eventStream.push hangs when called before eventStream.send()

[rrd108]

Environment

node v20.13.0
h3: 1.13.0

Reproduction

https://github.com/rrd108/h3-eventstream-push-hang

Steps to reproduce:

• clone
• pnpm i
• pnpm start
• open http://localhost:3000/stream

Describe the bug

The eventStream.push method in h3 hangs indefinitely when called before the eventStream.send() method is invoked.

This prevents the server from sending the stream to the client and causes a stall. The issue occurs even with a single call to eventStream.push before send and it is not related to backpressure.
The WritableStream reports it's ready before the push, and the problem is present even if we await the ready promise before the write operation.

Additional context

No response

Logs

No response

[Maxttier]

#940

[rrd108]

Thanks

[Maxttier]

@rrd108 do something?

[rrd108]

I solved it using the package you reccomended here #940 (comment)

[kricsleo]

Here's an example for Server-Sent Events (SSE): https://h3.dev/guide/websocket#example

In short, avoid blocking eventStream.send() with eventStream.push.

In your example, you can simply do the following:

    (async () => {
        console.log('before eventStream.push()')
        for (const message of messages) {
            console.log('before eventStream.push()')
            await eventStream.push(message)
            console.log('after eventStream.push()')
        }
        console.log('👉 NOW YOU GET HERE')
        await eventStream.close()
    })()
    
    // Do not block this
    return eventStream.send()