Replace per-byte partial-boundary scan with rfind lookbehind - #300
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When `find` cannot locate a whole boundary in part data, the tail may hold a partial boundary that completes in the next chunk. The old fallback seeded the per-byte matcher at the tail, which thrashed on CR/LF-dense bodies: `\r\n` matches the boundary prefix, fails at `-`, resets, reconsiders, and re-runs `find` for every `\r\n` pair near the chunk end. Since `self.boundary` is `\r\n--` + boundary and an RFC boundary cannot contain CR, the last CR in the tail is the only candidate prefix start. Anchor on it with `rfind`, confirm with `startswith`, carry the partial via `index`, and let the existing end-of-chunk flush emit the data and re-mark the lookbehind. This mirrors multer's lookbehind strategy. worstcase_crlf goes from ~2700 to ~18500 MB/s (6.9x), reaching parity with the LF case; LF, boundary-char, and file-upload paths are unchanged. Verified behaviorally identical to the previous parser across 82k differential comparisons (every chunk-split strategy incl. byte-by-byte, with the boundary edge landing on every offset).
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This MR contains the following updates: | Package | Type | Update | Change | OpenSSF | |---|---|---|---|---| | [debugpy](https://aka.ms/debugpy) ([source](https://github.com/microsoft/debugpy)) | dev | patch | `1.8.20` → `1.8.21` | [](https://securityscorecards.dev/viewer/?uri=github.com/microsoft/debugpy) | | [numpy](https://github.com/numpy/numpy) ([changelog](https://numpy.org/doc/stable/release)) | dependencies | patch | `2.4.4` → `2.4.6` | [](https://securityscorecards.dev/viewer/?uri=github.com/numpy/numpy) | | [pydantic-settings](https://github.com/pydantic/pydantic-settings) ([changelog](https://github.com/pydantic/pydantic-settings/releases)) | dependencies | patch | `2.14.0` → `2.14.2` | [](https://securityscorecards.dev/viewer/?uri=github.com/pydantic/pydantic-settings) | | [python-multipart](https://github.com/Kludex/python-multipart) ([changelog](https://github.com/Kludex/python-multipart/blob/master/CHANGELOG.md)) | dependencies | patch | `^0.0.22` → `^0.0.32` | [](https://securityscorecards.dev/viewer/?uri=github.com/Kludex/python-multipart) | | [types-requests](https://github.com/python/typeshed) ([changelog](https://github.com/typeshed-internal/stub_uploader/blob/main/data/changelogs/requests.md)) | dependencies | patch | `2.32.0.20240523` → `2.32.4.20260324` | [](https://securityscorecards.dev/viewer/?uri=github.com/python/typeshed) | --- ### Release Notes <details> <summary>microsoft/debugpy (debugpy)</summary> ### [`v1.8.21`](https://github.com/microsoft/debugpy/releases/tag/v1.8.21): debugpy v1.8.21 [Compare Source](microsoft/debugpy@v1.8.20...v1.8.21) Fixes for: - Return evaluate result in DAP response body instead of writing to stdout: [#​2027](microsoft/debugpy#2027) - Prevent invalid `scopes` request from crashing debug session: [#​2026](microsoft/debugpy#2026) - Skip uninitialized `__slots__` in variable resolver: [#​2024](microsoft/debugpy#2024) - Handle `-c` arguments that are `bytes` instead of `str`: [#​2021](microsoft/debugpy#2021) - Fix evaluation of variables from chained exception frames: [#​2018](microsoft/debugpy#2018) - `ContinueRequest` with a specific `threadId` no longer resumes all threads (in-process adapter): [#​2012](microsoft/debugpy#2012) - Avoid strong reference to exceptions during unwind: [#​2008](microsoft/debugpy#2008) - Show error message on evaluate failures in the hover context: [#​2006](microsoft/debugpy#2006) - Display `dlerror` output when `dlopen` fails: [#​2000](microsoft/debugpy#2000) - Replace removed `pkgutil.get_loader` with `importlib.util.find_spec` in `get_fullname`: [#​1998](microsoft/debugpy#1998) Enhancements: - Add option to ignore all system exit codes: [#​2017](microsoft/debugpy#2017) - Pull changes from pydevd up to March 2026: [#​2010](microsoft/debugpy#2010) Infrastructure work: - Suppress Flawfinder false positives on Cython memcpy / read-loop iterators (TSA [#​2816216](https://github.com/microsoft/debugpy/issues/2816216), [#​2816217](https://github.com/microsoft/debugpy/issues/2816217), [#​2816218](https://github.com/microsoft/debugpy/issues/2816218), [#​2816219](https://github.com/microsoft/debugpy/issues/2816219), [#​2816220](https://github.com/microsoft/debugpy/issues/2816220)): [#​2028](microsoft/debugpy#2028), [#​2029](microsoft/debugpy#2029), [#​2030](microsoft/debugpy#2030), [#​2031](microsoft/debugpy#2031), [#​2032](microsoft/debugpy#2032) Thanks to [@​maxbachmann](https://github.com/maxbachmann), [@​mfussenegger](https://github.com/mfussenegger), and [@​sambrightman](https://github.com/sambrightman) for the commits. </details> <details> <summary>numpy/numpy (numpy)</summary> ### [`v2.4.6`](https://github.com/numpy/numpy/releases/tag/v2.4.6): (May 18, 2026) [Compare Source](numpy/numpy@v2.4.5...v2.4.6) ### NumPy 2.4.6 Release Notes NumPy 2.4.6 is a quick release that fixes a regression discovered in the 2.4.5 release. This release supports Python versions 3.11-3.14 #### Contributors A total of 4 people contributed to this release. People with a "+" by their names contributed a patch for the first time. - !EarlMilktea - Charles Harris - Sebastian Berg - Warren Weckesser #### Pull requests merged A total of 4 pull requests were merged for this release. - [#​31444](numpy/numpy#31444): MAINT: Prepare 2.4.x for further development - [#​31453](numpy/numpy#31453): BUG: Fix regression in `arr.conj()` - [#​31459](numpy/numpy#31459): BUG: `np.linalg.svd(..., hermitian=True)` returns non-unitary... - [#​31460](numpy/numpy#31460): BUG: Don't call INCREF/DECREF on descr in NpyStringAcquireAllocator... ### [`v2.4.5`](https://github.com/numpy/numpy/releases/tag/v2.4.5): (May 15, 2026) [Compare Source](numpy/numpy@v2.4.4...v2.4.5) ### NumPy 2.4.5 Release Notes NumPy 2.4.5 is a patch release that fixes bugs discovered after the 2.4.4 release, has some typing improvements, and maintains infrastructure. This release supports Python versions 3.11-3.14 #### Contributors A total of 17 people contributed to this release. People with a "+" by their names contributed a patch for the first time. - Aleksei Nikiforov - Anarion Zuo + - Ankit Ahlawat - Breno Favaretto + - Charles Harris - Igor Krivenko + - Ijtihed Kilani + - Joren Hammudoglu - Maarten Baert + - Matti Picus - Nathan Goldbaum - Praneeth Kodumagulla + - Ralf Gommers - RoomWithOutRoof + - Sebastian Berg - Warren Weckesser - div + #### Pull requests merged A total of 28 pull requests were merged for this release. - [#​31093](numpy/numpy#31093): MAINT: Prepare 2.4.x for further development - [#​31182](numpy/numpy#31182): TYP: fix `np.shape` assignability issue for python lists ([#​31171](numpy/numpy#31171)) - [#​31197](numpy/numpy#31197): ENH: Return rank 0 for empty matrices in matrix\_rank ([#​30422](numpy/numpy#30422)) - [#​31198](numpy/numpy#31198): CI/BUG: add native jobs for s390x, fix bug in `pack_inner`... - [#​31199](numpy/numpy#31199): BUG: f2py map complex\_long\_double to NPY\_CLONGDOUBLE - [#​31205](numpy/numpy#31205): MAINT: f2py: Stop setting re.\_MAXCACHE to 50. - [#​31206](numpy/numpy#31206): BUG: fix heap buffer overflow in timedelta to string casts - [#​31207](numpy/numpy#31207): MAINT: Rename ppc64le and s390x workflow ([#​31121](numpy/numpy#31121)) - [#​31208](numpy/numpy#31208): BUG: Fix matvec/vecmat in-place aliasing (out=input produces... - [#​31209](numpy/numpy#31209): TYP: `tile`: accept numpy scalars and arrays as second argument... - [#​31211](numpy/numpy#31211): DEP: Undo deprecation for np.dtype() signature used by old pickles... - [#​31212](numpy/numpy#31212): REV: Manual revert of float16 svml use ([#​31178](numpy/numpy#31178)) - [#​31222](numpy/numpy#31222): TYP: `ix_` fix for boolean and non-1d input ([#​31218](numpy/numpy#31218)) - [#​31329](numpy/numpy#31329): BUG: incorrect temp elision for new-style (NEP 43) user-defined... - [#​31330](numpy/numpy#31330): TYP: fix sliding\_window\_view axis parameter typing - [#​31335](numpy/numpy#31335): BUG: Prevent deadlock due to downstream importing NumPy in dlopen... - [#​31336](numpy/numpy#31336): BUG: Fix segfault in nditer.multi\_index when \_\_getitem\_\_ raises... - [#​31338](numpy/numpy#31338): TYP: Fix ruff lint error - [#​31357](numpy/numpy#31357): BUG: fix memory leak in np.zeros when fill-zero loop raises ([#​31320](numpy/numpy#31320)) - [#​31358](numpy/numpy#31358): BUG: np.einsum() fails with a 0-dimensional out argument and... - [#​31379](numpy/numpy#31379): BUG: Fix signed overflow issue in npy\_gcd for INT\_MIN on s390x... - [#​31383](numpy/numpy#31383): CI: remove Cirrus CI FreeBSD job ([#​31380](numpy/numpy#31380)) - [#​31390](numpy/numpy#31390): BUILD: newer MKL uses so.3 - [#​31391](numpy/numpy#31391): BLD/MAINT: improve support for Intel LLVM compilers - [#​31401](numpy/numpy#31401): BUG: Avoid UB in [safe]()\[add,sub,mul] helpers ([#​31396](numpy/numpy#31396)) - [#​31402](numpy/numpy#31402): BUG: exclude \_\_pycache\_\_ directories from wheels ([#​31397](numpy/numpy#31397)) - [#​31404](numpy/numpy#31404): TYP: `_NestedSequence` type parameter default to work around... - [#​31426](numpy/numpy#31426): TYP: Fix `DTypeLike` runtime type-checker support ([#​31425](numpy/numpy#31425)) </details> <details> <summary>pydantic/pydantic-settings (pydantic-settings)</summary> ### [`v2.14.2`](https://github.com/pydantic/pydantic-settings/releases/tag/v2.14.2) [Compare Source](pydantic/pydantic-settings@v2.14.1...v2.14.2) #### What's Changed This is a security patch release. - Prevent `NestedSecretsSettingsSource` from following symlinks outside `secrets_dir` by [@​hramezani](https://github.com/hramezani) in [#​889](pydantic/pydantic-settings#889) - Prepare release 2.14.2 by [@​hramezani](https://github.com/hramezani) in [#​890](pydantic/pydantic-settings#890) ##### Security Fixes [GHSA-4xgf-cpjx-pc3j](GHSA-4xgf-cpjx-pc3j): `NestedSecretsSettingsSource` with `secrets_nested_subdir=True` could follow a symbolic link inside `secrets_dir` pointing outside it, reading out-of-tree files into settings values and bypassing the `secrets_dir_max_size` cap. Affected versions: `>= 2.12.0, < 2.14.2`. **Full Changelog**: <pydantic/pydantic-settings@v2.14.1...v2.14.2> ### [`v2.14.1`](https://github.com/pydantic/pydantic-settings/releases/tag/v2.14.1) [Compare Source](pydantic/pydantic-settings@v2.14.0...v2.14.1) #### What's Changed - Bump the python-packages group with 4 updates by [@​dependabot](https://github.com/dependabot)\[bot] in [#​850](pydantic/pydantic-settings#850) - Bump the python-packages group with 5 updates by [@​dependabot](https://github.com/dependabot)\[bot] in [#​854](pydantic/pydantic-settings#854) - Bump the github-actions group with 3 updates by [@​dependabot](https://github.com/dependabot)\[bot] in [#​853](pydantic/pydantic-settings#853) - Bump the python-packages group with 2 updates by [@​dependabot](https://github.com/dependabot)\[bot] in [#​856](pydantic/pydantic-settings#856) - Fix field named `cls` conflicting with classmethod parameter by [@​hramezani](https://github.com/hramezani) in [#​858](pydantic/pydantic-settings#858) - Prepare release 2.14.1 by [@​hramezani](https://github.com/hramezani) in [#​859](pydantic/pydantic-settings#859) **Full Changelog**: <pydantic/pydantic-settings@v2.14.0...v2.14.1> </details> <details> <summary>Kludex/python-multipart (python-multipart)</summary> ### [`v0.0.32`](https://github.com/Kludex/python-multipart/blob/HEAD/CHANGELOG.md#0032-2026-06-04) [Compare Source](Kludex/python-multipart@0.0.31...0.0.32) - Speed up partial-boundary scanning for CR/LF-dense part data [#​300](Kludex/python-multipart#300). ### [`v0.0.31`](https://github.com/Kludex/python-multipart/blob/HEAD/CHANGELOG.md#0031-2026-06-04) [Compare Source](Kludex/python-multipart@0.0.30...0.0.31) - Speed up multipart header parsing and callback dispatch [#​295](Kludex/python-multipart#295). - Bound header field name size before validating [#​296](Kludex/python-multipart#296). - Validate `Content-Length` is non-negative in `parse_form` [#​297](Kludex/python-multipart#297). ### [`v0.0.30`](https://github.com/Kludex/python-multipart/blob/HEAD/CHANGELOG.md#0030-2026-05-31) [Compare Source](Kludex/python-multipart@0.0.29...0.0.30) - Parse `application/x-www-form-urlencoded` bodies per the WHATWG URL standard, treating only `&` as a field separator [#​290](Kludex/python-multipart#290). - Ignore RFC 2231/5987 extended parameters (`name*`, `filename*`) in `parse_options_header`, keeping the plain parameter authoritative per [RFC 7578 §4.2](https://datatracker.ietf.org/doc/html/rfc7578#section-4.2) [#​291](Kludex/python-multipart#291). ### [`v0.0.29`](https://github.com/Kludex/python-multipart/blob/HEAD/CHANGELOG.md#0029-2026-05-17) [Compare Source](Kludex/python-multipart@0.0.28...0.0.29) - Handle malformed RFC 2231 continuations in `parse_options_header` [#​270](Kludex/python-multipart#270). ### [`v0.0.28`](https://github.com/Kludex/python-multipart/blob/HEAD/CHANGELOG.md#0028-2026-05-10) [Compare Source](Kludex/python-multipart@0.0.27...0.0.28) - Speed up partial-boundary tail scan via `bytes.find` [#​281](Kludex/python-multipart#281). - Cap multipart boundary length at 256 bytes [#​282](Kludex/python-multipart#282). ### [`v0.0.27`](https://github.com/Kludex/python-multipart/blob/HEAD/CHANGELOG.md#0027-2026-04-27) [Compare Source](Kludex/python-multipart@0.0.26...0.0.27) - Add multipart header limits [#​267](Kludex/python-multipart#267). - Pass parse offsets via constructors [#​268](Kludex/python-multipart#268). ### [`v0.0.26`](https://github.com/Kludex/python-multipart/blob/HEAD/CHANGELOG.md#0026-2026-04-10) [Compare Source](Kludex/python-multipart@0.0.25...0.0.26) - Skip preamble before the first multipart boundary more efficiently [#​262](Kludex/python-multipart#262). - Silently discard epilogue data after the closing multipart boundary [#​259](Kludex/python-multipart#259). ### [`v0.0.25`](https://github.com/Kludex/python-multipart/blob/HEAD/CHANGELOG.md#0025-2026-04-10) [Compare Source](Kludex/python-multipart@0.0.24...0.0.25) - Add MIME content type info to `File` [#​143](Kludex/python-multipart#143). - Handle CTE values case-insensitively [#​258](Kludex/python-multipart#258). - Remove custom `FormParser` classes [#​257](Kludex/python-multipart#257). - Add `UPLOAD_DELETE_TMP` to `FormParser` config [#​254](Kludex/python-multipart#254). - Emit `field_end` for trailing bare field names on finalize [#​230](Kludex/python-multipart#230). - Handle multipart headers case-insensitively [#​252](Kludex/python-multipart#252). - Apply Apache-2.0 properly [#​247](Kludex/python-multipart#247). ### [`v0.0.24`](https://github.com/Kludex/python-multipart/blob/HEAD/CHANGELOG.md#0024-2026-04-05) [Compare Source](Kludex/python-multipart@0.0.23...0.0.24) - Validate `chunk_size` in `parse_form()` [#​244](Kludex/python-multipart#244). ### [`v0.0.23`](https://github.com/Kludex/python-multipart/blob/HEAD/CHANGELOG.md#0023-2026-04-05) [Compare Source](Kludex/python-multipart@0.0.22...0.0.23) - Remove unused `trust_x_headers` parameter and `X-File-Name` fallback [#​196](Kludex/python-multipart#196). - Return processed length from `QuerystringParser._internal_write` [#​229](Kludex/python-multipart#229). - Cleanup metadata dunders from `__init__.py` [#​227](Kludex/python-multipart#227). </details> --- - [ ] <!-- rebase-check -->If you want to rebase/retry this MR, check this box --- This MR has been generated by [Mend Renovate](https://github.com/renovatebot/renovate). <!--renovate-debug:eyJjcmVhdGVkSW5WZXIiOiI0My4xMTAuMTYiLCJ1cGRhdGVkSW5WZXIiOiI0My4yNDYuMSIsInRhcmdldEJyYW5jaCI6Im1haW4iLCJsYWJlbHMiOlsiZGVwZW5kZW5jaWVzIiwicmVub3ZhdGUiXX0=--> See merge request swiss-armed-forces/cyber-command/cea/loom!460 Co-authored-by: Loom MR Pipeline Trigger <group_103951964_bot_9504bb8dead6d4e406ad817a607f24be@noreply.gitlab.com> Co-authored-by: shrewd-laidback palace <shrewd-laidback-palace-736-c41-2c1-e464fc974@swiss-armed-forces-open-source.ch>
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What
When
findcannot locate a whole boundary in part data, the tail may hold a partial boundary that completes in the next chunk. The old fallback seeded the per-byte matcher at the tail, which thrashed on CR/LF-dense bodies:\r\nmatches the boundary prefix, fails at-, resets, reconsiders, and re-runsfindfor every\r\npair near the chunk end.Since
self.boundaryis\r\n--+ boundary and an RFC boundary cannot contain CR, the last CR in the tail is the only candidate prefix start. We anchor on it withrfind, confirm withstartswith, carry the partial viaindex, and let the existing end-of-chunk flush emit the data and re-mark the lookbehind. This mirrors multer's lookbehind strategy.Impact
Benchmarked against
multipart_bench(1MB part body, 64KB chunks, sansio variant):worstcase_crlfwas the slowest scenario across all pure-Python parsers; it is now the fastest, reaching parity with the LF case.Correctness
Verified behaviorally identical to the previous parser across 82k differential comparisons of the full callback-event stream and error type/offset: every chunk-split strategy (whole, byte-by-byte, fixed-size, random) plus an exhaustive two-chunk sweep with the boundary edge landing on every byte offset. Zero mismatches.
Adds a CRLF-dense corpus case (
crlf_dense_part_data) to the data-driven test suite, run both whole-write and byte-by-byte. 100% coverage maintained.AI Disclaimer
This PR was developed with the assistance of either Claude or Codex. I've reviewed and verified the changes.