Communication node<>python via JSON

main.js

process.env.PYTHONUNBUFFERED = '1'

const spawn = require('child_process').spawn
const path = require('path')

var pythonExec = function(algo_file, params, cb) {
  var init_data = params.init_data
  var receivedData = params.receivedData
  var dataString = ''

  var py = spawn('python3', ['-u', algo_file], {
    env: process.env,
    shell : true
  })

  py.on('error', (error) => {
    cb(error)
  })

  py.stderr.on('data', (data) => {
    console.error(`[ERR] ${data}`)
  })

  py.stdout.on('data', function(data){
    if (data == 'ready\n') {
      py.stdin.write(JSON.stringify(init_data))
      py.stdin.write('\n');
      return
    }

    data = data.toString()
    receivedData(data)
  })

  py.stdout.on('end', function(){
    py.stdin.end()
    cb(null, dataString)
  })

}

if (require.main === module) {

  var init_data = {
    "params": {
      "percent": 0.9,
      "kernel": 2
    }
  }

  pythonExec('./worker.py', {
    init_data: init_data,
    receivedData: (data) => {
      console.log('Received Data cb')
      console.log(data)
    }
  }, (err, res) => {
    console.log('Script ended')
    console.log(`Error = ${err}`)
  })
}

worker.py

import cv2
import numpy as np

import time
from detector import MotionDetector
from packer import pack_images

import json
import os
import sys
import numpy as np

def read_in_v2():
    k = 0
    try:
        buff = ''
        while True:
            buff += sys.stdin.read(1)
            if buff.endswith('\n'):
                return json.loads(buff[:-1])
                buff = ''
                k = k + 1
    except KeyboardInterrupt:
        sys.stdout.flush()
        pass
    return json.loads(lines[0])

def processing():
    print('ready')
    obj = read_in_v2()
    print(json.dumps(obj))
    time.sleep(4)
    print(json.dumps(obj))

if __name__ == "__main__":
    processing()