NodeJS sample for copying files using streams with backpressure.

backpressure-stream.js

const { createReadStream, createWriteStream} = require('fs');

// You should include a real file live video, image, etc
const readStream = createReadStream(__dirname+'/powder-day.mp4');
const writeStream = createWriteStream(__dirname+'/copy.mp4', { highWaterMark: 1628920 });

// => flowing stream
readStream.on('data', (chunk) => {
    // if this will be false, meaning the stream is full
    const result = writeStream.write(chunk);
    // pause the flow temporarily
    if (!result) {
        console.log('backpressure');
        readStream.pause();
    }
});

readStream.on('end', () => {
    writeStream.end();
});

readStream.on('error', (err) => {
    console.log(`====> ${err}`);
});

// if the stream is ready or empty, pour some stream again
// note this is on writeStream, not on readStream
writeStream.on('drain', () => {
    console.log('drained');
    readStream.resume();
});

writeStream.on('close', () => {
    process.stdout.write('file copied');
});