NIFI-4184: PutHDFS Processor Expression language TRUE on REMOTE_GROUP & REMOTE_OWNER

[panelladavide]

I needed to put some attributes on REMOTE_GROUP and REMOTE_OWNER, in order to achieve it i put expressionLanguageSupported(true) on the PropertyDescriptor of REMOTE_GROUP and REMOTE_OWNER

Signed-off-by: Davide davidde85@hotmail.it

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[ijokarumawak]

Hi @panelladavide thanks for your contribution!

In order to enable Expression Language, setting expressionLanguageSupported to true is not enough. You also need to evaluate the configured EL. Plus, if you need to support EL to use FlowFile attribute, you need to pass a FlowFile (the incoming FlowFile in most cases) when EL is evaluated.

Specifically, you need to modify changeOwner method:

• Add EL evaluation like:

  String owner = context.getProperty(REMOTE_OWNER).evaluateAttributeExpressions(flowFile).getValue();
  

• Add FlowFile argument, so that it can be passed to evaluateAttributeExpressions(flowFile)

https://github.com/apache/nifi/blob/master/nifi-nar-bundles/nifi-hadoop-bundle/nifi-hdfs-processors/src/main/java/org/apache/nifi/processors/hadoop/PutHDFS.java#L389

[panelladavide]

@ijokarumawak Thank you so much!
As soon as I have time to code I will update my branch.

I have a question. Why did not you enable the EL in PutHDFS REMOTE_OWNER and GROUP_OWNER?
Is there a specific reason?

[ijokarumawak]

@panelladavide I don't know any reason for not supporting EL with REMOTE_OWNER/GROUP. I think applying EL at incoming FlowFile level is safe, and wouldn't break anything because it just sets owner for a specific path.

It would be problematic if it changes FileSystem or HdfsResources instance state those are reused from every onTrigger call. But again, setting owner should just affect the specified path, so it should be fine.

I guess it's just written that way at the initial contribution and haven't been requested until now.

[panelladavide]

Thank you so much!

[ijokarumawak]

@panelladavide Thanks for the updates! I tested with my Hadoop cluster, basically it works as expected, but I found minor issue with EL returning an empty string. Please update it once again, and it will be ready to be merged. Thanks a lot!

[ijokarumawak]

Trivial, please add a whitespace between arguments.

[ijokarumawak]

Please remove these old lines. We don't have to keep old code unless if there's a strong needs.

[ijokarumawak]

When I tested with an expression that returns no value, e.g. specify an attribute name which does not exist, then the group string became an Empty string. And the file was updated with an empty group. To avoid that, Could you add following code before this if statement? to make empty string into null:

            owner = owner == null || owner.isEmpty() ? null : owner;
            group = group == null || group.isEmpty() ? null : group;

[ijokarumawak]

@panelladavide LGTM, +1. I'm going to merge. Thanks for your contribution!

[panelladavide]

Thanks for your help and for your patience! Why AppVeyor build failed? When Nifi release a new release?

[ijokarumawak]

AppVeyor build has been failing. There are many unit tests those are not working well on Windows. We've been trying to improve it but not completed.