smartstream/test/backpressure.ts

import { SmartDuplex, type ISmartDuplexOptions, StreamWrapper } from '../ts/index.js';

import * as smartdelay from '@push.rocks/smartdelay';

async function testBackpressure() {
  const stream1 = new SmartDuplex({
    objectMode: true,
    handleBackpressure: true,
    writeFunction: async (chunk, tools) => {
      console.log(`processed chunk ${chunk} in stream 1`);
      return chunk; // Fast processing
    }
  });
  const stream2 = new SmartDuplex({
    objectMode: true,
    handleBackpressure: true,
    writeFunction: async (chunk, tools) => {
      await new Promise(resolve => setTimeout(resolve, 100)); // Slow processing
      console.log(`processed chunk ${chunk} in stream 2`);
      return chunk;
    }
  }); // This stream processes data more slowly
  const stream3 = new SmartDuplex({
    handleBackpressure: false,
    writeFunction: async (chunk, tools) => {
      console.log(`finished chunk ${chunk} in stream 3`);
    }
  });

  stream1.pipe(stream2).pipe(stream3);

  let backpressured = false;
  for (let i = 1; i < 100; i++) {
    const canContinue = stream1.write(`Chunk ${i}`, 'utf8');
    if (!canContinue) {
      backpressured = true;
      console.log(`Backpressure at chunk ${i}`);
    }
  }

  stream1.end();

  stream1.on('finish', () => {
    console.log('Stream 1 finished processing.');
  });
  stream2.on('finish', () => {
    console.log('Stream 2 finished processing.');
  });
  stream3.on('finish', () => {
    console.log('Stream 3 finished processing.');
    if (!backpressured) {
      console.log('No backpressure was observed.');
    }
  });
}

testBackpressure();