There's a proposal at https://github.com/jakearchibald/background-cache
for enabling persistently-tracked uploads/downloads in the background.
It might change names to background-fetch.
I'm interested in getting some informed feedback about the following
use-case on https://github.com/jakearchibald/background-cache/issues/3
A motivating use-case is for a site that wants to download
movies/podcasts in the background and keep them around for offline
purposes. Once the file is downloaded, it seems clear that the
(ServiceWorker [DOM]) Cache API[1] is a great place to store the
result. What's less clear is how best to handle allowing the user to
begin watching the movie when the download is still in-progress. A
potential straw-man is:
* Start the download with background-fetch
* Use the background-fetch API to track the status of the download.
When there's "enough" downloaded, start playing the video via its online
URL with the confidence that the netwerk cache2 can unify the two
requests as much as possible.
* When the download completes, stick the movie in the DOM Cache API and
use Cache-furnished Responses for all future playback requests.
The greatest concern right now is around range requests and redundantly
downloaded data. We've seen interest in the Service Worker repo issues
for the ability to track/match in-flight fetch requests[2] that I hope
should be entirely mooted by the HTTP cache. Depending on the HTTP
cache until the download is complete ideally avoids redundant downloads,
but it would be great to have reassurance and an understanding of how a
background-fetch download mechanism might interact with the HTTP cache.
Could the download entirely use the HTTP cache for storage with the
cache entries pinned to avoid eviction until the download notification
extendable event completes?
Andrew
1:
https://w3c.github.io/ServiceWorker/spec/service_worker/index.html#cache-objects
2: https://github.com/w3c/ServiceWorker/issues/959
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