Bun extra stdio fd's + IPC

child.js

import fs from 'node:fs'
import { log } from './log.js'

const fds = fs.readdirSync('/dev/fd').join(' ')
console.log('child.fds', fds)

process.send('test IPC')
log('node', 3)

log.js

import fs from 'node:fs'

export function log(proc, fd) {
  const reader = fs.createReadStream(null, { fd })
  const td = new TextDecoder()

  const writer = fs.createWriteStream(null, { fd })

  async function read() {
    for await (const chunk of reader) {
      const text = td.decode(chunk)
      console.log(`[${proc}]:${fd} >read :: ${text}`)
    }
  }

  function write() {
    writer.write(`[${proc}]:${fd} >write`)
  }

  read()
  write()

  setInterval(write, 2_000)
}

parent-bun.js

import Bun from 'bun'
import { log } from './log.js'

const child = Bun.spawn({
  cmd: ['node', 'child.js'],
  stdio: ['inherit', 'inherit', 'inherit', 'pipe'],
  serialization: 'json',
  ipc(msg) {
    console.log('[bun] IPC', msg)
  },
  onExit(_, exitCode) {
    console.log('[bun] child.exitCode', exitCode)
  }
});

console.log('child.stdio', child.stdio)
log('bun', child.stdio.at(-1))