Hi Team,
For OAK-1963 we need to allow access to actaul Blob location say in form
File instance or S3 object id etc. This access is need to perform optimized
IO operation around binary object e.g.
1. The File object can be used to spool the file content with zero copy
using NIO by accessing the File Channel directly [1]
2. Client code can efficiently replicate a binary stored in S3 by having
direct access to S3 object using copy operation
To allow such access we would need a new API in the form of
AdaptableBinary.
API
===
public interface AdaptableBinary {
/**
* Adapts the binary to another type like File, URL etc
*
* @param <AdapterType> The generic type to which this binary is adapted
* to
* @param type The Class object of the target type, such as
* <code>File.class</code>
* @return The adapter target or <code>null</code> if the binary cannot
* adapt to the requested type
*/
<AdapterType> AdapterType adaptTo(Class<AdapterType> type);
}
Usage
=====
Binary binProp = node.getProperty("jcr:data").getBinary();
//Check if Binary is of type AdaptableBinary
if (binProp instanceof AdaptableBinary){
AdaptableBinary adaptableBinary = (AdaptableBinary) binProp;
//Adapt it to File instance
File file = adaptableBinary.adaptTo(File.class);
}
The Binary instance returned by Oak
i.e. org.apache.jackrabbit.oak.plugins.value.BinaryImpl would then
implement this interface and calling code can then check the type and cast
it and then adapt it
Key Points
========
1. Depending on backing BlobStore the binary can be adapted to various
types. For FileDataStore it can be adapted to File. For S3DataStore it can
either be adapted to URL or some S3DataStore specific type.
2. Security - Thomas suggested that for better security the ability to
adapt should be restricted based on session permissions. So if the user has
required permission then only adaptation would work otherwise null would be
returned.
3. Adaptation proposal is based on Sling Adaptable [2]
4. This API is for now exposed only at JCR level. Not sure should we do it
at Oak level as Blob instance are currently not bound to any session. So
proposal is to place this in 'org.apache.jackrabbit.oak.api' package
Kindly provide your feedback! Also any suggestion/guidance around how the
access control be implemented
Chetan Mehrotra
[1] http://www.ibm.com/developerworks/library/j-zerocopy/
[2]
https://sling.apache.org/apidocs/sling5/org/apache/sling/api/adapter/Adaptable.html
