Streams: backpressure

gistfile1.txt

import { blue, bold, cyan, green, yellow } from 'kleur';
import { clear, log } from 'node:console';
import { createReadStream } from 'node:fs';
import { join } from 'node:path';
import { PassThrough, Readable } from 'node:stream';

clear();

// const path = join(__dirname, '../files/13KB.pdf');
// const path = join(__dirname, '../files/1MB.pdf');
const path = join(__dirname, '../files/1.5MB.pdf');

const stream = createReadStream(path);
const passThrough = new PassThrough({ highWaterMark: 1024 });

listenToEvents('stream', stream);
listenToEvents('passThrough', passThrough);

stream.pipe(passThrough);

// - Comment this to create backpressure and pause the stream as soon as the PassThrough's internal "bucket" fills up.
// - Uncomment this to drain the "bucket" and keep the stream flowing.
// passThrough.on('data', (chunk: Uint8Array) => {
//   log(
//     `${blue('i')} ${bold('passThrough')}: data received (length: ${
//       chunk.length
//     })`
//   );
// });

function listenToEvents(name: string, stream: Readable) {
  stream
    .on('pause', () => log(`${yellow('‼')} ${bold(cyan(name))}: paused`))
    .on('resume', () => log(`${blue('i')} ${bold(cyan(name))}: resumed`))
    .on('drain', () => log(`${blue('i')} ${bold(yellow(name))}: drained`))
    .on('end', () => log(`${green('✔')} ${bold(green(name))}: ended`));
}

gistfile2.txt

{
  "name": "streams",
  "version": "1.0.0",
  "description": "",
  "main": "index.js",
  "scripts": {
    "start": "nodemon ./src/index.ts"
  },
  "keywords": [],
  "author": "",
  "license": "ISC",
  "devDependencies": {
    "@types/node": "^20.10.6",
    "nodemon": "^3.0.2",
    "ts-node": "^10.9.2",
    "typescript": "^5.3.3"
  },
  "dependencies": {
    "kleur": "^4.1.5"
  }
}

gistfile3.txt

{
  "compilerOptions": {
    "target": "es2022",
    "module": "commonjs",
    "esModuleInterop": true,
    "forceConsistentCasingInFileNames": true,
    "strict": true,
    "skipLibCheck": true
  }
}