Bug 60493

Summary: ApplicationCache - feature request for a way to override the fallback behavior
Product: WebKit Reporter: Michael Nordman <michaeln>
Component: WebCore Misc.Assignee: Nobody <webkit-unassigned>
Status: NEW ---    
Severity: Normal CC: ap
Priority: P2    
Version: 528+ (Nightly build)   
Hardware: Unspecified   
OS: Unspecified   

Description Michael Nordman 2011-05-09 12:10:37 PDT
Application Cache - feature request for a way to override the fallback behavior

This is a feature request from a team using the appcache for offline support. They're looking for a means of not invoking the fallback resource for some error responses that would generally result in the fallback resource being returned. An additional response header would suite they're needs... something like...

  x-webkit-appcache-fallback-override: disallow-fallback

If a header was present with that value, the fallback response would not be returned.
Comment 1 Alexey Proskuryakov 2011-05-09 15:17:11 PDT
This sounds like something to discuss on HTML WG mailing list. But some more information about the use case would be nice to have - it sounds like the desire is to abuse error responses to pass real information, which is not necessarily so great.
Comment 2 Michael Nordman 2011-05-09 16:48:12 PDT
The app has a broad fallback namespace and there is a handler to handle the case when the server is not reachable. But this handler also gets triggered when the server is reachable in cases where the error is legitimate and should be delivered to the caller. So they've requested a means of tagging responses such that they won't trigger the fallback response.

For example lets say the server response is a 404 along with a page that explains the object being accessed was deleted. Instead of seeing a page that sayz "you must be offline, try again when online", that error page should come thru as is.
Comment 3 Michael Nordman 2011-05-09 16:55:35 PDT
There's a seperate bug open for this in the chromium project.
http://codereview.chromium.org/6969006/
Comment 4 Alexey Proskuryakov 2011-05-09 19:16:32 PDT
I think that this is a reasonable scenario. Still, a mailing list discussion seems like a pre-requisite.
Comment 5 Michael Nordman 2011-05-09 22:32:39 PDT
Yup, I'll ping the whatwg list with this feature request. I've filed this bug in the interest of feature parity and leaving an audit trail to that end.

A change along these lines in headed for chrome12 (beta this week). The name of the header/value pair that overrides the fallback handling in chrome12 is...

   x-chromium-appcache-fallback-override: disallow-fallback