Unable to proxy ReadableStream to client

[Ehesp]

Hey all,

I'm experiencing an issue streaming results from a container to a client.

I have a reproduction of the following issue with instructions: https://github.com/Ehesp/cf-containers-repro

My container (a Bun server) had an endpoint which streams back a 10 messages every second:

app.post("/stream", async (c) => {
  let remaining = 10;
  const stream = new ReadableStream({
    async start(controller) {
      while (remaining > 0) {
        console.log("enqueue:", remaining);
        controller.enqueue(
          new TextEncoder().encode(`Hello, world! ${remaining}\n\n`)
        );
        await new Promise((resolve) => setTimeout(resolve, 1000));
        remaining--;
      }

      console.log("closing stream");
      controller.close();
    },
  });

  return new Response(stream, {
    headers: {
      "Content-Type": "text/plain",
      "Transfer-Encoding": "chunked",
      "Cache-Control": "no-cache",
      "Connection": "keep-alive",
      "Content-Encoding": "identity",
    },
  });
});

Inside the DO, this is proxied via containerFetch:

  async stream() {
    const response = await this.containerFetch("http://container/stream", {
      method: "POST",
      body: JSON.stringify({
        message: "Hello, world!",
      }),
    });

    return new Response(response.body, {
      headers: response.headers,
      status: response.status,
      statusText: response.statusText,
    });
  }

My worker then proxies:

app.post("/stream", async (c) => {
  const container = getContainer(c.env.MY_CONTAINER);
  const response = await container.stream();

  return new Response(response.body, {
    headers: response.headers,
    status: response.status,
    statusText: response.statusText,
  });
});

My Node client script:

async function main() {
  const response = await fetch("http://localhost:8787/stream", {
    duplex: "half",
    method: "POST",
    body: JSON.stringify({}),
    headers: {
      "Accept-Encoding": "identity", // Tell the worker to not compress the stream
    },
  });

  console.log("client headers", Object.fromEntries(response.headers));

  for await (const chunk of response.body) {
    console.log("Client>", new TextDecoder().decode(chunk));
  }
}

main().catch((error) => {
  console.error(error);
});

I constantly get inconsistent results, either the whole thing streams (less often) or some results:

Run 1:

client headers {
  'cache-control': 'no-cache',
  'content-encoding': 'identity',
  'content-type': 'text/plain',
  date: 'Thu, 17 Jul 2025 08:54:32 GMT',
  'transfer-encoding': 'chunked'
}
Client> Hello, world! 10
Client> Hello, world! 9

Run 2:

client headers {
  'cache-control': 'no-cache',
  'content-encoding': 'identity',
  'content-type': 'text/plain',
  date: 'Thu, 17 Jul 2025 08:58:56 GMT',
  'transfer-encoding': 'chunked'
}
Client> Hello, world! 10
Client> Hello, world! 9
Client> Hello, world! 8
Client> Hello, world! 7
Client> Hello, world! 6
Client> Hello, world! 5
Client> Hello, world! 4

I'm totally unsure where the issue lies, but I've not had this issue when the origin isn't a Cloudflare Container.

[Ehesp]

Probably worth mentioning, this works perfectly fine in prod when deployed, just a local issue.

[th0m]

Hi @Ehesp thank you for the great repro steps, we will take a look.