Title: fix(stdio_client): tolerate invalid UTF-8 from child stdout by shaun0927 · Pull Request #2456 · modelcontextprotocol/python-sdk · GitHub
Open Graph Title: fix(stdio_client): tolerate invalid UTF-8 from child stdout by shaun0927 · Pull Request #2456 · modelcontextprotocol/python-sdk
X Title: fix(stdio_client): tolerate invalid UTF-8 from child stdout by shaun0927 · Pull Request #2456 · modelcontextprotocol/python-sdk
Description: Fixes #2454 Summary stdio_client() currently decodes child stdout with encoding_error_handler="strict", so a malformed UTF-8 line can raise during TextReceiveStream(...) iteration and crash the transport task group. This PR makes the client follow the same strategy that stdio_server() already uses after #2302: decode with errors="replace" let malformed lines fail JSON validation surface those failures as in-stream exceptions instead of killing the transport It also treats abrupt child shutdowns (BrokenResourceError / ConnectionResetError) as normal shutdown-time conditions in the background stdio tasks. Motivation and Context PR #2302 fixed the server side so invalid UTF-8 on stdin becomes a parse error instead of a transport crash. The client side still behaved asymmetrically: a buggy or non-compliant child process could kill the Python client with a single malformed stdout line even if the next line was valid JSON-RPC. That makes the client less robust than the server for the same class of malformed stdio input. How Has This Been Tested? Added a focused regression test in tests/client/test_stdio.py that spawns a child process which writes: one malformed UTF-8 line (b"\xff\xfe\n") one valid JSON-RPC line Without this patch, the transport fails before the valid line is delivered. With this patch: the first item from the read stream is an Exception the second item is the valid SessionMessage Local verification: uv run --frozen pytest tests/client/test_stdio.py uv run --frozen ruff check src/mcp/client/stdio.py tests/client/test_stdio.py uv run --frozen pyright src/mcp/client/stdio.py Breaking Changes None. Types of changes Bug fix (non-breaking change which fixes an issue) New feature (non-breaking change which adds functionality) Breaking change (fix or feature that would cause existing functionality to change) Documentation update Checklist I have read the MCP Documentation My code follows the repository's style guidelines New and existing tests pass locally I have added appropriate error handling I have added or updated documentation as needed
Open Graph Description: Fixes #2454 Summary stdio_client() currently decodes child stdout with encoding_error_handler="strict", so a malformed UTF-8 line can raise during TextReceiveStream(...) iteration and cra...
X Description: Fixes #2454 Summary stdio_client() currently decodes child stdout with encoding_error_handler="strict", so a malformed UTF-8 line can raise during TextReceiveStream(...) iteration...
Opengraph URL: https://github.com/modelcontextprotocol/python-sdk/pull/2456
X: @github
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