Background Fetch

[marcoscaceres]

Request for position on an emerging web specification

• WebKittens who can provide input: @annevk @youennf

Information about the specification

• Title: Background Fetch
• URL: https://wicg.github.io/background-fetch/
• GitHub repository: https://github.com/WICG/background-fetch/issues/
• Issue Tracker (if not the repository's issue tracker):
• Explainer (if not README.md in the repository): https://github.com/WICG/background-fetch#readme

See also https://developer.chrome.com/blog/background-fetch/.

Design reviews and vendor positions

• TAG Design Review: Background fetch w3ctag/design-reviews#279
• Mozilla standards-positions issue:

Bugs tracking this feature

• WebKit Bugzilla: https://bugs.webkit.org/show_bug.cgi?id=251980
• Radar: rdar://105213321

Anything else we need to know

An API to handle large uploads/downloads in the background with user visibility.

[dmurph]

@mkruisselbrink did a recent poke at WPT tests (and hopefully they can add more knowledge) and I think the summary was there are testing gaps around the various cross origin and CORS scenarios, so that would be a good area to focus some attention on.

[annevk]

I filed a number of issues on this in the past, which makes me concerned about maintenance:

• https://github.com/WICG/background-fetch/issues/created_by/annevk

(Some are addressed, but definitely not all.)

Apart from that I think the main concern here is the browser performing activity for the website while the end user is no longer visiting it. Even if you limit that up to the point where the end user switches networks, that would still reveal something about their activity. Potentially you could make this more visible through "download UI", but it's not immediately clear to me how that would work. Maybe a combination of a randomized time limit or the user switching networks, both enforced after closing the relevant tabs, could suffice?

I think there was tentative agreement that any script could run upon the next visit, but it would be good to confirm that is still the case.

[youennf]

I think there is a path forward with background fetch, in terms of browser UI, mitigations mentioned by Anne and the ability to postpone firing non user initiated events.

It would help if the spec would migrate to service worker WG.