fix: default encoding_error_handler to 'replace' in StdioServerParameters - #2495
fix: default encoding_error_handler to 'replace' in StdioServerParameters#2495Christian-Sidak wants to merge 6 commits into
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…ters Match the server-side behavior from PR modelcontextprotocol#2302: replace invalid UTF-8 bytes with U+FFFD so malformed child output surfaces as a JSON parse error in the read stream instead of crashing the transport task group. Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
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Friendly bump -- let me know if anything needs changing. |
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Friendly bump -- let me know if anything needs changing. |
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Fixed the CI failures: the new test exercises the except Exception as exc path in stdio_client (invalid UTF-8 is now decoded via replace handler and then fails JSON parsing), which made the # pragma: no cover annotation stale. Removed it so strict-no-cover no longer flags those lines. |
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Remove time.sleep(1) so the child exits immediately after writing, then drop the early-break guard. The loop now terminates by exhaustion rather than break, which covers the previously-missing 532->537 branch and restores 100 % coverage.
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Fixed the coverage gap: branch 532->537 was the async-for exhaustion path, never reached because the loop always exited via break. Removed time.sleep(1) from the child script so the process exits immediately after writing the two lines, then dropped the early-break guard. The loop now terminates by exhaustion, covering both branches and restoring 100% coverage. |
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Fixed the ruff PERF401 lint error: replaced the async for + items.append pattern with items.extend([item async for item in read_stream]). The Windows/Python 3.14 coverage failure (lines 290-296, 850-851 of server.py) appears to be a pre-existing platform-specific gap unrelated to this PR — all 1172 tests pass on that platform and the uncovered lines are in server.py, which this PR does not touch. |
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Closing as a duplicate of #2456, which was opened first with the same change plus broader teardown handling. Appreciated the iteration on CI here — thanks for the contribution. |
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Summary
stdio_client crashed with an ExceptionGroup when the child process wrote invalid UTF-8 bytes to stdout because StdioServerParameters.encoding_error_handler defaulted to "strict".
This was already fixed on the server side in PR #2302; this PR applies the same one-line fix to the client side.
Change: default encoding_error_handler from "strict" to "replace" so malformed bytes are replaced with U+FFFD, which then fails JSON parsing and is delivered as an in-stream Exception — keeping the transport alive for subsequent valid messages.
Test
Added test_stdio_client_invalid_utf8 to tests/client/test_stdio.py: spawns a child that writes b"\xff\xfe\n" followed by a valid JSON-RPC line, and asserts the first stream item is an Exception and the second is a SessionMessage.
Fixes #2454