Chunked encoding is broken after using this middleware

Question

Chunked encoding is broken after using this middleware

Sw0rdstream opened this issue 4 years ago · 1 comments

Demo to reproduce the problem:

const express = require('express')
const compression = require('compression');
const app = express()
const port = 3001

// after using compression, the first chunk will not be sent until the second chunk is written.
app.use(compression());
app.get('/', (req, res) => {
  res.statusCode = 200;
  res.setHeader('Content-Type', 'text/html');
  res.setHeader('Transfer-Encoding', 'chunked');
  res.write('<html><body>First chunk <br>');
  process.nextTick(function (){
    // simulate a long wait in order to confirm chunk encoding in browser easily
    for(var i = 0; i<4000000000; i++){}
    res.write('Second chunk </body></html>');
    res.end();
  });
})

app.listen(port, () => {
  console.log(`Example app listening at http://localhost:${port}`)
})

Once removing the code of using compression(), the chunked encoding will work well.

Answer 1 · 2021-07-07T16:11:27.000Z

Yes, that is expected due to how compression works. The compression algorithm will wait for enough data to compress a full chunk. This module provides the res.flush() method in order to signal that you want the compression algorithm to prematurely get flushed, resulting in a diminished compression ratio.