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From "Tommaso Teofili (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (JCR-3534) Add JackrabbitSession.getValueByContentId method
Date Mon, 06 May 2013 07:28:16 GMT

    [ https://issues.apache.org/jira/browse/JCR-3534?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13649562#comment-13649562
] 

Tommaso Teofili commented on JCR-3534:
--------------------------------------

> the public API is still missing (BinaryReferenceMessage is in a jackrabbit internal package);
I think a public api Binary getBinaryBySecureID() (or similar) like in the first patch is
still required

I thought we weren't agreeing on this and we wanted no public APIs, but I'm open to creating
a public one.

> instead of resolving the message upon writing to the repository, it is instead written
as Binary (with the message as contents)

how would you do it instead? I understood having it as a special Binary sounded ok.

> but it's never resolved to the final binary that you want (if the message is valid)

when the binary reference message is received the receiving repository has to generate a signature
from the received content id using its own secret, if the generated signature matches the
signature received along with the content id in the reference message then it means it was
generated using the same secret and therefore comes from the same repository.
Regarding the final binary if it doesn't exist or it doesn't come from the same repository
then it has to be "sent" in a subsequent call, if it exists and the signature matches then
probably the things that's missing is if that has changed, thus probably sending something
like the actual binary length as part of the binary reference message would be helpful.

> and then you'd write the returned Binary right to the repository (no delayed resolution)

but to obtain this, wouldn't that mean that we basically send the final binary itself along
with the message?

> this is important, since the application level code needs to know if that getBinaryBySecureID()
worked or not (returns non-null or not) so it can handle the case by asking for the full binary
as stream over its own message protocol
> btw, some lucene-related java files are accidentally included in the patch with import
reorgs

thanks for pointing out, probably some overlooked left out from other changes

Alex, thanks for your comments, hopefully I've clarified what my solution looks like; if you'd
use a different approach it'd be good to have a broader overview of it (or perhaps I just
misunderstood).


                
> 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
>            Assignee: Tommaso Teofili
>         Attachments: JCR-3534.patch, 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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