bug-core.mjs

import { createServer } from 'http'
import { connect } from 'net'

const server = createServer(function (req, res) {
  console.log('request!')
  server.close()
  res.setHeader('Connection', 'close')
  res.end('hello world')
})

await new Promise((resolve) => { server.listen(3000, resolve) })

const client = connect({ port: 3000 })

function sendRequest() {
  client.cork()
  client.write('GET / HTTP/1.1\r\n')
  client.write('Host: localhost:3000\r\n')
  client.write('User-Agent: curl/7.79.1\r\n')
  client.write('Accept: */*\r\n')
  client.write('\r\n')
  client.uncork()
}

sendRequest()
sendRequest()
sendRequest()

client.pipe(process.stdout)
// There should be 3 requests not two

bug.mjs

import { createServer } from 'http'
import { connect } from 'net'
import { Client } from 'undici'

const server = createServer(function (req, res) {
  console.log('request!')
  server.close()
  res.setHeader('Connection', 'close')
  res.end('hello world')
})

await new Promise((resolve) => { server.listen(3000, resolve) })

const client = new Client('http://localhost:3000', {
  pipelining: 1
})

const responses = await Promise.all([
  client.request({
    path: '/',
    method: 'GET' 
  }),

  client.request({
    path: '/',
    method: 'GET' 
  }),

  client.request({
    path: '/',
    method: 'GET' 
  })
])

const statusCodes = responses.map(r => r.statusCode)
console.log(statusCodes)

await client.close()

console.log('all good')