This is a backport of PR #13581 as merged into master (9c77642).

What do these changes do?

BaseRequest.http_range now matches the range unit name case-insensitively (re.IGNORECASE), per RFC 9110 §14.1.1 ("All range unit names are case-insensitive").

Previously a valid header like Range: Bytes=0-499 failed the ^bytes=(\d*)-(\d*)$ regex, raising ValueError("range not in acceptable format"), which FileResponse converts into 416 Requested Range Not Satisfiable — even for a perfectly satisfiable range. Only lowercase bytes= worked.

Are there changes in behavior for the user?

Yes, for the better: case variants of the range unit (Bytes, BYTES, bYtEs, …) are now accepted and yield 206 Partial Content where lowercase already did. Behavior for lowercase bytes= and for genuinely malformed ranges (non-bytes units, non-numeric bounds, multi-range, empty) is unchanged — those still raise the same ValueError.

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

No. One regex flag; no API surface change; the pure-Python http_range property is the only code path touched. FileResponse consumes it, so the fix propagates automatically.

Related issue number

Fixes #13580

Checklist

• I think the code is well written
• Unit tests for the changes exist
• Documentation reflects the changes (N/A — bug fix, no user-facing docs to update; CHANGES fragment added)
• If you provide code modification, please add yourself to CONTRIBUTORS.txt
  • The format is .
  • 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.

$ python -m pytest -o addopts="" -p no:aiohttp tests/test_web_request.py -q
143 passed in 0.68s

Range: bytes=0-3   -> HTTP/1.1 206 Partial Content      (control)
Range: Bytes=0-3   -> HTTP/1.1 206 Partial Content      (fixed; was 416)
Range: BYTES=0-3   -> HTTP/1.1 206 Partial Content      (fixed; was 416)

Drafted with Hermes Agent (deepseek-v4-flash); reviewed by Manny7717.