Web browsers, HTTP and transcoding

Folks

One thing that came up in the last CT group call was the notion that  
applications other than browsers might make use of HTTP and thereby  
might be affected by transforming proxies.

As Jo pointed out, the CT document is explicit that its scope is for  
browsing only. However there are instances where a browser might make  
HTTP requests which are not for any markup and therefore should not be  
transcoded; for instance, requests triggered by an XmlHttpRequest  
implementation as part of a mobile AJAX service.

Section 4.1.3 says that

> The mechanism by which a proxy recognizes the user agent as a Web  
> browser should use evidence from the HTTP request, in particular the  
> User-Agent and Accept headers.

In this case, a user agent which is a web browser may nonetheless be  
using HTTP GET and POST requests to request content which should not  
be transcoded. I'm not sure the user agent can be used to disambiguate  
AJAX HTTP from "regular" browser, and a look through the W3C  
XMLHttpRequest standard[1] doesn't show any reference to an  
alternative User Agent being used, and refers (in section 4) to the  
responses of AJAX calls potentially having a text/html MIME type - so  
that can't be used either.

Are there considerations around mobile AJAX here - something which may  
not be prevalent right now, but could be expected to become more so  
over time? Apologies in advance if I have let out some worms.

Tom

[1] http://www.w3.org/TR/XMLHttpRequest/#send

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