Chunked Transfer Encoding for Dynamic Response Streams

A server generating a large or infinite response cannot set Content-Length upfront, causing the client to wait for the full response or the connection to close unexpectedly.

Use chunked transfer encoding: HTTP/1.1 allows sending Transfer-Encoding: chunked without a Content-Length. Each chunk is prefixed with its size in hex.

In Node.js, res.write() automatically enables chunked encoding when res.end() hasn't been called.

app.get('/stream', async (req, res) => {
  res.setHeader('Content-Type', 'application/json');
  // Do NOT call res.json() or res.send() — use write/end
  res.write('[');
  let first = true;
  for await (const item of generateItems()) {
    if (!first) res.write(',');
    res.write(JSON.stringify(item));
    first = false;
  }
  res.write(']');
  res.end();
});

Without chunked encoding, the server must buffer the entire response to calculate Content-Length, defeating streaming. Chunked encoding signals the end of each chunk, and a zero-length chunk signals end of the response.