What has changed in response.body.cancel() between node 20 and 21?

[elf-pavlik]

I have an integration test for a server streaming HTTP responses.

This integration test worked fine on node 20 but failed on node 21 and 22.
The failure was related to the server.close() not resolving due to the open connections. I'm relying on

const reader = response.body.getReader()
try {
  /* read some chunks */
}
finally {
  reader.releaseLock()
  await response.body.cancel()
}

At the end of the tests, server.close() resolves just fine on node 20.

With node 21 and 22 I had to call server.closeAllConnections() first for the server.close() to resolve.

In the end I changed all the tests to use

const response = await fetch(iri, {
  dispatcher: new Agent({ bodyTimeout: 1000 }),
});

This also ensures that all the connections close and that server.close() resolves on nodes 21 and 22.

While this might be enough for my tests, I still would like to understand why the connections appear to stay open after response.body.cancel() resolves.

[mcollina]

Could you prepare a complete example to reproduce? I have a feeling on why but I would need to investigate.

[elf-pavlik]

First, an extra clarification: The client works as expected on node 20 and 22.1, while it seems to leave the connection open on node 21 and 22.0. The node version that the server is run with doesn't seem to matter.

The difference is when the scripts exit and when they don't.

server.mjs

import { createServer } from 'node:http'

// create server
const server = createServer()

server.listen(5000)

server.on('request', async(req, res) => {
  res.write('hello')
  server.close()
  // if added both scripts will also exit on 21 and 22.0
  //server.closeAllConnections()
})

client.mjs

// import { Agent } from "undici"
const url = 'http://localhost:5000'

const response = await fetch(url, {
  // if added both scripts will also exit on 21 and 22.0
  // dispatcher: new Agent({ bodyTimeout: 1000 })
})

const reader = response.body.getReader();

try {
  await reader.read()
} finally {
  reader.releaseLock();
  await response.body.cancel();
}

I left comments that can force the disconnect from either the server or client that also work on node 21 and 22.0

[mcollina]

I have a feeling we added a bug somewhat earlier that it was then fixed. I've added a test for this exact case, so we know we won't regress anymore: #3219.

You can expect the version of undici in 22.1.0 to reach 20 in the next quarter.