next.js/packages/next/src/lib/get-network-host.ts

import os from 'os'

function getNetworkHosts(family: 'IPv4' | 'IPv6'): string[] {
  const interfaces = os.networkInterfaces()
  const hosts: string[] = []

  Object.keys(interfaces).forEach((key) => {
    interfaces[key]
      ?.filter((networkInterface) => {
        switch (networkInterface.family) {
          case 'IPv6':
            return (
              family === 'IPv6' &&
              networkInterface.scopeid === 0 &&
              networkInterface.address !== '::1'
            )
          case 'IPv4':
            return family === 'IPv4' && networkInterface.address !== '127.0.0.1'
          default:
            return false
        }
      })
      .forEach((networkInterface) => {
        if (networkInterface.address) {
          hosts.push(networkInterface.address)
        }
      })
  })

  return hosts
}

export function getNetworkHost(family: 'IPv4' | 'IPv6'): string | null {
  const hosts = getNetworkHosts(family)
  return hosts[0] ?? null
}