Re: HEX-UTF-8 vs. Unicode-escapes (was Re: [EAI] Re: utf-8-address syntax: ...)

["Charles Lindsey" <chl at clerew.man.ac.uk>]

On Mon, 26 Feb 2007 23:27:29 -0000, Chris Newman <Chris.Newman at Sun.COM>  
wrote:

> Good question.  I would have preferred to use xtext, but this text from  
> RFC 3461 makes that not possible without too much risk of breakage:
>
>    Due to limitations in the Delivery Status Notification format, the
>    value of the original recipient address prior to encoding as "xtext"
>    MUST consist entirely of printable (graphic and white space)
>    characters from the US-ASCII [4] repertoire.  If an addr-type is
>    defined for addresses which use characters outside of this
>    repertoire, the specification for that addr-type MUST define the
>    means of encoding those addresses in printable US-ASCII characters
>    when are then encoded as xtext.
>
> The problem is that xtext is a transfer encoding which is removed when a  
> traditional message/delivery-status part is generated and there's a hard  
> requirement in today's deployed MTAs that the result of xtext removal be  
> 7-bit ASCII.

Ah! I had not appreciated that the xtext had to be unscrambled when it was  
put into a message/delivery-status. So they force us into a double  
encoding.

All right, suppose we use %HEX for the utf-8, and we have a local-part
    <esc>Aa+å
then it becomes
    %1BAa%2B%C3%B8
which then has to be encoded into <xtext>, which turns out to be a Null  
transformation. I suppose that is as good as we are going to get.

The problem arises, of course, because delivery status was made (quite  
wrongly) to be a message type, and you are not allowed to C-T-encode  
message types. Really, one or other of those decisions needs to be  
reversed, but that is not so easy.

> So xtext was badly botched.

Indeed so.

--
Charles H. Lindsey ---------At Home, doing my own thing------------------------
Tel: +44 161 436 6131 ;                      
   Web: http://www.cs.man.ac.uk/~chl
Email: chl at clerew.man.ac.uk      Snail: 5 Clerewood Ave, CHEADLE, SK8 3JU, U.K.
PGP: 2C15F1A9      Fingerprint: 73 6D C2 51 93 A0 01 E7 65 E8 64 7E 14 A4 AB A5

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