* fix(robots-check): stop a leading BOM or an undecodable rule from reading as allowed
Two decoding edge cases left the robots gate failing open. Both were
flagged as follow-ups in #506.
A robots.txt saved with a UTF-8 byte-order mark decodes to a body that
starts with U+FEFF, so its first field read as U+FEFF + "user-agent". A
leading "User-agent: *" went unseen, every rule in that group was
dropped for want of an agent, and "Disallow: /" read as allow-all.
_groups() and is_robots_body() now skip one leading U+FEFF, as Google's
reference parser does, which covers every caller of allowed(). This
predates #506: the old code-page decode hid the line the same way.
Since #506 pinned curl's output to UTF-8 with errors='replace', a
non-conformant robots.txt saved in a legacy code page (cp1254,
ISO-8859-9) with raw non-ASCII bytes in a rule decodes them to U+FFFD.
That rule can never match and was silently skipped. The new
has_undecodable_rule() treats such a body as unreadable, so the gate
returns UNCONFIRMED (exit 1). The field is named with U+FFFD removed, so
a stray byte before "Disallow" cannot hide the line either. U+FFFD in a
comment or another field (Sitemap, Crawl-delay) stays harmless, and
valid UTF-8 non-ASCII rules decide as before.
Nine new tests in two FAIL-OPEN REGRESSION classes.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
* docs(changelog): record the robots_check BOM and U+FFFD fixes
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
---------
Co-authored-by: Can Mugan <217335573+canmugan@users.noreply.github.com>
Co-authored-by: Claude Opus 5.5 <noreply@anthropic.com>
_fetch() ran curl with text=True and no encoding, so Python decoded the
response with the Windows ANSI code page. On a byte that code page leaves
undefined (0x81 in cp1252 and cp1254, 0x9e in cp1254) subprocess's pipe
reader thread died, stdout came back None, rpartition() raised
AttributeError, and the gate printed "UNCONFIRMED (AttributeError)". That
fails closed, but it blocked the browser-header retry 09-web-research.md
permits on hosts such as tr.indeed.com (a UTF-8 CJK Disallow rule) and
kap.org.tr (a UTF-8 Turkish 404 page).
Pin encoding='utf-8', errors='replace' on the call (RFC 9309: robots.txt
is UTF-8), as verify_pdf.py and verify_layout.py already do. Decision
rules and the fail-closed handling of real read failures are unchanged.
The regression tests swap curl for a child process that prints the real
bytes, so the actual subprocess decode path runs with _fetch's own
kwargs, and pin cp1254 when no encoding is passed so a UTF-8 host cannot
pass the bug by luck. Both fail on master.
Co-authored-by: Can Mugan <217335573+canmugan@users.noreply.github.com>
Co-authored-by: Claude Opus 5.5 <noreply@anthropic.com>
