd6 100644
--- a/Lib/asyncio/streams.py
+++ b/Lib/asyncio/streams.py
@@ -208,6 +208,9 @@
         self._drain_waiter = waiter
         await waiter
 
+    def _get_close_waiter(self, stream):
+        raise NotImplementedError
+
 
 class StreamReaderProtocol(FlowControlMixin, protocols.Protocol):
     """Helper class to adapt between Protocol and StreamReader.
@@ -265,6 +268,9 @@
             return False
         return True
 
+    def _get_close_waiter(self, stream):
+        return self._closed
+
     def __del__(self):
         # Prevent reports about unhandled exceptions.
         # Better than self._closed._log_traceback = False hack
@@ -320,7 +326,7 @@
         return self._transport.is_closing()
 
     async def wait_closed(self):
-        await self._protocol._closed
+        await self._protocol._get_close_waiter(self)
 
     def get_extra_info(self, name, default=None):
         return self._transport.get_extra_info(name, default)
@@ -338,13 +344,12 @@
             if exc is not None:
                 raise exc
         if self._transport.is_closing():
-            # Yield to the event loop so connection_lost() may be
-            # called.  Without this, _drain_helper() would return
-            # immediately, and code that calls
-            #     write(...); await drain()
-            # in a loop would never call connection_lost(), so it
-            # would not see an error when the socket is closed.
-            await sleep(0, loop=self._loop)
+            # Wait for protocol.connection_lost() call
+            # Raise connection closing error if any,
+            # ConnectionResetError otherwise
+            fut = self._protocol._get_close_waiter(self)
+            await fut
+            raise ConnectionResetError('Connection lost')
         await self._protocol._drain_helper()