[jira] [Created] (NIFI-12386) Add a FilterAttributes processor

["endzeit (Jira)" <ji...@apache.org>]

endzeit created NIFI-12386:
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             Summary: Add a FilterAttributes processor
                 Key: NIFI-12386
                 URL: https://issues.apache.org/jira/browse/NIFI-12386
             Project: Apache NiFi
          Issue Type: New Feature
          Components: Core Framework
            Reporter: endzeit
            Assignee: endzeit


Flows in Apache NiFi can get quite sophisticated, consisting of a long chains of both {{ProcessGroup}} and {{Processor}} components.
Oftentimes {{Processor}} components, including those in the NiFi standard bundle, enrich an incoming {{FlowFile}} with additional FlowFile attributes.
This can lead to a fair amount of different FlowFile attributes accumulating over the FlowFile's lifecycle.

In order to prevent subsequent {{ProcessGroup}} / {{Processor}} components to accidentally rely on implementation details of preceding components, a good practice is to:
 # define which FlowFile attributes should exist at selected points in the {{Flow}}
 # reduce the attributes of the FlowFile at the selected point to those defined

This can be achieved by using the [UpdateAttribute|https://nifi.apache.org/docs/nifi-docs/components/org.apache.nifi/nifi-update-attribute-nar/1.23.2/org.apache.nifi.processors.attributes.UpdateAttribute/index.html] processor of the standard processor bundle.

However, the {{UpdateAttribute}} processor allows only for a regular expression to define a set of attributes to remove. Instead, the outlined practice above desires to explicitly state a set of attributes to keep. One can do so with a regular expression as well, but writing the reverse lookup to achieve this is not the easiest endeavor to put it mildly.

This issue proposes a new processor {{FilterAttributes}} to be added to the library of {{{}nifi-standard-processors{}}}, which can be configured with a set of attributes and removes all attributes of an incoming FlowFile other than the ones configured.

The processor should
 * have a required, non-blank property "Attributes to keep", which takes a list of attribute names separated by delimiter, e.g. comma (,).
 ** trailing whitespace around attribute names should be ignored
 ** leading or trailing delimiters should be ignored
 * have a required, non-blank property "Delimiter", which is used to delimit the individual attribute names, with a default value of "," (comma).
 * have a single relationship "success" to which all FlowFiles are routed, similar to {{UpdateAttribute}}
 * have an [InputRequirement|https://www.javadoc.io/doc/org.apache.nifi/nifi-api/latest/org/apache/nifi/annotation/behavior/InputRequirement.html] of [INPUT_REQUIRED|https://www.javadoc.io/doc/org.apache.nifi/nifi-api/latest/org/apache/nifi/annotation/behavior/InputRequirement.Requirement.html]
 * [@SupportsBatching|https://www.javadoc.io/doc/org.apache.nifi/nifi-api/latest/org/apache/nifi/annotation/behavior/SupportsBatching.html]
 * be [@SideEffectFree|https://www.javadoc.io/doc/org.apache.nifi/nifi-api/latest/org/apache/nifi/annotation/behavior/SideEffectFree.html]

Some possible extension might be:
 * have a required property "Core attributes", with allowable values of "Keep UUID only", "Keep all", with a default of "Keep UUID only"
 ** an additional allowable value e.g. "Specify behaviour" may be added, which allows for more customization



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