🐛 BUG: miniflare.dispatchFetch() buffers streaming responses

[wilsonpage]

Which Cloudflare product(s) does this pertain to?

Miniflare

What versions are you using?

3.20241230.0[miniflare]

What operating system and version are you using?

OSX 15.2

Please provide a link to a minimal reproduction

No response

Describe the Bug

I'm using miniflare in test to assert my app is delivering the expected chunks in a streamed response. When I run the miniflare server locally and hit the endpoint using curl I get the expected chunks delivered as soon as they are enqueued. When I use miniflare.dispatchFetch() the chunks are all delivered at once when the stream is closed, suggesting that .dispatchFetch is somehow buffering the response internally?

Worker server code:

export const routeHandler = (request, env) => {
 const stream = new ReadableStream({
    async start(controller) {
      const encoder = new TextEncoder();
      let i = 0;

      while (i++ < 3) {
        controller.enqueue(encoder.encode(`${i}\n`));
        console.log('enqueue', i);
        await wait(1000);
      }

      controller.close();
    }
  });

  const response = new Response(stream, {
    headers: {
      'content-type': 'text/plain',
      'transfer-encoding': 'chunked',
    },
  });

  return response;
};

Client code

  const res = await miniflare.dispatchFetch(
    new URL('/cache/url/stream', 'http://localhost:4000/').toString(),
    {
      method: 'GET',
    }
  );

  if (!res.body || !(res.body instanceof ReadableStream)) {
    throw new Error('expected stream');
  }

  console.log('got status', res.status);

  const reader = res.body.getReader();
  const decoder = new TextDecoder();

  while (true) {
    const { value, done } = await reader.read();
    console.log(decoder.decode(value));

    if (done) {
      break;
    }
  }

Log output

[mf:inf] Ready on http://127.0.0.1:4000
enqueue 1
got status 200
[mf:inf] GET /cache/url/stream 200 OK (13ms)
enqueue 2
enqueue 3
1
2
3

Note how the client logs all happen after the final chunk is enqueued and the stream is closed.

Please provide any relevant error logs

No response