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From "Jukka Zitting (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (JCR-3534) Add JackrabbitSession.getValueByContentId method
Date Thu, 21 Mar 2013 14:33:17 GMT

    [ https://issues.apache.org/jira/browse/JCR-3534?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13608985#comment-13608985
] 

Jukka Zitting commented on JCR-3534:
------------------------------------

Note that there is no guarantee that the userIds of the two repositories have no relation
with each other, so I don't think it should be included in a mechanism like the one proposed.

Instead, a HMAC of the content identifier, signed by the underlying data store should be good
enough. The target repository can check that the message comes from the same underlying data
store, so anyone who has access to such a code already has access to the related binary through
one of the repositories attached to that data store. Thus allowing the user to access the
binary doesn't reveal anything he or she couldn't already access by other means.

Ideally I'd see such a HMAC to be passed transparently as a part of Binary instances acquired
from a remote RMI or Davex connection to the source repository. The target repository would
automatically extract and evaluate the information based on the type of the passed Binary
instance, and could always fall back to streaming the data if for example the HMAC doesn't
match. The client would use the pattern I outlined above, the only difference being that repositoryA
would be a remote RMI or Davex connection instead of a local cluster node.
                
> Add JackrabbitSession.getValueByContentId method
> ------------------------------------------------
>
>                 Key: JCR-3534
>                 URL: https://issues.apache.org/jira/browse/JCR-3534
>             Project: Jackrabbit Content Repository
>          Issue Type: New Feature
>          Components: jackrabbit-api, jackrabbit-core
>    Affects Versions: 2.6
>            Reporter: Felix Meschberger
>         Attachments: JCR-3534.patch
>
>
> we have a couple of use cases, where we would like to leverage the global data store
to prevent sending around and copying around large binary data unnecessarily: We have two
separate Jackrabbit instances configured to use the same DataStore (for the sake of this discussion
assume we have the problems of concurrent access and garbage collection under control). When
sending content from one instance to the other instance we don't want to send potentially
large binary data (e.g. video files) if not needed.
> The idea is for the sender to just send the content identity from JackrabbitValue.getContentIdentity().
The receiver would then check whether the such content already exists and would reuse if so:
> String ci = contentIdentity_from_sender;
> try {
>     Value v = session.getValueByContentIdentity(ci);
>     Property p = targetNode.setProperty(propName, v);
> } catch (ItemNotFoundException ie) {
>     // unknown or invalid content Identity
> } catch (RepositoryException re) {
>     // some other exception
> }
> Thus the proposed JackrabbitSession.getValueByContentIdentity(String) method would allow
for round tripping the JackrabbitValue.getContentIdentity() preventing superfluous binary
data copying and moving. 
> See also the dev@ thread http://jackrabbit.markmail.org/thread/gedk5jsrp6offkhi

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