Fix Windows subprocess NotImplementedError for STDIO clients #1009
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On Windows, asyncio.create_subprocess_exec raises NotImplementedError due to incomplete subprocess transport support in ProactorEventLoop. This commit implements a fallback using subprocess.Popen directly with async wrappers. The fix introduces a DummyProcess class that wraps subprocess.Popen and provides async-compatible stdin/stdout streams using anyio's FileReadStream and FileWriteStream. This allows MCP STDIO clients to work on Windows without encountering the NotImplementedError. Based on PR #596 by @theailanguage Github-Issue: #596 Reported-by: theailanguage
The DummyProcess class wasn't closing file handles in its __aexit__ method, causing ResourceWarning errors in CI tests on Windows. This commit adds proper cleanup to close both the async stream wrappers and underlying raw file handles when the process context manager exits. This prevents file descriptor leaks and eliminates the ResourceWarning errors seen in pytest output on Windows CI.
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9 tasks
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Closing in favor of #596 |
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Warning
THIS IS FOR REVIEW ONLY - PR #596 should be the one that gets merged.
This is a rebase of PR #596 (#596) by @theailanguage with merge conflicts resolved and (presumed) unrelated changes removed.
Original fix by @theailanguage implements a fallback mechanism for Windows where asyncio.create_subprocess_exec raises NotImplementedError. Uses subprocess.Popen directly with async stream wrappers to maintain compatibility.
The DummyProcess class wraps the synchronous Popen object and provides the same interface as anyio.Process for seamless integration.
Resolves subprocess creation issues on Windows, particularly in environments with different event loop configurations like Streamlit.