[v2] SSE connection close leads to [ERR_STREAM_PREMATURE_CLOSE]: Premature close

[dan-lee]

I've got a simple worker with handling SSE:

// worker.js
export default {
  async fetch() {
    const { readable, writable } = new TransformStream()
    const encoder = new TextEncoder()
    const writer = writable.getWriter()

    setInterval(() => {
      writer.write(encoder.encode(`data: hello\n\n`))
    }, 2000)

    return new Response(readable, {
      status: 200,
      headers: {
        'Content-Type': 'text/event-stream',
        'Cache-Control': 'no-cache',
        Connection: 'keep-alive',
      },
    })
  },
}

and the runner (node --experimental-vm-modules run.js)

// run.js
import { Miniflare } from 'miniflare'

new Miniflare({
  scriptPath: './worker.js',
  modules: true,
}).startServer()

Now opening up http://localhost:8787 waiting for a few events and closing the page leads to miniflare crashing with the following node error:

node:internal/process/promises:246
          triggerUncaughtException(err, true /* fromPromise */);
          ^

Error [ERR_STREAM_PREMATURE_CLOSE]: Premature close
    at new NodeError (node:internal/errors:371:5)
    at ServerResponse.onclose (node:internal/streams/end-of-stream:140:30)
    at ServerResponse.emit (node:events:402:35)
    at Socket.onServerResponseClose (node:_http_server:235:23)
    at Socket.emit (node:events:402:35)
    at TCP.<anonymous> (node:net:687:12) {
  code: 'ERR_STREAM_PREMATURE_CLOSE'

This problem does not occur with v1.4.1

[mrbbot]

Hey! 👋 miniflare@2.0.0-rc.3 has just been released, including the fix for this. You can find the changelog here.