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Rudick, Tom a écrit :
> If the HTTP headers do not indicate what the encoding of the document
> is, you must read the document (at least the first line) and figure out
> what the encoding is. However, how is this accomplished? If you don't
> know the encoding of the document to begin with, how can you read even
> the first line?
>
> After reading this http://www.w3.org/TR/REC-xml/#sec-guessing, it seems
> that instead of reading what <?xml encoding="utf-8"?> has to say,
> parsers simply look at the first few octets of the document and compare
> it to several known encodings of the text <?xml. Then, they just
> continue to read the rest of the document.
Not exactly : the first few octets will indicate if <?xml
encoding="blah-blah"?> is coded on 1, 2, or even 4 bytes (for UCS) ; the
charset of the sequence <?xml encoding="blah-blah"?> is limited to
ASCII-7 bits, which is fortunately compatible with UTF-8, ISO-8859-1 and
some others, and easily decodable if coded on 2 or 4 bytes, because the
same sequence is mapped to ASCII-7 bits, whatever the number of bytes
(zero-extension) ; for example :
Bits Encoding Hex Dec Char
7 US-ASCII 41 65 A 1000001
8 ASCII 8bits 41 65 A 01000001
16 UCS-2 41 65 A 00000000 01000001
32 UCS-4 41 65 A 00000000 00000000 00000000 01000001
So, the encoding can be read (if any)
I guess some parsers have additional heuristics for reading successfully
the sequence <?xml encoding="blah-blah"?> ; maybe some try-catch to
apply with the set of charset they know ?
--
Cordialement,
///
(. .)
--------ooO--(_)--Ooo--------
| Philippe Poulard |
-----------------------------
http://reflex.gforge.inria.fr/
Have the RefleX !
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