[Varnish] #259: support for revalidating with 304, support for user-reloading

[Varnish]

#259: support for revalidating with 304, support for user-reloading
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 Reporter:  ebik         |       Owner:  phk  
     Type:  enhancement  |      Status:  new  
 Priority:  normal       |   Milestone:       
Component:  varnishd     |     Version:  trunk
 Severity:  normal       |    Keywords:       
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 I would like to have possibility to 'invalidate' page in 'vcl_hit'. I.e. I
 want to reload the page from backend if I think the page is invalid (e.g.
 by some hint that browser sends to me [this can be used to DOS attack, but
 use of such feature is administrator's decision]).

 Next level is to have ability to 'revalidate' page from backend. I.e. I
 would like to send etag and/or last modified time from varnish to backend,
 which will be able to response with 304 not modified. This should be
 alternative to 'discard' option in 'vcl_discard' but it should be also
 available in 'vcl_hit' instead of 'invalidating' proposed above.

 And the most advanced stuff will be possibility to run the revalidation in
 background, i.e. return old page and request revalidation from backend at
 the same time, both by 'GET' or by 'HEADER' request.

 This will give the possibility to have page, e.g., 30 seconds in cache in
 'authoritative' way and next 5 minutes in 'unauthoritative' way (with
 revalidating from server) and then discarding.

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Ticket URL: <http://varnish.projects.linpro.no/ticket/259>
Varnish <http://varnish.projects.linpro.no/>
The Varnish HTTP Accelerator