Prefetching resources using SW

[mfalken]

This issue is for adding support to SW to prefetch resources during onfetch that it knows a controlled page will later request.

Imagine a page at www.example.com/foo/bar that has <image src="bar.png"> or does an XHR to www.example.net/bar. Currently the page must be fetched and parsed before the image or XHR fetch begins. It could be helpful if SW could prefetch the resources in the onfetch handler for "/foo/bar", and return the response (possibly an in-progress stream) in the onfetch handler for "bar.png" or /bar".

One idea is to use the cache for this:

// in onfetch for /foo/bar
cache.add('bar.png');
// in onfetch for bar.png
event.respondWith(cache.match('bar.png'));

But as currently spec'd, the .match call wouldn't succeed until the request initiated by the .add call completes.

Is there another way of supporting this use case?

[gavinp]

Isn't this a duplicate of issue 361?

[mfalken]

Yes looks like this is a particular use case that can be part of issue #361

[mfalken]

This looks the same as issue #573

[jungkees]

The .match promise in the example will resolve with an incumbent record, if there has been any, even before .add promise resolves. Or, if there has been no incumbent record, it will return the in-flight fetching record. The fulfillment of .add promise makes the resource be the new incumbent record for the next request.

Closing.