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

[Matthew Wilcox]

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.