MIME-Version header parsing leaks ValueError for oversized numeric components

[augusto-rehfeldt]

Bug report

Bug description:

Documented behaviour: MIMEVersionHeader.value_parser documents the grammar as "mime-version = [CFWS] 1digit [CFWS] "." [CFWS] 1digit [CFWS]". BaseHeader's subclass contract states: "The parser should not, insofar as practical, raise any errors. Defects should be added to the list instead." Neither grammar repetition imposes a digit-count bound.

Expected: Construct the header without raising; record a defect if the version components cannot be represented under the active conversion limit.

Actual: Header construction raises ValueError when the major version contains 4301 digits and the integer-string conversion limit is 4300.

import re
import sys
import email.headerregistry as hr

limit = getattr(sys, "get_int_max_str_digits", lambda: 0)()
value = "1" * (limit + 1 if limit else 4301) + ".0"
expected = "constructed without exception" if re.fullmatch(r"[0-9]+\.[0-9]+", value) else None

if expected is None:
    print("REFUTATION REJECTED: input does not match the documented grammar")
else:
    try:
        hr.HeaderRegistry()("MIME-Version", value)
    except Exception as e:
        print(f"REFUTATION CONFIRMED: input={value!r}\nactual: {type(e).__name__}: {e}\nexpected: {expected}")
    else:
        print("REFUTATION REJECTED: constructed without exception")

Output on Python 3.14.6 (Windows-11-10.0.26220-SP0), standard library email.headerregistry:

111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111.0'
actual: ValueError: Exceeds the limit (4300 digits) for integer string conversion: value has 4301 digits; use sys.set_int_max_str_digits() to increase the limit
expected: constructed without exception

This report was found and written by an automated property-testing tool I run (bugforge). The reproducer above was executed and its output is pasted unedited; no person reviewed the report before it was filed. The search script is in https://github.com/augusto-rehfeldt/bugforge-results/tree/main/email.headerregistry-20261003-060502-c4

CPython versions tested on:

3.14

Operating systems tested on:

Windows

[ZeroIntensity]

See #158748 (comment).