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Re: ACTION-961: usefulness of multipart-mixed

From: Luca Passani <passani@eunet.no>
Date: Tue, 26 May 2009 23:49:12 +0200
Message-ID: <4A1C63D8.9060606@eunet.no>
To: Mobile Web Best Practices Working Group WG <public-bpwg@w3.org>

Multipart was a useful mechanism to deliver a full page in one shot. 
Vodafone leveraged multipart for its vodafone live service on devices 
which supported it. Multipart allowed for snappy (or at least 
"2002-snappy") display of the top page, which looked great as compared 
to everything WAP had represented until that day.
There was no way to know whether multipart was properly supported by a 
device, except testing on that device. Notably, many devices declared 
multipart support in headers and UAProfs, but the information was not 
reliable at all. I recall that I never managed to get multipart to work 
on a Nokia device (still vaguely curious about whether there was a way).
Vodafone maintained its own db with this info for devices in its 
portfolio. Not sure if they still do. Probably not. Too much effort for 
too little value.

3G networks and faster browsers make the use of multipart much less 
relevant, particularly because pages become much harder to build and 
maintain if multipart is in the middle. I made space for multipart in 
WURFL back in 2003, but the community did not really follow: nobody was 
using it obviously.


Tom Hume wrote:
> I took an action a couple of weeks ago to look into multipart/mixed 
> MIME types, to see if they might
> be usefully related to sections 3.4.6 and 3.4.7 of MWABP[1] 
> (ACTION-961). In particular it would seem
> helpful to be able to bundle many images up into a single HTTP 
> request, avoiding unnecessary round
> trips to download a set of them. The current advice is to combine 
> related images into a single
> file, download this, and use CSS positioning and clipping to render 
> parts of this file. multipart/mixed
> would provide another route for downloading many resources at once.
> The only reference I can find to mobile usage of multipart-mixed is 
> this tutorial from OpenWave:
> http://developer.openwave.com/dvl/support/documentation/technical_notes/multipart.htm
> From running this experiment with desktop browsers, multipart-mixed 
> doesn't seem to be well
> supported. I've set up an HTTP response matching the above and found that:
> - Firefox and Opera render the second page in the message
> - Safari doesn't recognise it as HTML and downloads it
> - IE renders content from both pages
> I've also got a question of how, from within CSS or similar, an 
> individual part of a multipart-mixed
> message might be uniquely referred. The only reference I can find for 
> a URL-scheme for such
> things is a scheme for references to body parts of messages, which 
> date back to 1997 or earlier,
> and seem to be designed with HTML email in mind: 
> http://www.ietf.org/rfc/rfc2392.txt
> Beyond the Openwave tutorial, and the following tool which exists to 
> create these messages:
> http://www.umts-tools.org/docs/multipart/
> ...I can't find any other reference to them; and it's not a technique 
> I've come across myself. Am
> I missing something obvious here? From where I'm sitting this looks 
> like a barely-used, poorly-
> supported technique which I'd hesitate to consider a best practice - 
> though it might be handy if
> it worked.
> Tom
> [1] http://www.w3.org/TR/2009/WD-mwabp-20090507/#d1e8981
> -- 
> Future Platforms: hungry and foolish since 2000
> work: Tom.Hume@futureplatforms.com 
> <mailto:Tom.Hume@futureplatforms.com> play: tomhume.org 
> <http://tomhume.org>
Received on Tuesday, 26 May 2009 21:49:53 UTC

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