Raise BadTTL for non-decimal Unicode digits in dns.ttl.from_text()

[Sanjays2402]

What

dns.ttl.from_text() raises a bare ValueError instead of the documented dns.ttl.BadTTL when the text contains a non-decimal Unicode "digit". This also leaks out of the public zone-file parser as a raw ValueError rather than a clean dns.exception.SyntaxError.

Root cause

from_text() gates its integer parsing on str.isdigit() and then calls int():

if text.isdigit():
    total = int(text)
...
    for c in text:
        if c.isdigit():
            current *= 10
            current += int(c)

str.isdigit() returns True for Unicode characters in category No (e.g. the superscript ² U+00B2, or the Ethiopic digit ፩ U+1369), but int() only accepts decimal digits. So such input passes the isdigit() gate and then blows up inside int() with a bare ValueError, escaping the parser's own validation.

The function's docstring explicitly promises :raises dns.ttl.BadTTL:, so this is a contract violation.

Before (on main)

>>> import dns.ttl, dns.zone
>>> dns.ttl.from_text("\u00b2")
ValueError: invalid literal for int() with base 10: '²'
>>> dns.zone.from_text("@ 3\u00b2 IN A 1.2.3.4\n", origin="example.")
ValueError: invalid literal for int() with base 10: '3²'
>>> dns.zone.from_text("$TTL 1\u00b2\n@ IN A 1.2.3.4\n", origin="example.")
ValueError: invalid literal for int() with base 10: '1²'

After

>>> dns.ttl.from_text("\u00b2")
dns.ttl.BadTTL
>>> dns.zone.from_text("@ 3\u00b2 IN A 1.2.3.4\n", origin="example.")
dns.exception.SyntaxError: ...

Fix

Switch both isdigit() checks to isdecimal().

This is exactly behaviour-preserving for every valid TTL. For a single character, int()-acceptance is identical to str.isdecimal(), and isdecimal() is a strict subset of isdigit():

# int()-acceptance != isdecimal(): 0 chars over the whole Unicode range
# isdecimal-but-not-isdigit chars: 0

So no previously valid TTL is rejected; only the non-decimal "digits" that already crashed are now cleanly reported as BadTTL.

Tests

Added test_non_decimal_unicode_digits, covering both the all-digit fast path and the BIND-style units path ("\u00b2", "1\u00b2", "\u00b2w", "1\u00b2s", "\u1369").

Proven to guard the bug (stash only the source fix, keep the test):

# without the fix:
FAILED tests/test_ttl.py::TTLTestCase::test_non_decimal_unicode_digits
  ValueError: invalid literal for int() with base 10: '²'  (dns/ttl.py:46)
# with the fix:
1 passed

Verification

• tests/test_ttl.py: 10 passed
• tests/test_zone.py tests/test_tokenizer.py: 169 passed
• Full suite: 1281 passed, 118 skipped (the single test_basic_getaddrinfo failure is a pre-existing environment artifact — the local system resolver returns IPv4-mapped IPv6 for dns.google — present on main before this change, unrelated to it).
• ruff check, ruff format --check, black --check clean on the changed files.

Diff is +17 / −2 across dns/ttl.py, tests/test_ttl.py, and a doc/whatsnew.rst bullet.

[rthalley]

Thanks! I will look at all the other isdigit() calls as they probably should be isdecimal() too.