Question about streams - "This ReadableStream is disturbed"

[vicb]

ref issue: #2746

^ this issue is about workerd streams not compatible with Node stream. The reason is that we want to stick to the specs while Node (/undici) does not.

In workerd, it is not possible to initialize the body with a Readable as in:

const req = new Request('http://example.com', { method: 'POST', body: readable });

We have used a workaround for NextJS: { body: Readable.toWeb(readable) }

The workaround stopped working following some updates in the Next adapter code base.

There is a repro in https://github.com/vicb/workerd-stream

• checkout the code
• npm i
• npx wrangler dev
• hit b in the console to send a request (or use curl)

You will see the following error:

[wrangler:err] TypeError: This ReadableStream is disturbed (has already been read from), and cannot be used as a body.
    at Object.fetch (file:///Users/vberchet/code/work/extends-readable/src/index.ts:80:15)
    at fetchDispatcher (file:///Users/vberchet/code/work/extends-readable/.wrangler/tmp/bundle-IHVd6O/middleware-loader.entry.ts:54:17)

It originates in:

// Error with:
// TypeError: This ReadableStream is disturbed (has already been read from), and cannot be used as a body.
const req = new Request('http://example.com', { method: 'POST', body: Readable.toWeb(ic) });

// Works
//const req = new Request('http://example.com', { method: 'POST', body: ReadableStream.from(ic) });

You can see that the first snippet that used to work now error.

ic is an instance of IncomingMessage (local) < http.IncomingMessage (unenv) < Readable (workerd)

Note that before unjs/unenv#363 (2w ago), the Readable implementation was coming from unenv. It might explain why this code used to work.

Still I think { body: Readable.toWeb(ic) } should work and we should understand why it doesn't.

Other info:

I have tried to call Readable.isDisturbed(ic) right before the super constructor call and it returns false.

@jasnell could you please help investigate?