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RE: Webtrends HTTP Server %20 bug
From: Glynn Clements <glynn.clements () virgin net>
Date: Fri, 8 Jun 2001 04:51:57 +0100


Eric Hacker wrote:

Unicode is a superset of ACSII and thus all ASCII characters are Unicode.
UTF8 is a way of encoding unicode code points for transport over the
internet in a restricted character set. Conveniently, UTF8 uses the same
values as ASCII for ASCII representation. Above the standard ASCII 127
character representation, UTF8 uses multi-byte strings beginning with 0xC1.

No; the sequences for codes 128 to 255 begin with 0xC2 and 0xC3
(128-191 and 192-255 respectively). 0xC0 and 0xC1 indicate (illegal)
overlong encodings of 0-63 and 64-127 respectively.

In general, the two-byte sequences have the (binary) form:

   110xxxxx 10xxxxxx

The range 0-127 (which must use the single-byte form instead)
corresponds to:

   1100000x 10xxxxxx

Hence, any sequence beginning with 11000000 (0xC0) or 11000001 (0xC1)
is illegal.

-- 
Glynn Clements <glynn.clements () virgin net>


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