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From "Jon Moore (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HTTPCLIENT-1032) cache revalidation of variants does not update original variant entry
Date Thu, 09 Dec 2010 16:58:01 GMT

    [ https://issues.apache.org/jira/browse/HTTPCLIENT-1032?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12969807#action_12969807

Jon Moore commented on HTTPCLIENT-1032:

I think this is related to the way we store and manage variants. Right now, we create a cache
key for a variant based on the varying headers from the original request, and then store these
cache keys on the "parent" entry. I think this combines two items which should be separated:

1. which cache entries are variants of a parent entry
2. which variant should be used for a particular set of request headers

I think this might be as simple as turning the Set<String> "variantURIs" on the parent
cache entry into a Map<String,String> that maps request header values (using the scheme
we currently use to generate the variantURI cache keys) to particular cache locations. Thus
in the example above, rather than storing a new variant entry, we should simply "point" requests
with "User-Agent: agent2" to the cache entry for the "agent1" response.


> cache revalidation of variants does not update original variant entry
> ---------------------------------------------------------------------
>                 Key: HTTPCLIENT-1032
>                 URL: https://issues.apache.org/jira/browse/HTTPCLIENT-1032
>             Project: HttpComponents HttpClient
>          Issue Type: Bug
>          Components: Cache
>    Affects Versions: 4.1 Beta1
>            Reporter: Jon Moore
>            Priority: Minor
>         Attachments: variant-entry-update-test.patch
> When the cache stories multiple variant entries due to Vary headers in responses, the
cache correctly sends a conditional request containing the etags of any existing variants
on a "variant miss" (incoming request does not match the request variants already cached).
In addition, when it receives a 304 response, it correctly returns the indicated variant to
the request that causes the variant miss. However, it does not update the pre-existing variant
cache entry as recommended by RFC 2616.
> For example:
> request 1, User-Agent: agent1 results in a 200 OK with Etag: etag1 and Vary: User-Agent.
> request 2, User-Agent: agent2 causes an If-None-Match to the origin; if it returns 304
Not Modified with Etag: etag1
> request 3, User-Agent: agent1 results in a 200 OK but gets the (outdated) entry that
resulted from request 1
> in other words, the origin response from request 2 does not update the variant for "agent1".
> This does not cause incorrect behavior (this is a SHOULD) but does miss out on some caching
opportunities here.

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