🐛 Bug Report — Runtime APIs: TransformStream with bodies is much slower than other runtimes (10-20x)

[mhart]

Researching the best way to get access to bytes in a request body, and then forward to a destination.

Some examples testing workerd with a 98MiB upload size. In this case the destination will just be the response, but you get similar results forwarding to a subrequest.

Fastest (52.8ms):

export default {
  async fetch(request) {
    return new Response(await request.arrayBuffer());
  }
}

Ok-ish (135ms):

export default {
  async fetch(request) {
    return new Response(request.body);
  }
}

Very slow (694ms):

export default {
  async fetch(request) {
    return new Response(
      request.body.pipeThrough(
        new TransformStream({
          transform(chunk, controller) {
            controller.enqueue(chunk);
          },
        }),
      ),
    );
  }
}

For comparison, the latter TransformStream pattern,

• on Bun is 33ms
• on Deno is 46ms
• on Node.js is 55ms, using this conversion:

import { createServer } from "http";
import { Readable } from "stream";

createServer(async (req, res) => {
  return Readable.fromWeb(
    Readable.toWeb(req).pipeThrough(
      new TransformStream({
        transform(chunk, controller) {
          controller.enqueue(chunk);
        },
      }),
    ),
  )
    .on("error", (err) => {})
    .pipe(res);
}).listen(8787, () => {
  console.log("Listening on http://localhost:8787");
});