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[Reference:<_A1700@delegate-en.ML_>]
Newsgroups: mail-lists.delegate-en

[DeleGate-En] Re: refresh file on a cache
18 Jun 2002 22:04:47 GMT "michel.guilhem" <pradabdyi-bkxfmxllazxr.ml@ml.delegate.org>
annuwave.net


Le Mardi 18 Juin 2002 23:01, vous avez écrit :
Thank you for the response , i think that i develop a script to detect on a 
origin server the changes .
I put the changes on the directory of my delegate , restart this with 
expire=0 and do a ls -l on the subdirectory changed .
then restart with expire=1d .
With this manner i realize a push .
But this push needs access to the origin server and to the delegate .


> Hi,
>
> On 06/09/02(17:30) you michel <pradabdyi-bkxfmxllazxr.ml@ml.delegate.org> wrote
> in <_A1678@delegate-en.ML_>
>
>  |>  |How to be sure that a file on the delegate cache is fresh like the
>  |>  | same file on a server ?
>  |>
>  |> EXPIRE=0
>  |>
>  |> will do.  With this, on each request from client, DeleGate always
>  |> (0 seconds after the data is cached) asks the server if the cached
>  |> data is fresh or no (using If-Modified-Since header).
>
> This works when a HTTP client accesses to a HTTP server via DeleGate
> as a HTTP proxy, because the mechanism "If-Modified-Since" (do real
> transfer only when the original data is modified since the data is cached)
> is an inherent one in the HTTP protocol to achieve what you (and everyone)
> need.  See RFC2616.
>
>  |I'm a newbie , my question is basic but i'm blocked by this .
>  |Please help me , i have to defend Delegate's solution in my organisation
>  |and the first step is to responds to this demand (with a ftp - or http -
>  |cache tree structure , how to be sure that the files modifications are
>  |propagating immediately and only this , the others files , not modified
>  |  , reached on the proxy ) .
>
> Unfortunately, there is no such mechanism in FTP protocol as in HTTP
> to help caching.  Original protocol does not support method to get
> meta-information like file size nor its modified time.  See RFC959.
> Recent extensions added "SIZE" (get file size) and "MDTM" (get modified
> time).  FTP-proxy DeleGate uses these command to suppress unnecessary
> transmission of PLAIN file data.
> <URL:http://www.ietf.org/internet-drafts/draft-ietf-ftpext-mlst-15.txt>
>
> But for DIRECTORY file, as in your example, this mechanism does not
> work.  It is not easy to detect the modification of directory, i.e. if
> or not the list of meta-informations of files under a directory is
> changed after a copy was made (cached), without comparing the cached
> data and current data (which is to be transferred).
>
> Cheers,
> Yutaka

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