Merge the results of `arp -a` with known device information for improved output

arp.js

#!/usr/bin/env node
// @ts-check
const fs = require("fs");
const { spawn } = require("child_process");

const ipAddressRegExp = /\((?<ipAddress>\d{1,3}\.\d{1,3}\.\d{1,3}\.\d{1,3})\)/;
const macAddressRegExp = /(?<macAddress>[a-fA-F\d]{1,2}:[a-fA-F\d]{1,2}:[a-fA-F\d]{1,2}:[a-fA-F\d]{1,2}:[a-fA-F\d]{1,2}:[a-fA-F\d]{1,2})/;

function normalizeMACAddress(macAddress) {
  return macAddress
    .split(":")
    .reduce((macAddress, p) => {
      const pair = p.length === 2 ? p : `0${p}`;
      return macAddress.concat(pair.toUpperCase());
    }, [])
    .join(":");
}

function deviceFromCSV(str) {
  const arr = str.trim().split(",");
  return {
    device: arr[0],
    location: arr[1],
    connection: arr[2].toLowerCase(),
    macAddress: normalizeMACAddress(arr[3]),
    ipAddress: arr[4]
  };
}

const knownDevices = fs
  .readFileSync("./internet.csv", "utf8")
  .split("\n")
  .map(deviceFromCSV);

function deviceFromARP(str) {
  const arr = str.trim().split(" ");
  const macAddress = macAddressRegExp.exec(arr[3]);
  const ipAddress = ipAddressRegExp.exec(arr[1]);
  return {
    ...(arr[0] !== "?" ? { hostname: arr[0] } : {}),
    macAddress:
      macAddress && macAddress.groups
        ? normalizeMACAddress(macAddress.groups.macAddress)
        : null,
    ipAddress: ipAddress && ipAddress.groups ? ipAddress.groups.ipAddress : null
  };
}

const arp = spawn("arp", ["-a"]);
arp.stdout.on("data", data => {
  const arpDevices = data
    .toString()
    .split("\n")
    .map(deviceFromARP)
    .filter(({ ipAddress, macAddress }) => ipAddress && macAddress)
    .filter(
      ({ ipAddress, macAddress }) =>
        ipAddress.startsWith("192.168") && macAddress !== "FF:FF:FF:FF:FF:FF"
    );

  const mergedDevices = arpDevices.map(arpDevice => {
    const knownDevice = knownDevices.find(
      ({ macAddress }) => macAddress === arpDevice.macAddress
    );
    return {
      ...knownDevice,
      ...arpDevice
    };
  });

  console.log(mergedDevices);
});
arp.stderr.on("data", data => console.error(data.toString()));
arp.on("close", code => code !== 0 && process.exit(code));

internet.csv