Consider relying on eTags (or other headers) for service worker dependencies to check for updates

[delapuente]

For the sake of modularization and isolation. Could it be possible to improve the update algorithm to rely on the eTag / content-size / other headers sent by the server to decide when a service worker changed? Now we need to include a mark of change in the sw and this forces a lot of developments to postprocess service worker files.

[annevk]

I think @ehsan and I had a proposal for this at some point.

[jakearchibald]

If the request is made with If-Modified-Since or If-None-Match, and the response is 200, we could assume this is a new SW even if it's byte identical. Although this would cause unnecessary service worker updates on servers that send out Etag or Last-Modified but don't correctly return 304.

Else we just add Service-Worker-Force-Update: 1 or something.

[delapuente]

More than checking if the main sw file changed, I'm referring to its dependencies imported via importScripts().

[jakearchibald]

Yep, understand that, you'd be sending an etag (or last-modified) that represented the SW and its dependencies.

Maybe that's too hacky?

[delapuente]

I think that undermines the purpose of the ETag about digesting the content being served. It would do the trick but I think is better to come up with something more pluggable in the actual ecosystem not requiring to hack with semantics. ;)

[jakearchibald]

Yeah, I think you're right. Service-Worker-Force-Update: 1 would work.

[jakearchibald]

I think we should have a JS API for this, reg.update({force: true}) perhaps.

[jakearchibald]

F2F: agreement on serviceworker.skipWaiting() and reg.update({force: true}) - but may need to look at naming of force.

Lots of problems using etags for this, eg if CDN stop serving etags for some reasons.

Rough idea around some-header-name: value where value is a digest like etags.

[jakearchibald]

reg.update({force: true}) will leave you with the existing worker if the update fails, as usual.

[annevk]

Was anyone able to dig up the previous proposal from @ehsan and I? I can't find it.