This is a backport of PR #13246 as merged into master (25561d9).

What do these changes do?

llhttp strips the OWS before a header value but leaves the OWS after it, and _process_header() decodes the raw bytes as-is. So the C parser keeps trailing spaces and tabs where the Python parser strips them:

>>> feed(b"GET / HTTP/1.1\r\nHost: a\r\ntest: \t value \t \r\n\r\n").headers["test"]
'value'        # HttpRequestParserPy
'value \t '    # HttpRequestParserC

RFC 9110 section 5.5 says the OWS on both sides is excluded from the field value, and HeadersParser.parse_headers() already does bvalue.strip(b" \t") for both headers and raw_headers (there is a comment there saying raw does not mean the OWS is kept). This does the same in the C parser.

test_http_request_parser_utf8_request_line covers this for the Python parser, but it is xfailed for the C parser over an unrelated URL difference, so the gap was not visible.

Are there changes in behavior for the user?

Header values read through the C parser no longer carry trailing spaces or tabs, so both parsers now return the same thing. raw_headers changes the same way.

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

No, it is three lines in _process_header() and removes a difference between the two parsers.

Related issue number

None.

Checklist

• I think the code is well written
• Unit tests for the changes exist
• Documentation reflects the changes — N/A, no API change
• If you provide code modification, please add yourself to CONTRIBUTORS.txt
• Add a new news fragment into the CHANGES/ folder

$ PYTHONPATH='.' pytest tests/test_http_parser.py -k whitespace_around_header_value -v
tests/test_http_parser.py::test_whitespace_around_header_value[py-parser] PASSED
tests/test_http_parser.py::test_whitespace_around_header_value[c-parser] PASSED

E       AssertionError: assert 'value \t ' == 'value'
FAILED tests/test_http_parser.py::test_whitespace_around_header_value[c-parser]
1 failed, 1 passed

$ PYTHONPATH='.' pytest tests/test_http_parser.py
837 passed, 6 deselected, 3 xfailed

$ PYTHONPATH='.' pytest --numprocesses=auto
15 failed, 4932 passed, 23 skipped, 17 xfailed

Drafted with Claude Opus 5 (Claude Code); reviewed by @LuShadowX.