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From Dave Cottlehuber <d...@muse.net.nz>
Subject Re: Introducing Bram Neijt
Date Tue, 26 Oct 2010 19:56:21 GMT
re wiki -> I will add this in next few days.

On 27 October 2010 04:39, Benjamin Young <benjamin@couchone.com> wrote:
> On 10/26/2010 11:25 AM, Adam Kocoloski wrote:
>>
>> On Oct 26, 2010, at 10:48 AM, Jan Lehnardt wrote:
>>
>>> Hi Bram,
>>>
>>> On 26 Oct 2010, at 11:51, Bram Neijt wrote:
>>>
>>>> I'm a developer at Xebia and I've been granted about 5 hours a week to
>>>> spend on implementing any open source project problem I would like to
>>>> see fixed.
>>>
>>> This major awesome! :)
>>>
>>>
>>>> I've chosen to have a go at per document authorization for couchdb.
>>>
>>> Uh-oh :) — See below.
>>>
>>>
>>>> As I'm weeding through the archives, I would love to hear about the
>>>> current approaches, who is involved, what is planned and what may be
>>>> considered an acceptable solution.
>>>
>>> To get started more generally, it might make sense to check out
>>> our list of issues sorted by how hard they are to solve:
>>>
>>>  http://s.apache.org/couchdb-easy-issues
>>>  http://s.apache.org/couchdb-medium-issues
>>>  http://s.apache.org/couchdb-hard-issues
>>>
>>> (Thanks again for Paul Davis to produce these lists)
>>>
>>> --
>>>
>>> As for per-doc auth: It is very hard to get right and probably
>>> against the nature of CouchDB. I'm not saying we shouldn't try
>>> to solve it, but we need to be aware of the impact.
>>>
>>> I remember Damien saying that Notes did get per-doc auth, but
>>> it wasn't a good solution and it sucked ever since. I don't
>>> think anybody here wants that :)
>>>
>>> The biggest problem here are views, the reduced kind.
>>>
>>>  From the reduce value, CouchDB can't deduce what documents were
>>> used to create the value.
>>>
>>> Imagine three docs
>>>
>>> {"name": "a", "amount": 3}
>>> {"name": "b", "amount": 5}
>>> {"name": "c", "amount": 7}
>>>
>>> A map function:
>>>
>>> function(doc) {
>>>  emit(doc.name, doc.amount);
>>> }
>>>
>>> A reduce function:
>>>
>>> function(keys, values) {
>>>  return sum(values);
>>> }
>>>
>>> Now the reduced result for this view is 15. Now say you don't
>>> have access to read the document with `"name": "b"`. Should you
>>> be able to access the view? If yes, what result should you see?
>>> 15? 10?
>>>
>>> If you get 15, then the view is leaking information that you
>>> are not supposed to see (IIRC that's how Notes works).
>>>
>>> If you are supposed to get 10, the underlying data structure
>>> would have to compute a view for each user based on his/her
>>> authorization settings. And invalidate the view every time
>>> these are changed.
>>>
>>> To make a rather straightforward implementation of that, J Chris
>>> proposed the idea of prefixing views with the username and only
>>> allowing reads with a prefix that is the authenticated username.
>>>
>>> While that is conceptually rather easy, you are basically creating
>>> a view for each user. This may work for small amounts of data,
>>> but not large, and many users.
>>>
>>>
>>> Again, I'm not saying, you shouldn't attempt to solve this,
>>> because that'd be über-rad, but there be dragons :)
>>>
>>> Either way, you may want to jump in with the easier open issues
>>> to get a feeling for the codebase and the procedure of submitting
>>> patches and all that.
>>>
>>> Glad to have you on board!
>>>
>>> Cheers
>>> Jan
>>> --
>>
>> Well said Jan, and welcome Bram!  This explanation needs to not get lost
>> in the archives.
>
> +1 for getting this on the wiki, a blog, or somewhere that it's findable.
> It's sort of become "lore" that per-document permissions aren't currently
> doable in CouchDB, but this is the clearest explanation I've heard, and
> worth repeating in a more public venue. :)
>
> Thanks, Jan,
> Benjamin
>>
>> Adam
>>
>
>

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