Mobile Web Best Practices Working Group News

There were a few posts [*] over the last few weeks about content transformation, and it's been some time since we launched the Content Transformation Task Force within the Mobile Web Best Practices Working Group and published a working draft of the Content Transformation Landscape document. Time for an update!

The Task Force has been working ever since on a Content Transformation Guidelines document. It's still a draft, but we should publish it as First Public Working Draft in a couple of weeks. What does the document contain so far?

HTTP headers spoofing: in an ideal world, there would be no need to change the User-Agent header whatsoever. But many legacy web sites actually return an HTTP 200 response with a: "Sorry, I don't know who you are" message when requested with a User-Agent they don't know anything about. Such sites are typically good candidates for content adaptation, and there's no other way for the transcoding proxy to get a meaningful response than to behave as a "desktop" browser...

The guidelines currently recommend a two-step approach:

• Send the original HTTP request to the server.
• If the response from the server is a "Sorry, I don't know who you are" response, then try again with a modified HTTP request, possibly changing the User-Agent in particular to whatever is needed to get a response.

With that approach, the content provider receives the original request, and the transcoding proxy still is able to handle the "Sorry, I don't know who you are" case.

Control by the content provider: use a "Cache-Control: no-transform" directive to tell the transcoding proxy not to perform any transformation. Use a "Vary" HTTP header to tell the transcoding proxy that they vary their presentation based on the User-Agent for instance.

Transcoding proxy's decision to transform: the "link" element, labeling using POWDER would be the best way to say "I'm mobile". There's no easy answer in the generic case. Page size, URI patterns, content type are examples of criteria to consider.

Feel free to subscribe/take a look at/send comments to the Content Transformation Task Force mailing-list, it's public!

[*] A few recent posts on content transformation:

• Dennis' Sprint OpenWeb Update
• Luca Passani's Rules for Responsible Reformatting
• Dennis' How Web to Mobile Transcoding Should Work
• Tom Hume's Mobile transcoding guidelines