Tighten UTF-8 validity checks.
------------------------------
Key: LUCY-179
URL: https://issues.apache.org/jira/browse/LUCY-179
Project: Lucy
Issue Type: Improvement
Components: Util
Reporter: Marvin Humphrey
Fix For: 0.3.0 (incubating)
Lucy currently outsources UTF-8 validity checking to the Perl C API function
is_utf8_string(). This suffices for sanity checking of basic byte sequences
and detecting non-shortest-form, but since is_utf8_string() only validates to
the loose Perl internal "utf8" format[1], it allows through certain constructs
we should probably thwart: UTF-8 coded UTF-16 surrogates (both paired and
isolated), and code points above 0x10FFFF.
Since Lucy is not an application but rather a library, we should continue to
pass through "noncharacter" code points which are discouraged for "public
exchange"[2] but are allowed for internal application use, such as U+FFFF.
(Such code points may be useful as e.g. sentinels or separators). These code
points will be allowed to end up in indexes; it will be the responsibility of
the application to filter them at input or output.
[1] http://perldoc.perl.org/Encode.html#UTF-8-vs.-utf8-vs.-UTF8
[2] http://www.unicode.org/versions/Unicode6.0.0/ch03.pdf section 3.2, clause C2
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