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Re: [libvirt] [PATCH v2 3/5] Extend nwfilter schema to accept comment attributes



On 09/28/2010 04:28 AM, Stefan Berger wrote:
okay.  It also leaves out 8-bit bytes - could that be a problem for i18n

where people want comments with native-language accented characters?
That is, are we being too strict here?  Maybe a better pattern would be
to reject specific non-printing ASCII bytes we want to avoid, assuing
you can use escape sequences like [^\001]?

Looking at

http://www.asciitable.com/

I should probably include 0x20-0x7E and 128-175, 224-238 - maybe even
more? So the regex then becomes

[ -~€-¯à-î]{0,256}

True ASCII is strictly 7-bit; any locale where isprint() returns true on 8-bit bytes is a superset single-byte encoding, such as ISO-8859-1, or 'extended ascii' from the URL you posted above. But I'm also thinking about multi-byte encodings, like UTF-8, where we cannot a priori write a regex that will accept all valid Unicode printable characters, in part because you have to look at more than one byte at a time to determine if you have a printable character. Which goes back to my suggestion of an inverse charset - rejecting bytes that are known to be non-printable ASCII, and letting everything else whether or not it is is a printable byte sequence in the current locale. So what about this idea: exclude control characters except for tab, and let space and everything after through (I don't know if it needs to be adjusted to also reject &#x00):

[^-&#x08&#x0A-&#x1F]{0,256}

--
Eric Blake   eblake redhat com    +1-801-349-2682
Libvirt virtualization library http://libvirt.org


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