Res Write Pipe Interleave

Stage 2: a raw res.write and req.pipe(res) on ONE response share a single per-response output queue, so their bytes leave the socket in call order. The handler writes a prefix directly with res.write, then pipes the request body straight back; the client sees the prefix before the echoed body. (Both paths used to have independent output paths that could interleave out of order.)

import http from 'http';
import type { AddressInfo } from 'net';

async function consume(port: number): Promise<void> {
  const res = await fetch("http://127.0.0.1:" + port + "/", {
    method: "POST",
    body: "the quick brown fox",
  });
  const text = await res.text();
  console.log("body:", text);
  console.log("ordered:", text === "PREFIX:the quick brown fox");
  process.exit(0);
}

const server = http.createServer((req: http.IncomingMessage, res: http.ServerResponse) => {
  res.writeHead(200, { "Content-Type": "application/octet-stream" });
  res.write("PREFIX:");
  req.pipe(res);
});

server.listen(0, () => {
  const port: number = (server.address() as AddressInfo).port;
  console.log("listening:", port > 0);
  setTimeout(() => { consume(port); }, 50);
});

View source on GitHubexamples/http/res_write_pipe_interleave.ts

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