Transform Streams

Transform Streams
- Encrypt Some Data
- Transform stdin to uppercase text

Transform streams, in practice: take input from a stream, transform the data (up to us as developers WHAT how they transform), and "pass" the data along to another stream.

A createTransformStream functioin can be built. This funciton could

return a Transform object (stream)
contain the "logic" of the transformation

Encrypt Some Data

Here, an example of a transform stream that encrypts the data passed to it:

const { Transform } = require('stream')
const { scrypt } = require('crypto')
const ENCRYPTION_SALT = 'salt-here';

// build the transform stream creator
const createTransformStream = () => {
  return new Transform({
    decodeStrings: false,
    encoding: 'hex',
    transform (chunk, enc, next) {
      scrypt(chunk, ENCRYPTION_SALT, 32, (err, key) => {
        if (err) {
          next(err);
          return;
        }
        next(null, key);
      });
    }
  })
}
const transform = createTransformStream()

// register a listener for the transform stream instance
transform.on('data', (data) => {
  console.log('got data:', data)
})

// send some data to the transform stream
transform.write('First line\n')
transform.write('Second line\n')
transform.write('Third Line\n')
transform.end('Last line')

Running that will return:

got data: e0046ff16bca85fcc79483d59ff01a8cd0dbdf206ea2aec29b8e38af396e52da
got data: 063e61c30148f5d2649c7e1db30de10bb697a4be41d643d62c3c4284a2681890
got data: 167fe3aa6c27c68fc133b18ced4ed98f94a51ebcd0d087ed66498614fa33c066
got data: 6b6b3ea91b7c0b88ce682745f73d51ef266e60a7fc06b85072338e85c3bd808d

Transform stdin to uppercase text

This example combines a createTransformStream function with piping and stdio:

// to-upper.js

const { Transform } = require('stream');

function createUppercaseStream(){
  return new Transform({
    transform(chunk,encoding,next){
      const upd = chunk.toString().toUpperCase()
      next(null,upd)
    }
  })
}

const upperStream = createUppercaseStream()
process.stdin.pipe(upperStream).pipe(process.stdout)

Running that with something like node to-upper.js will keep the terminal open. once the terminal is open, writing something in the terminal like this is some text will cause the process.stdin to get piped to the upperStream. The upperStream takes the input and runs .toString().toUpperCase() on it. Then, the output of THAT command getss piped to process.stdout which is the same terminal that the text was entered in. The terminal should immediately output THIS IS SOME TEXT.

Tags:

node

streams

core

transformation