Only in Bun: Astro middleware rewrite: [ERROR] Body already used

[xriter]

What version of Bun is running?

1.2.14+6a363a38d

What platform is your computer?

Darwin 24.5.0 arm64 arm

What steps can reproduce the bug?

more minimal repo

original report:

This is a continuation of this issue: withastro/astro#13844

So I tried creating the most minimal reproduction locally and I found that the issue might actually be with Bun (which I use to run astro). Somehow Bun is already consuming the request body somewhere?

// src/middleware.ts
import { sequence } from "astro/middleware";

export const onRequest = sequence((ctx, next) => {
	if (ctx.url.pathname == "/oldlink") {
		return next("/newlink");
	}
	return next();
});

// src/pages/newlink.ts
import type { APIRoute } from "astro";

export const POST: APIRoute = async ({ request }) => {
	const data = await request.json();
	return new Response(JSON.stringify(data), { status: 200 });
};

// package.json
///...
"scripts": {
    "devnode": "astro dev"
    "devbun": "bunx --bun astro dev"
}
//...

When I run this setup with Node (npm run devnode or bun run devnode), it works.
But with Bun (bun run devbun), I get [ERROR] Body already used.

What is the expected behavior?

To see the posted json.

What do you see instead?

[ERROR] Body already used

Additional information

Here is the minimal reproducible example:
https://stackblitz.com/edit/github-8mju777p-4e8ddvcl?file=src%2Fpages%2Findex.astro

[RiskyMH]

Hmm this sounds odd. I however can't manage to get any issues after cloning your stackblitz and running the bun one, I also tried to use bun in stackblitz but that didn't start bun.

Is there maybe a more complete example that I could try, or some more hints on where to look to get this.

(tried on m3 mac with latest bun)

[xriter]

@RiskyMH Sorry I think I accidentally saved some changes in my stackblitz demo while I was still trying things. I corrected it.

To reproduce follow these steps:

1. Download the stackblitz project to run it locally (I haven't figured out yet how to use Bun inside of stackblitz) (https://stackblitz.com/edit/github-8mju777p-4e8ddvcl?file=src%2Fpages%2Fnewlink.ts)
2. Assuming you have installed the latest bun version locally (right now I run 1.2.14)
3. Open the project and run bun install
4. Start the bun version of dev server with: bun run devbun
5. Use any api endpoint tool (e.g. RapidApi) and make a POST request with a random json body to localhost:4321/oldlink
6. The logs of the dev server will now show: [ERROR] Body already used

What I see when running this with Bun bun run devbun:

And what I see when I run the exact same code but with node npm run dev:

[RiskyMH]

Yay thanks for this repo, I can repo it now!

[RiskyMH]

I have made more minimal where it appears bun is consuming the request body instead of copying it:

// Minimal reproduction of bodyUsed error in Bun
function copyRequest(oldRequest: Request, newUrl: string): Request {
  if (oldRequest.bodyUsed) {
    throw new Error("bodyUsed");
  }
  return new Request(newUrl, {
    method: oldRequest.method,
    body: oldRequest.body,
    // @ts-expect-error Needed to carry over the body
    duplex: 'half',
  });
}

// Create a request with a body
const r = new Request("http://localhost:4321/oldlink", {
  method: "POST",
  body: "a",
});

// Try to copy it twice - this should fail in Bun but work in Node
console.log(copyRequest(r, "http://localhost:4321/newlink"));
console.log(copyRequest(r, "http://localhost:4321/newlink"));

This code is losely coped from https://github.com/withastro/astro/blob/de2fc9b3c406c21683b8a692fafa3cbc77ca552b/packages/astro/src/core/routing/rewrite.ts#L129-L162 which I have determined to be the cause (if i put a oldRequest = oldRequest.clone(), then it works.

Code also works in safari (jsc) & chrome & node, so is a bun issue

[xriter]

When doing rewrites in Astro, Astro indeed does some Request copying and stuff. So this Bun issue is the problem indeed.
Hopefully this can be fixed in Bun :-)

[xriter]

This minimal repro of the issue is still not fixed in Bun 1.2.20.

// Minimal reproduction of bodyUsed error in Bun
function copyRequest(oldRequest: Request, newUrl: string): Request {
  if (oldRequest.bodyUsed) {
    throw new Error("bodyUsed");
  }
  return new Request(newUrl, {
    method: oldRequest.method,
    body: oldRequest.body,
    // @ts-expect-error Needed to carry over the body
    duplex: 'half',
  });
}

// Create a request with a body
const r = new Request("http://localhost:4321/oldlink", {
  method: "POST",
  body: "a",
});

// Try to copy it twice - this should fail in Bun but work in Node
console.log(copyRequest(r, "http://localhost:4321/newlink"));
console.log(copyRequest(r, "http://localhost:4321/newlink"));