[jira] [Commented] (TS-4829) Via: header string should not be cached

["Miles Libbey (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/TS-4829?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15475981#comment-15475981 ] 

Miles Libbey commented on TS-4829:
----------------------------------

The node caches the Via header from its parents. It then appends its information to the end of the string.

Examples:

Via: http/1.1 4th_parent.example.com (ApacheTrafficServer/6.2.1 [uScMsSfWpSeN:t cCMi p sS]), http/1.1 3rd_parent.example.com (ApacheTrafficServer/6.2.1 [uScMsSf pSeN:t cCMi pSs ]), http/1.1 2nd_parent.example.com (ApacheTrafficServer/6.2.1 [uScMsSfWpSeN:t cCMi pSs ]), http/1.1 1st_parent.example.com (ApacheTrafficServer/6.2.1 [uScHs f p eN:t cCHi p s ]), http/1.1 child.example.com (ApacheTrafficServer/6.2.1 [uScMsSf pSeN:t cCMi pSs ])

This was: 
1) miss on child.example.com.
2) hit on 1st_parent.example.com

(then purged 1st_parent.example.com)

Via: http/1.1 4th_parent.example.com (ApacheTrafficServer/6.2.1 [uScMsSfWpSeN:t cCMi p sS]), http/1.1 3rd_parent.example.com (ApacheTrafficServer/6.2.1 [uScMsSf pSeN:t cCMi pSs ]), http/1.1 2nd_parent.example.com (ApacheTrafficServer/6.2.1 [uScHs f p eN:t cCHi p s ]), http/1.1 1st_parent.example.com (ApacheTrafficServer/6.2.1 [uScMsSfWpSeN:t cCMi pSs ]), http/1.1 child.example.com (ApacheTrafficServer/6.2.1 [uScMsSf pSeN:t cCMi pSs ])

This was: 
1) miss on child.example.com.
2) miss on 1st_parent.example.com
3) hit on 2nd_parent.example.com

Via: http/1.1 4th_parent.example.com (A pacheTrafficServer/6.2.1 [uScMsSfWpSeN:t cCMi p sS]), http/1.1 3rd_parent.example.com (ApacheTrafficServer/6.2.1 [uScMsSf pSeN:t cCMi pSs ]), http/1.1 2nd_parent.example.com (ApacheTrafficServer/6.2.1 [uScHs f p eN:t cCHi p s ]), http/1.1 1st_parent.example.com (ApacheTrafficServer/6.2.1 [uScRs f p eN:t cCHi p s ]), http/1.1 child.example.com (ApacheTrafficServer/6.2.1 [uScRs f p eN:t cCHi p s ])

(then fetched a ton from child.example.com)

This was: 
1) hit on child.example.com.
(while 1st_parent.example.com said it was a cache hit, it did not go to that machine)

> Via: header string should not be cached
> ---------------------------------------
>
>                 Key: TS-4829
>                 URL: https://issues.apache.org/jira/browse/TS-4829
>             Project: Traffic Server
>          Issue Type: Bug
>            Reporter: Miles Libbey
>
> We use a cache hierarchy.  In theory the Via: string shows the path the request took through proxies, and with proxy.config.http.insert_response_via_str set to 3, a lot of info is presented -- cache hit, etc. (The Via header is described in 
> https://www.w3.org/Protocols/rfc2616/rfc2616-sec14.html#sec14.45)
> However, the string is cached, so it doesn't accurately reflect the path that *this* request took. Instead, it shows the path of the original request.
> For instance, imagine 2 servers, conveniently named child.example.com and parent.example.com, which also represents their roles in the cache hierarchy. The object is cacheable for a long time.
> The first request for the object might look like:
> Via: http/1.1 parent.example.com (ApacheTrafficServer/6.2.1 [uScMsSfWpSeN:t cCMi p sS]), http/1.1 child.example.com (ApacheTrafficServer/6.2.1 [uScMsSf pSeN:t cCMi pSs ])
> (with the cM meaning cache miss). The second request, a cache hit that just goes through child.example.com might show:
> Via: http/1.1 parent.example.com (ApacheTrafficServer/6.2.1 [uScMsSfWpSeN:t cCMi p sS]), http/1.1 child.example.com (ApacheTrafficServer/6.2.1[uScHs f p eN:t cCHi p s ])
> eg, cache Hit for child, but cache Miss for parent -- even though the parent wasn't involved in the request, and, if it were, it would be a Hit.  The parent portion was cached by child.example.com.
> The expected behavior is that the 2nd request would yield:
> Via: http/1.1 child.example.com (ApacheTrafficServer/6.2.1[uScHs f p eN:t cCHi p s ])



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