Basic writable stream backpressure example

writableBackpressure.js

const Chance = require('chance');
const http = require('http');
const chance = new Chance();

http.createServer((req, res) => {
  res.writeHead(200, { 'Content-Type': 'text/plain' });
  
  const generateMore = () => {
    while(chance.bool({ likelihood: 95 })) {
      let shouldContinue = res.write(
        chance.string({ length: (16 * 1024) - 1 })
      );

      if(!shouldContinue) {                          // [1]
        console.log('backpressure');
        return res.once('drain', generateMore);
      }
    }

    res.end('\n The end... \n', () => {              // [2]
      console.log('All data was sent')
    })
  }

  generateMore();
})
  .listen(3000, () => {
    console.log('Listening on port 3000');
  })


// [1] Triggers when internal buffer is full. Return statement stops out
//     of function and registers a one-time 'drain' listener, which
//     waits for buffer to be flushed before invoking generateMore()
//
// [2] Signal end of write stream when while condition fails