Python ExecuteScript in NiFi: Transform flowfile attributes & content

Question

I am trying to create a Python script in NiFi that:

1. Reads some attributes from an incoming flowfile
2. Read the json content of the flowfile & extract specific fields
3. Write attributes to outgoing flowfile
4. Overwrite incoming flowfile with new content that is created in the script (e.g. API call that returns new json) and send it to SUCCESS relationship OR remove the old flowfile and create new with desired content

What i ve done so far:

import json
import java.io
from org.apache.commons.io import IOUtils
from java.nio.charset import StandardCharsets
from org.apache.nifi.processor.io import StreamCallback,InputStreamCallback, OutputStreamCallback

class OutputWrite(OutputStreamCallback, obj):

def __init__(self):
    self.obj = obj

def process(self, outputStream):

    outputStream.write(bytearray(json.dumps(self.obj).encode('utf')))

###end class###

flowfile = session.get()

if flowfile != None:

**#1) Get flowfile attributes**

    headers = {
        'Accept-Encoding': 'gzip, deflate, br',
        'Accept': 'application/json, text/plain, */*',
        'Cache-Control': 'no-cache',
        'Ocp-Apim-Trace': 'true',
        'Authorization': flowfile.getAttribute('Authorization')
    }

    collection = flowfile.getAttribute('collection')
    dataset = flowfile.getAttribute('dataset')

    **#2)Get flowfile content**

    stream_content = session.read(flowfile)
    text_content = IOUtils.toString(stream_content, StandardCharsets.UTF_8)
    json_content = json.loads(text_content)

    records = json_content['result']['count']
    pages = records/10000

    **#3) Write flowfile attributes**

    flowfile = session.putAttribute(flowfile, 'collection', collection)
    flowfile = session.putAttribute(flowfile, 'dataset', dataset)

    **#API operations: output_json with desired data**

    output_json = {some data}

    **#4) Write final JSON data to output flowfile**

    flowfile = session.write(flowfile, OutputWrite(output_json))

    session.transfer(flowfile, REL_SUCCESS)
    session.commit()

My problem is that i can't find a way to pass a reference to the desired output_json object as an argument in the OutputStreamCallback class. Any ideas on how to resolve this or maybe a better approach?

Is it maybe easier to perform all API operations in this case within the process function of the class, but then how do i get access to the incoming flowfile attributes within the process function (requires a session or a flowfile object) ?

Any help much appreciated!

Answer 1

You can try something like this-

import json
import sys
import traceback
from java.nio.charset import StandardCharsets
from org.apache.commons.io import IOUtils
from org.apache.nifi.processor.io import StreamCallback
from org.python.core.util import StringUtil

class TransformCallback(StreamCallback):
    def __init__(self):
        pass

    def process(self, inputStream, outputStream):
        try:
            # Read input FlowFile content
            input_text = IOUtils.toString(inputStream, StandardCharsets.UTF_8)
            input_obj = json.loads(input_text)
            # Transform content
            output_obj = input_obj   #your input content

            #perform Data tranformation on output_obj

            # Write output content
            output_text = json.dumps(outputJson)
            outputStream.write(StringUtil.toBytes(output_text))
        except:
            traceback.print_exc(file=sys.stdout)
            raise


flowFile = session.get()
if flowFile != None:
    flowFile = session.write(flowFile, TransformCallback())

    # Finish by transferring the FlowFile to an output relationship
    session.transfer(flowFile, REL_SUCCESS)