[webkit-dev] X-Purpose on prefetching requests

Alexey Proskuryakov ap at webkit.org
Tue Sep 28 17:04:23 PDT 2010

28.09.2010, в 16:16, Adam Barth написал(а):

> I guess I don't understand your perspective.  Are you arguing that
> prefetch is a misfeature and folks should use image tags instead?
> That doesn't really make sense to me.  For example, using an explicit
> prefect API means the prefetch gets properly prioritized and doesn't
> delay the load event.

This wasn't a preconceived idea of mine when starting this discussion. However, I'm actually beginning to think that cross-origin prefetch may be a misfeature indeed. It's one thing to optimize one's own site loading, and another to use someone else's bandwidth. The effects this has on statistics and network monitoring are secondary reasons to doubt that this is a good idea.

The benefit of cross origin prefetching seems to be limited, too. In most cases, you can only prefetch the main resource, which likely requires revalidation anyway.

>  Below you characterize prefetch as a hack, but
> it seems like a useful feature that's used by a bunch of sites.
> As for X-Purpose, sometimes you seem to be saying that it can't be
> used correctly, whereas other times you seem to be saying that it can
> be used correctly, just that sites will screw it up.  At the beginning
> of the discussion, you seemed worried about the size increase to
> requests.  Reading your messages, it feels like you don't like
> X-Purpose, but you're not quite sure why.  As the discussion
> progresses, your reasons for disliking it seem to shift.

Yes, this is a correct impression. I'm not sure why you look at this as something negative. I didn't know about the consequences of link prefetch much in the beginning, and reacted to this patch simply because it smelled wrong (disclose more information without saying a word about why that's beneficial, and why it's not dangerous). The new arguments that are being provided are worth answering, and it's only fair that each gets its own answer.

Others have also noticed that there were major questions that weren't answered in <https://bugs.webkit.org/show_bug.cgi?id=46529>, or in any discussion linked from it.

> Server operators seem to be sad that we're don't have the same feature
> as Firefox.  I don't understand why we shouldn't make them happier.

This is a good argument for spending time on designing a feature, not necessarily so for shipping it.

- WBR, Alexey Proskuryakov

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