This is a backport of PR #13249 as merged into master (3c6cf44).

What do these changes do?

The llhttp callbacks in the C parser are declared except -1, which promises Cython that a -1 return always has an exception pending. The callbacks actually return -1 as a plain abort status after catching the error and stashing it for later delivery. That is fine when llhttp calls them, but feed_data also calls cb_on_body directly to drain pending decompressed data; when the decompressor raises during that drain, Cython takes the error path with no exception set and crashes in __Pyx_AddTraceback on Python 3.12 and newer. This happens in the wild with brotlicffi 1.2, see python-hyper/brotlicffi#225 and cython/cython#7857.

The callbacks are now declared except? -1 so Cython checks PyErr_Occurred() before taking the error path, and the drain call handles the failure explicitly; the error reaches the user through the payload as ContentEncodingError like other payload errors.

Are there changes in behavior for the user?

A decompression failure while draining pending data now raises ContentEncodingError instead of crashing the interpreter.

Is it a substantial burden for the maintainers to support this?

No, the exception declarations now match what the callbacks actually do.

Related issue number

Fixes #13203.

Checklist

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• Unit tests for the changes exist
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tests/test_http_parser.py Fatal Python error: Segmentation fault

tests/test_http_parser.py::test_decompress_error_while_draining_pending_data[py-parser] PASSED
tests/test_http_parser.py::test_decompress_error_while_draining_pending_data[c-parser] PASSED
835 passed, 2 skipped, 6 deselected, 3 xfailed in 1.89s

AIOHTTP_NO_EXTENSIONS=1: 1 passed

if (unlikely(__pyx_t_5 == ((int)-1) && PyErr_Occurred())) __PYX_ERR(0, 637, __pyx_L1_error)

Drafted with Claude Code (Fable 5); reviewed by bdraco.