[whatwg] RWD Heaven: if browsers reported device capabilities in a request header

Matthew Wilcox mail at matthewwilcox.com
Mon Feb 6 12:17:44 PST 2012

PS, sorry all if some mails here are duplicates. I am fighting my mail
client which keeps sending mail from the wrong account, which is then
rejected by the list.

On 6 February 2012 20:17, Matthew Wilcox <mail at matthewwilcox.com> wrote:

> On 6 Feb 2012, at 19:19, Bjartur Thorlacius wrote:
> > On Mon, 06 Feb 2012 18:58:00 -0000, Boris Zbarsky <bzbarsky at mit.edu>
> wrote:
> >> Again, it's not constant in the terms that the page sees, which are CSS
> pixels, not device pixels.
> >>
> > We're discussing HTTP here, so the content might just as well be raster
> bitmaps.
> Are we? Why, what makes HTTP the relevant factor? SPDY is the future and
> already supported in two major browsers., As it compresses headers and
> multiplexes, I don't see the issue.
> > Multiple and variable screen dimensions are quite common (in special for
> projection). That means a request for every screen the resource may be. For
> legacy HTTP servers that don't support the new and complicated
> If-Different-For-Device header that would have to be added would serve the
> same content once for every screen.
> No, it means we as a standards body define which gets sent. The sensible
> thing is to send the maximum screen size in use on the device.
> > So you have UAs sending extra headers with every request, making extra
> requests with even more extra headers in the fairly common case of variable
> screen dimensions (multiple screens) and either extra response headers for
> servers that use the feature (perfectly acceptable) and double round-trip
> lag (probably terrible) while the UA waits for the extra response header to
> check if there are alternative versions of the resource for differently
> sized screens and fetches the alternative version if there is one, or
> redundant fetching of *all* resources in proportion to the number of
> possible screen dimensions (assuming the best case of screen dimension
> being the only variable).
> Again, read the proposition I mentioned and you'll find non of this is
> true. Extra headers would only be sent by the browser if the browser
> received a request for the client to send those headers.

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