Re: detecting connection speed

On Wed, Dec 11, 2013 at 7:36 PM, Nic Jansma <nic@nicj.net> wrote:

> One of the reasons ResourceTiming v1 didn't expose bytes transferred was
> due to cross-origin security concerns, eg. detecting if a user had already
> downloaded a known image from a separate site mybank.com.  I would assume
> that is still a security concern, and it may limit the usefulness for some
> of the use-cases presented if they involve other origins.
>
> I hadn't seen cross-origin limitations brought up, so I wanted to make
> sure everyone that was discussing this was aware of the issue.
>
> Here's a thread from last year that discussed byte-size a bit:
> http://lists.w3.org/Archives/Public/public-web-perf/2013Jan/0000.html


I don't follow the reasoning behind limiting this information for
third-party origins -- can someone elaborate? First, we already require
that third-party resources must opt-in into ResourceTiming via an
additional header, and second, I would posit that anything you can "infer"
about the user via bytesize is equally guessable via timing the resource
itself... and we've already elaborated on that in the privacy section [1].

[1] http://www.w3.org/TR/resource-timing/#privacy-security