Andy LoPresto created NIFI-5147:
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             Summary: Improve HashAttribute processor
                 Key: NIFI-5147
                 URL: https://issues.apache.org/jira/browse/NIFI-5147
             Project: Apache NiFi
          Issue Type: Improvement
          Components: Extensions
    Affects Versions: 1.6.0
            Reporter: Andy LoPresto


The {{HashAttribute}} processor currently has surprising behavior. Barring 
familiarity with the processor, a user would expect {{HashAttribute}} to 
generate a hash value over one or more attributes. Instead, the processor as it 
is implemented "groups" incoming flowfiles into groups based on regular 
expressions which match attribute values, and then generates a 
(non-configurable) MD5 hash over the concatenation of the matching attribute 
keys and values. 

In addition:
* the processor throws an error and routes to failure any incoming flowfile 
which does not have all attributes specified in the processor
* the use of MD5 is vastly deprecated
* no other hash algorithms are available

I am unaware of community use of this processor, but I do not want to break 
backward compatibility. I propose the following steps:

* Implement a new {{CalculateAttributeHash}} processor (awkward name, but this 
processor already has the desired name)
    * This processor will perform the "standard" use case -- identify an 
attribute, calculate the specified hash over the value, and write it to an 
output attribute
    * This processor will have a required property descriptor allowing a 
dropdown menu of valid hash algorithms
    * This processor will accept arbitrary dynamic properties identifying the 
attributes to be hashed as a key, and the resulting attribute name as a value
    * Example: I want to generate a SHA-512 hash on the attribute {{username}}, 
and a flowfile enters the processor with {{username}} value {{alopresto}}. I 
configure {{algorithm}} with {{SHA-512}} and add a dynamic property 
{{username}} -- {{username_SHA512}}. The resulting flowfile will have attribute 
{{username_SHA512}} with value 
{{739b4f6722fb5de20125751c7a1a358b2a7eb8f07e530e4bf18561fbff93234908aa9d2577770c876bca9ede5ba784d5ce6081dbbdfe5ddd446678f223b8d632}}
* Improve the documentation of this processor to explain the goal/expected use 
case (?)
* Link in processor documentation to new processor for standard use cases
* Remove the error alert when an incoming flowfile does not contain all 
expected attributes. I propose changing the severity to INFO and still routing 
to failure



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