[PR #11178/915338c7 backport][3.13] Fix cookie header parser ignoring reserved names

[patchback]

This is a backport of PR #11178 as merged into master (915338c).

What do these changes do?

This PR fixes the Cookie header parser to correctly handle reserved attribute names (like path, domain, secure) as regular cookies, per RFC 6265 Section 5.4.

Previously, Cookie headers like session=abc123; path=/api; secure=true would only parse session=abc123, incorrectly ignoring path and secure. Now all three are correctly parsed as cookies.

The fix:

• Adds a new parse_cookie_header() function specifically for RFC 6265 compliant Cookie header parsing
• Renames the existing parse_cookie_headers() to parse_set_cookie_headers() for clarity
• Updates all Cookie header parsing locations to use the new parser

Are there changes in behavior for the user?

Yes, Cookie headers containing reserved attribute names will now be parsed differently:

Before:

# Cookie: "session=abc123; path=/api; secure=true"
request.cookies == {"session": "abc123"}  # path and secure ignored

After:

# Cookie: "session=abc123; path=/api; secure=true"
request.cookies == {"session": "abc123", "path": "/api", "secure": "true"}

This is the correct behavior per RFC 6265 and matches what web browsers do.

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

No. This change:

• Simplifies the cookie parsing logic by having separate parsers for different header types
• Makes the code more RFC compliant and easier to understand
• Uses the same robust regex-based parsing approach as the existing parser
• Has comprehensive test coverage

Related issue number

This has likely been an issue since the beginning, as we previously used Python's SimpleCookie which has the same incorrect behavior. Now that we have our own parser (from PR #11112), we can fix this RFC compliance issue.

Checklist

• I think the code is well written
• Unit tests for the changes exist
• Documentation reflects the changes
• If you provide code modification, please add yourself to CONTRIBUTORS.txt
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  • Please keep alphabetical order, the file is sorted by names.
• Add a new news fragment into the CHANGES/ folder

  • name it <issue_or_pr_num>.<type>.rst (e.g. 588.bugfix.rst)

  • if you don't have an issue number, change it to the pull request
    number after creating the PR

    • .bugfix: A bug fix for something the maintainers deemed an
      improper undesired behavior that got corrected to match
      pre-agreed expectations.
    • .feature: A new behavior, public APIs. That sort of stuff.
    • .deprecation: A declaration of future API removals and breaking
      changes in behavior.
    • .breaking: When something public is removed in a breaking way.
      Could be deprecated in an earlier release.
    • .doc: Notable updates to the documentation structure or build
      process.
    • .packaging: Notes for downstreams about unobvious side effects
      and tooling. Changes in the test invocation considerations and
      runtime assumptions.
    • .contrib: Stuff that affects the contributor experience. e.g.
      Running tests, building the docs, setting up the development
      environment.
    • .misc: Changes that are hard to assign to any of the above
      categories.

  • Make sure to use full sentences with correct case and punctuation,
    for example:

    Fixed issue with non-ascii contents in doctest text files
    -- by :user:`contributor-gh-handle`.

    Use the past tense or the present tense a non-imperative mood,
    referring to what's changed compared to the last released version
    of this project.

[codspeed-hq]

CodSpeed Performance Report

Merging #11182 will not alter performance

_{Comparing patchback/backports/3.13/915338c7b02d843114e05a94508e6d91921e88d7/pr-11178 (ed18de8) with 3.13 (058dced)}

Summary

✅ 59 untouched benchmarks

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 98.31%. Comparing base (058dced) to head (ed18de8).
⚠️ Report is 173 commits behind head on 3.13.
✅ All tests successful. No failed tests found.

Additional details and impacted files

@@           Coverage Diff            @@
##             3.13   #11182    +/-   ##
========================================
  Coverage   98.30%   98.31%            
========================================
  Files         132      132            
  Lines       43289    43499   +210     
  Branches     2375     2379     +4     
========================================
+ Hits        42555    42765   +210     
  Misses        558      558            
  Partials      176      176            

Flag	Coverage Δ
CI-GHA	98.20% <100.00%> (+<0.01%)	⬆️
OS-Linux	97.95% <100.00%> (+<0.01%)	⬆️
OS-Windows	95.66% <100.00%> (+0.02%)	⬆️
OS-macOS	97.20% <100.00%> (+<0.01%)	⬆️
Py-3.10.11	96.84% <100.00%> (+<0.01%)	⬆️
Py-3.10.17	97.34% <100.00%> (+0.17%)	⬆️
Py-3.10.18	?
Py-3.11.12	97.53% <100.00%> (+0.19%)	⬆️
Py-3.11.13	?
Py-3.11.9	97.04% <100.00%> (+0.01%)	⬆️
Py-3.12.10	97.87% <100.00%> (+0.01%)	⬆️
Py-3.13.3	97.84% <100.00%> (-0.02%)	⬇️
Py-3.13.4	96.88% <100.00%> (?)
Py-3.9.13	96.74% <100.00%> (+0.01%)	⬆️
Py-3.9.22	97.23% <100.00%> (+0.58%)	⬆️
Py-3.9.23	?
Py-pypy7.3.16	90.85% <100.00%> (-3.36%)	⬇️
VM-macos	97.20% <100.00%> (+<0.01%)	⬆️
VM-ubuntu	97.95% <100.00%> (+<0.01%)	⬆️
VM-windows	95.66% <100.00%> (+0.02%)	⬆️

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