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From "Mclean, Adam" <adam.mcl...@rbc.com>
Subject RE: Storing text/plain attachments and digest
Date Fri, 02 Nov 2012 02:09:14 GMT
Of course! Makes perfect sense considering the compression.  Adding my
own property to the document sounds like the winner then.

Thanks for the direction.

-----Original Message-----
From: Robert Newson [mailto:rnewson@apache.org] 
Sent: 2012, November, 01 8:18 PM
To: user@couchdb.apache.org
Subject: Re: Storing text/plain attachments and digest

To be specific, the Content-MD5 is always the MD5 of the response body,
but this is not necessarily true for ETag. If you do want it to match,
then either use a content-type that is not going to be compressed, or
remove the content-type from couchdb's configuration.

It is appropriate (w.r.t RFC 2616) to depend on the Content-MD5 header.
If you supply when when PUT'ting a standalone attachment, we'll even
verify it matches and return an error if it doesn't.

Jens, I'm not familiar with that optimization but, if it exists, it came
after I exposed the MD5 in this manner. The only place I think the
replicator is involved is that, by emitting this information, the
replicator validates that attachments aren't corrupted in transit.


On 2 November 2012 00:05, Jens Alfke <jens@couchbase.com> wrote:

>
> On Nov 1, 2012, at 1:49 PM, "Mclean, Adam" <adam.mclean@rbc.com>
wrote:
>
> > The digest produced by the file upload is key to this working for me

> > so I'm not replacing files that are already the same in couch.  I've

> > been
>
> IMHO you should not try to interpret the contents of the attachment 
> 'digest' property. It's mostly meant as an optimization for the 
> replicator, not as a user feature. Don't assume that it consists of 
> the string "md5-" followed by a hex MD5 digest of the actual 
> attachment contents. As you've seen, this isn't true for compressed 
> attachments. It's even more untrue for attachments on TouchDB, which
uses a SHA1 digest instead.
>
> If you need to track the identities of attachments using a digest, it 
> would be safer to add your own digest property to the document, so 
> that you have control over how it's generated.
>
> -Jens
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