Silently discard epilogue data after the closing boundary#259
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Django's MultiPartParser and Werkzeug's sansio multipart parser both silently accept (and ignore) the optional CRLF + epilogue that RFC 2046 section 5.1.1 allows after the closing boundary. python-multipart was logging "Skipping data after last boundary" instead, and the single- chunk guard added in #193 also missed the case where the trailing CRLF was split across two writes - a trailing `\r` at the end of one chunk would fall through to the warning branch because `i + 1 < length` was false, even though the `\n` arrived in the next chunk. Drop the warning and the split-chunk guard entirely. The epilogue is short-circuited the same way as before (no O(N) scan), just without the spurious log line. Closes #246.
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I ran a quick parser-only benchmark comparing this PR ( Payload shape: valid = (
b"--boundary\r\n"
b"Content-Disposition: form-data; name=\"f\"\r\n"
b"\r\nval\r\n"
b"--boundary--"
)
crlf_epilogue = valid + b"\r\n" * (size // 2)
non_crlf_epilogue = valid + b"X" * sizeResults:
So this makes CRLF epilogue handling take the same short-circuit path as other epilogue data. |
Kludex
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Apr 10, 2026
Kludex
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Apr 10, 2026
tests/test_multipart.py
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| Covers both the single-chunk case and the case where the trailing | ||
| CRLF is split across `write()` calls (e.g. when `\r` and `\n` land in | ||
| separate TCP chunks behind a proxy). |
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Can we use the 120 line limit?
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Summary
"Skipping data after last boundary"warning. RFC 2046 section 5.1.1 allows an optional CRLF + epilogue after the closing boundary, and both Django'sMultiPartParserand Werkzeug's sansio multipart parser accept it silently - python-multipart was the outlier."Skipping data after last boundary"warning when CRLF is split across chunks #246: the previous guard atmultipart.py:1417only paired\rwith\nwhen both landed in the samewrite()call, so a trailing\rat the end of one chunk followed by\nin the next (common behind network proxies) produced a spurious warning.i = length; break, preserving the O(1) behavior added in Hard break if found data after last boundary onMultipartParser#189 - no epilogue scanning, no DoS surface.Test plan
test_multipart_parser_epilogue_emits_no_warningscovers single-chunk CRLF, split CRLF across two writes, boundary-then-CRLF split, and non-empty epilogue - all asserting zero warnings.test_multipart_parser_data_after_last_boundary, 50M trailing bytes) still short-circuit.pytest --cov- 134 passed, 100% coverage.ruff check,ruff format --check,mypy --strictall clean.Closes #246.