fix: Windows MCP encoding crash and build abort on empty/corrupted PDFs - #391
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ASuresh0524 merged 2 commits intoJul 31, 2026
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July 31, 2026 17:05
Two Windows fixes in the MCP stdio server:
- _run_leann now decodes subprocess output with encoding='utf-8'
(errors='replace'). text=True alone falls back to the locale
encoding (e.g. GBK on Chinese Windows), which crashed the
subprocess reader thread on any emoji/CJK output and made every
tool call return {"text": null}.
- _run_leann now actually uses the existing _leann_cmd() helper
(sys.executable -m leann) instead of a bare 'leann' lookup, so the
CLI is found even when the leann console-script is not on PATH
(common when leann_mcp is launched by MCP client wrappers).
A 0-byte or corrupted PDF made fitz.open()/pdfplumber.open() raise (pymupdf.EmptyFileError etc.) and aborted the entire 'leann build'. Return an empty string for unopenable/empty PDFs so the rest of the document set still gets indexed.
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What does this PR do?
Two Windows fixes, both reproduced on Windows 11 + Python 3.11 (leann-core 0.3.7):
errors="replace").Plain
text=Truedecodes subprocess output with the locale encoding (GBK onChinese Windows). Since the
leannCLI prints emoji/CJK (UTF-8), the subprocessreader thread crashed with
UnicodeDecodeErrorand every MCP tool call returned{"text": null}. Fixed by passingencoding="utf-8"explicitly._leann_cmd()helper._leann_cmd()(sys.executable -m leann) was defined but never called;_run_leannstill did a bare["leann", ...]lookup, which fails withWinError 2when theleannconsole-script is not on PATH — exactly thesituation the helper's docstring describes (MCP client wrappers on Windows).
leann build.A 0-byte or damaged PDF raised
pymupdf.EmptyFileError(or similar) fromfitz.open()/pdfplumber.open()and aborted the entire build. Bothextract_pdf_text_with_pymupdfandextract_pdf_text_with_pdfplumbernowreturn
""for empty/unopenable files so the rest of the document set stillgets indexed.
Note: the related Windows crash in
search_documentsJSON mode (ctypes.CDLL(None))was already fixed by #312.
Related Issues
Relates to #14
Checklist
uv run pytest) — ran related suites:test_mcp_standalone.py,test_mcp_integration.py,test_cli_verbosity.py,test_rebuild_cli.py(26 passed); empty-PDF extraction verified manually
ruff formatandruff check)pre-commit run --all-files) — not run (pre-commit not installed locally)