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Re: UTF-8 Encoding Question

From: John Glavin <john@riverfrontsoftware.com>
Date: Wed, 28 Feb 2001 22:57:05 -0800
Message-ID: <000c01c0a21c$d3fed090$0c77b2d1@win2k>
To: "Greg Stein" <gstein@lyra.org>, "John Glavin" <john@riverfrontsoftware.com>
Cc: <w3c-dist-auth@w3.org>
Thanks, this makes sense now.  I guess what I can do is see if the URI
contains a valid UTF-8 sequence and if it does then assume it's UTF-8
encoded.  I got the following text from RFC-2279

UTF-8 strings can be fairly reliably recognized as such by a
      simple algorithm, i.e. the probability that a string of characters
      in any other encoding appears as valid UTF-8 is low, diminishing
      with increasing string length.

Webfolders must be doing something similar to this since it understands both
UTF-8 and Latin-1.

John Glavin
RiverFront Software
john@webdrive.com
http://www.webdrive.com


----- Original Message -----
From: "Greg Stein" <gstein@lyra.org>
To: "John Glavin" <john@riverfrontsoftware.com>
Cc: <w3c-dist-auth@w3.org>
Sent: Wednesday, February 28, 2001 4:54 PM
Subject: Re: UTF-8 Encoding Question


> We just had a discussion related to this on mod_dav's mailing list.
>
> On Wed, Feb 28, 2001 at 03:52:37PM -0800, John Glavin wrote:
> >...
> > But I run into a problem with the mydocsonline.com DAV server which says
> > it is using UTF-8 Encoding but returns the href as href: Magn%FCs.txt
> > This is not UTF-8 encoded, because characters > 0x80 in UTF-8 will be
> > encoded in a multibyte sequence.  This is normal ISO-8859 (Latin)
Encoding.
>
> There are two references to UTF-8 in the response: the Content-Type header
> and the XML document header:
>
>     Content-Type: text/xml; charset="utf-8"
>     <?xml version="1.0" encoding="utf-8"?>
>
> Both of these refer to the *response body*. In that sense, all characters
in
> the body are properly UTF-8 encoded.
>
> The URL itself is in its "escaped" form. See sections 2.4.2 of RFC 2396
for
> more info. Section 2.1 covers the general problem of UTF-8 encodings for
> URLs.
>
>
> To be more concrete. Section 2.1 defines two types of characters: "URI
> characters", and "original characters". The "utf-8" above refers to the
URI
> characters since that is what is sitting in the body of the response.
>
> The % escaping will give you a set of octets. The question then becomes,
> "what encoding will transform those octets into the 'original'
characters?"
> At the moment, you do not have enough information to do that. There is no
> attribute or header or other item that you can inspect for that.
>
> > In this case I am not sure what to do.  I use the Windows API call
> > MultiByteToWideChar function but I need to tell it to use either UTF-8
or
> > ANSI code pages.  For the mydocsonline server I need to use ANSI however
> > they are telling me to use UTF-8 and using UTF-8 wont work.
> >
> > When I use Webfolders it works properly on the mydocsonline server and
> > somehow knows to not use UTF-8 decoding.  Does anyone have any idea why
it
> > works or how I could really detect which code page to use ?
>
> I think your statement about it "working" for some servers, and not
working
> for mydocsonline (which is based on an early mod_dav; the current mod_dav
> has the same issue, tho) is based on a presumption that the character set
> for the URI characters == the charset of the original characters. That
> assumption is being made by servers and clients today.
>
> In mod_dav's case, we take the URI's (unescaped) octets and simply save
the
> resource under that name. We then return it using the same octet sequence
> (properly escaped). The net effect is that we keep the same encoding of
the
> "original characters" for the client. Of course, the problem arises when
one
> client saves using a UTF-8 encoding and another reads as Latin-1.
>
> But mod_dav does not have enough information from the client to decode the
> URL into (say) Unicode, and save that. If it could, then we could always
> return a UTF-8 encoding for the original characters (although we would
still
> have no way to tell that encoding to the client; clients would just
continue
> to assume the response encoding matches that encoding and it would
*happen*
> to match).
>
>
> To be really clear, let's go with a little diagram here:
>
>     Unicode resource name ("original characters")
>        |
>      [ UTF-8 encoding ]
>        |
>     URI octet sequence
>        |
>      [ URI %-escaping ]
>        |
>     Returned URI ("URI characters")
>
> But another totally legal scenario is:
>
>     Latin-1 resource name ("original characters")
>        |
>      [ identity (no) encoding ]
>        |
>     URI octet sequence
>        |
>      [ URI %-escaping ]
>        |
>     Returned URI ("URI characters")
>
> There is nothing in the response body to indicate which of the above two
> forms is occurring. Similarly, there is nothing in the request body to
> indicate which was used for the Request-URI. Because of the latter,
servers
> are just as broken if they make an assumption about how to decode from the
> URI octets into original characters.
>
> mod_dav does not attempt to decode/encode between octets and original
> characters. It just keeps them as octets. But that does imply that the
> encoding used by the client when it stored the resource better be the same
> encoding used when accessing the resource and the same decoding used for a
> PROPFIND result.
>
> RFC 2396, section 2.1 explicitly punts this issue to a future date. It
seems
> that I recall an internet draft, or even possibly a new RFC, but I'm not
> immediately aware of it.
>
> Cheers,
> -g
>
> --
> Greg Stein, http://www.lyra.org/
Received on Thursday, 1 March 2001 01:48:09 GMT

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