Undici throws a ConnectTimeoutError when there is no connection

Bug Description

If you try to send an HTTP request, but the DNS lookup for the requested domain name fails, Undici may throw a ConnectTimeoutError.

Reproducible By

I wrote a simple script which reproduces the issue

const { Pool } = require('undici')

const agent = new Pool('http://foobar.bar')

for (let i = 0; i < 500; i++) {
  agent.request({ method: 'GET', path: '/foobar' })
    .then(async ({ body }) => {
      for await (const data of body) {
        console.log('data', data.toString('utf8'))
      }
    })
    .catch(console.error)
}

I used undici@5.4.0

Expected Behavior

I’d expect to get only errors which indicate that the DNS lookup has failed.

Logs & Screenshots

Video

Environment

Ubuntu 20.04.4 LTS, Node v16.13.0

[jodevsa]

created the following PR: https://github.com/nodejs/undici/pull/1551

[jodevsa]

reproduce script:

const { Pool } = require('undici')
const assert = require('assert')
const agent = new Pool('http://foobar.bar')

for (let i = 0; i < 50000; i++) {
  agent.request({ method: 'GET', path: '/foobar' })
    .then(async ({ body }) => {
      for await (const data of body) {
        console.log('data', data.toString('utf8'))
      }
    })
    .catch((e)=>assert.equal(e.code,'ENOTFOUND'))
}