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From "Alexander Klimetschek (JIRA)" <j...@apache.org>
Subject [jira] [Comment Edited] (JCR-3534) Efficient copying of binaries across repositories with the same data store
Date Mon, 06 May 2013 10:56:16 GMT

    [ https://issues.apache.org/jira/browse/JCR-3534?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13649645#comment-13649645
] 

Alexander Klimetschek edited comment on JCR-3534 at 5/6/13 10:55 AM:
---------------------------------------------------------------------

@Tommaso: In the current patch, the binary stores the HMAC message/reference, but not the
real binary. This it not transparent for JCR API users. How do they get the actual binary?
They don't have access to the DataStore at all, and they should not have to know about this
special mechanism at all (otherwise all code would have to be rewritten).

What I think we need on the API client side:
a) creating binary

Node node = ... // current node written
Binary binary;
if (messageData.hasBinaryStream()) {
    binary = getBinaryFromStream(messageData, session);
} else {
    String message = messageData.getBinaryMessage(); // get from custom protocol
    binary = jackrabbitSession.getBinaryBySecureID(message);
    if (binary == null) {
        // protocol does an extra step and transfers the full binary itself
        return ASK_FOR_BINARY_STREAM;
    }
}
node.setProperty("jcr:data", binary);


b) code reading the data - plain jcr api

InputStream is = node.getProperty("jcr:data").getBinary().getInputStream();
                
      was (Author: alexander.klimetschek):
    [~teofili] In the current patch, the binary stores the HMAC message, but not the real
binary. This it not transparent for JCR API users. How do they get the actual binary? They
don't have access to the DataStore at all, and they should not have to know about this special
mechanism at all (otherwise all code would have to be rewritten).

What I think we need on the API client side:
a) creating binary

Node node = ... // current node written
Binary binary;
if (messageData.hasBinaryStream()) {
    binary = getBinaryFromStream(messageData, session);
} else {
    String message = messageData.getBinaryMessage(); // get from custom protocol
    binary = jackrabbitSession.getBinaryBySecureID(message);
    if (binary == null) {
        // protocol does an extra step and transfers the full binary itself
        return ASK_FOR_BINARY_STREAM;
    }
}
node.setProperty("jcr:data", binary);


b) code reading the data - plain jcr api

InputStream is = node.getProperty("jcr:data").getBinary().getInputStream();
                  
> Efficient copying of binaries across repositories with the same data store
> --------------------------------------------------------------------------
>
>                 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-3534.2.patch, 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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