[Http-crcsync] http-sync standard

[Toby Collett]

Hi Alex,
Finally got a chance to read this. Is a good description of the
problem/scope.

I have a question for all with regard to RFC3229. It would be entirely
possible for us to design the http-sync to be an extension of RFC3229,
basically add a new conditional request if-blocks-match or something of the
like, and expect a response with 226 instance coding applied.

If we take this approach then our block encoding just becomes a standard
instance coding. The presence of a if-blocks-match header can be taken to
imply an accepts instance coding 'blocks' or whatever we call it to save
sending redundant information.

The question then becomes, is it worth the effort, the last lot of traffic I
saw in a quick google search on rfc3229 was in 2004 with regard to blogs and
so on. So it is not widely deployed. On the other hand with careful design
of our protocol we can be compatible, so is there a reason not to do it?

Also a minor note, rather than having a small trailing block, why dont we
just add the trailing data to the last large block, this way we dont end up
with a hash thats almost the size of the block it represents (or in some
cases bigger)

Toby

2009/4/29 Alex Wulms <alex.wulms at scarlet.be>

> Hi,
>
> Please find in attachment my current ideas on the http-crcsync protocol.
>
> I hope you don't mind but I have drafted the paper in open office and not
> as a
> plain text file. An open office version makes it easier to visibly divide
> the
> document in logical sections in order to enhance the readability and the
> structure. Though, I have added a text export for convenience, in case
> somenone might not have OO available.
>
> As I mentioned yesterday in this list, the paper is based on the insights
> that
> have grown while working on the crccache proxy modules and after studying
> the
> various papers on delta-encoding (the RFC, Toby's draft and the protocol
> proposal on the original rproxy site) and everything related to it.
>
> Like Toby proposed, maybe it would make sense to convert this into a wiki
> and
> continue the work there. What do you think?
>
> Cheers,
> Alex
>
>
>
>
>
> Op maandag 6 april 2009, schreef tridge at samba.org:
> > Hi Toby,
> >
> >  > This is transmitted in two forms. One is an SHA1 hash of the complete
> >  > chached file, and the other is a set of block hashes.
> >
> > ...
> >
> >  > Content-Hash:
> >  > This will be an sha1 hash of the entire cached body, and will allow
> the
> >  > server to transmit deltas based on its knowledge of past versions of
> the
> >  > page.
> >
> > How do you imagine that this hash would be used? I don't think it is
> > practical to think that servers would keep a record of all the dynamic
> > pages they have been served out, and for static pages I think the
> > normal cache tag mechanisms already work well.
> >
> > I think a SHA1 or similar of the servers generated page is really
> > worthwhile, but a whole file hash of what the client has in cache
> > doesn't gain anything that I can see.
> >
> > btw, I also wonder if you've seen this:
> >
> >   http://www.ietf.org/rfc/rfc3229.txt
> >
> > That is the result of earlier efforts to standardise delta encoding in
> > HTTP. I was a little bit involved in that effort, although it
> > concentrated on storing old copies on the server, which I wasn't
> > interested in.
> >
> > Still, it should provide some very useful background to the current
> > effort.
> >
> > Cheers, Tridge
> > _______________________________________________
> > Http-crcsync mailing list
> > Http-crcsync at lists.laptop.org
> > http://lists.laptop.org/listinfo/http-crcsync
>
>
>


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