RE: Web browsers, HTTP and transcoding

No. The implications don't go both ways. I was pointing out that a mobile application using Ajax that wants to be immune from interference from an intermediary CT will need to use a payload format that is unlikely to be of interest to the CT. A text/plain payload should do the trick, if the app developer is assuming the CT only looks at the MIME type and won't take an interest in text. If you know that CTs won't manipulate an XML payload that doesn't look like a page, then you can use XML MIME types too. If CTs assume all XML MIME types are adaptable, then you're in trouble with that format.

However, from the CT perspective you have the problem of trying to distinguish between a normal browser request and a request via XHR, where it is likely that the implementer of the Web application didn't take any action to avoid interference from CT proxies.

In this case, you might try to be more clever and keep track of the MIME type of the previous request (in the same session?) of the the device and look for unusual shifts between markup types. You could sniff the beginning of the page to see if it really is a page, or just a fragment, or some crazy invented XML language. There's no easy answer when you're a CT and trying to deal with XHR apps that didn't anticipate your presence.

It would certainly be nicer if XHR flagged itself in the UA, but I think we're too late.

---Rotan





From: Tom Hume
Sent: Fri 17/10/2008 00:02
To: Rotan Hanrahan
Cc: public-bpwg-ct
Subject: Re: Web browsers, HTTP and transcoding


Does this imply that transcoding proxies shouldn't transcode items of content with MIME types that is "text/xml, application/xml or ends in +xml (ignoring any parameters)" (the ones referred to in the XHR standard)? 


On 16 Oct 2008, at 23:51, Rotan Hanrahan wrote:


In these scenarios, mobile Ajax should stick to raw text, XML or JSON as a payload format. If it is communicating with fragments of HTML and you've already adapted (or otherwise "enhanced") the page in which the Ajax is operating, the chances of that fragment of HTML being of any use any more (adapted or not) are significantly diminished already.

Good point about the UA though. I must double-check.


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