gh-156400: Close the socket or pipe when transport creation fails in asyncio datagram/pipe endpoints

[tonghuaroot]

create_datagram_endpoint(), connect_read_pipe() and connect_write_pipe() create or take ownership of a socket/pipe and then run protocol_factory() and transport creation. The only cleanup (except: transport.close()) covers await waiter, so if protocol_factory() or _make_*_transport() raises the resource is never closed and leaks until garbage collection.

Close the socket/pipe on that path, matching the create_connection() fix in gh-153133. The added regression tests fail without the fix and pass with it; the full test_asyncio suite passes.

• Issue: asyncio leaks the socket/pipe in create_datagram_endpoint and connect_read_pipe/connect_write_pipe when transport creation fails #156400

[kumaraditya303]

CI is failing

[bedevere-app]

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[tonghuaroot]

Thanks — fixed. The Windows failure was test_windows_events.check_write_rejected: on the proactor, _make_write_pipe_transport() takes ownership of the pipe and starts IOCP I/O before it can raise (WinError 87), so closing the pipe in connect_write_pipe's except double-managed it (the half-built transport's __del__ then hit I/O operation on closed pipe).

I've narrowed all three methods to close the socket/pipe only when protocol_factory() raises — i.e. before any transport exists. Once _make_*_transport() is called the transport owns the resource and cleans up on failure itself. The added tests still pass and the Windows regression is gone.